# Past Events

Bay Area Cold Atom Meeting (BACAM)

Wednesday, August 12, 2015

10:30 am - 6:00 pm

Location: Berkeley, CA, United States

Abstract
Kristi Beck (MIT)

Continuous Nondestructive Detection of Optical Photons

Continuous Nondestructive Detection of Optical Photons

Monday, August 24, 2015

1:30 pm - 2:30 pm

Location: PAB 214

AbstractThe nondestructive detection of optical photons is an enabling technology with applications in quantum information, simulation and communication. We present a detection scheme that continuously detects photons without destroying them. Photons to be measured are sent through an ensemble of Cesium atoms, where they travel as slow-light polaritons that are, in turn, coupled to a high finesse optical cavity. The atomic component of the polariton rotates the polarization of light that is transmitted through the cavity, which we detect. We show that the system is capable of non-destructively detecting individual signal photons by measuring a second-order correlation function between the signal and detection paths of g_2(0)>5.

Andy Geraci (U. of Nevada, Reno)

Sensitive force measurements with optically levitated microspheres

Sensitive force measurements with optically levitated microspheres

Monday, October 12, 2015

4:00 pm - 5:30 pm

Location: Spilker 232

AbstractLight carries momentum and can exert substantial forces on micro- and macroscopic objects ranging from single atoms to kg-scale mirrors. In high vacuum, optically levitated dielectric microspheres achieve excellent decoupling from their environment and experience minimal friction. Hence they can be used for sensitive force measurements. We have shown that such beads can be stably trapped under high vacuum conditions for long time periods and can be used for attonewton force measurements in a dual beam optical trap. I will describe our progress towards using these sensors for tests of the Newtonian gravitational inverse square law at micron length scales. Optically levitated dielectric objects also show promise for a variety of other applications, including searches for gravitational waves and experiments involving quantum optomechanics.

[1] G. Ranjit, D. Atherton, J. Stutz, M. Cunningham, and A.A. Geraci, Phys. Rev. A 91, 051805(R) (2015).

[2] A. Arvanitaki and A. A. Geraci, Phys. Rev. Lett. 110, 071105 (2013).

[3] A.A.Geraci, S.B.Papp, and J.Kitching, Phys. Rev. Lett. 105, 101101 (2010).

[1] G. Ranjit, D. Atherton, J. Stutz, M. Cunningham, and A.A. Geraci, Phys. Rev. A 91, 051805(R) (2015).

[2] A. Arvanitaki and A. A. Geraci, Phys. Rev. Lett. 110, 071105 (2013).

[3] A.A.Geraci, S.B.Papp, and J.Kitching, Phys. Rev. Lett. 105, 101101 (2010).

Hakan Tureci (Princeton)

Cavity QED Lattices: A platform to study many-body physics with photons

Cavity QED Lattices: A platform to study many-body physics with photons

Monday, October 26, 2015

4:00 pm - 5:30 pm

Location: Spilker 232

AbstractQuantum matter coupled to enhanced optical fields in confined geometries such as resonators and waveguides offer a promising platform to study emergent phenomena far-from-equilibrium [1]. In my talk I will discuss our recent efforts [2,3,4] at understanding what a quantum phase transition of photons may look like in a lattice of Cavity Quantum Electrodynamics systems, where photons become itinerant. Surprisingly this has lead us back to the very origin of Quantum Electrodynamics and the Quantum Theory, namely to Planck and Einstein's theory of thermal cavity radiation. We find a modification to the Planck-Einstein theory due to the backaction from (material) oscillators and show that a Cavity QED network displays an instability towards a ferroelectric phase when light-matter coupling is sufficiently increased. The true potential of coupled light-matter systems is however unleashed in driven Cavity QED networks [4]. I will discuss a general method to use photon-mediated interactions between qubits to drive them to a long-distance entangled state with an arbitrarily long lifetime [5]. We find that photon-mediated interactions provide a highly versatile toolbox to engineer the unitary and dissipative dynamics of spatially separated qubits, with important implications for dissipative stabilization of pure many-body states of qubits [6].

[1] A. Houck, H. E. Tureci, J. Koch, Nature Physics 8, 292 (2012).

[2] M. Schiro, M. Bordyuh, B. Oztop, H. E. Tureci, Phys. Rev. Lett. 109, 053601 (2012).

[3] M. Schiro, M. Bordyuh, B. Oztop, H. E. Tureci, J. Phys. B 46, 224021 (2013).

[4] M. Schiro et al, arxiv:1503.04456

[5] C. Aron, M. Kulkarni, H. E. Tureci, Phys. Rev. A 90, 062305 (2014).

[6] C. Aron, M. Kulkarni, H. E. Tureci, arxiv:1412.8477

[1] A. Houck, H. E. Tureci, J. Koch, Nature Physics 8, 292 (2012).

[2] M. Schiro, M. Bordyuh, B. Oztop, H. E. Tureci, Phys. Rev. Lett. 109, 053601 (2012).

[3] M. Schiro, M. Bordyuh, B. Oztop, H. E. Tureci, J. Phys. B 46, 224021 (2013).

[4] M. Schiro et al, arxiv:1503.04456

[5] C. Aron, M. Kulkarni, H. E. Tureci, Phys. Rev. A 90, 062305 (2014).

[6] C. Aron, M. Kulkarni, H. E. Tureci, arxiv:1412.8477

Eleftherios Goulielmakis (MPQ)

Attosecond Electronics: Tracing and Controlling Electrons in Real Time

Attosecond Electronics: Tracing and Controlling Electrons in Real Time

Monday, November 2, 2015

4:00 pm - 5:30 pm

Location: Spilker 232

AbstractHaving the shortest optical1,2,3 and soft x-ray fields4 as a part of its repertoire, attosecond physics has recently opened up new avenues for exploring ultrafast electronic processes in atoms5,6, molecules7, surfaces8 and nanostructures9. I will discuss how modern advancements of the “ultrafast toolbox” allow for the first time, the exploration and control of fundamental electronic phenomena in condensed media. Electron motion in bulk media, driven by intense, precisely-sculpted, optical fields give rise to controllable electric currents, the frequency of which extends to the multi-Petahertz range9-10, advancing lightwave electronics10 to new realms of speed and precision. Coherent extreme ultraviolet radiation emerging by these coherent charge oscillations9 offers direct insight into structural and dynamical properties of the underlying medium which were previously inaccessible to conventional solid-state spectroscopies. By endowing essential x-ray spectroscopies of solids with attosecond temporal resolution, optical half-cycle fields, combined with extreme ultraviolet pulses, offer for the first time, access into the attosecond dephasing of electronic excitation of highly-correlated condensed phase electronic systems11. We anticipate these new capabilities to result in far reaching implications to fundamental and applied, electronic and photonic sciences.

[1] Goulielmakis E. et al., Science 305, 1267 (2004) [2] Wirth A. et al., Science 334, 195 (2011). [3] Hassan M. Th et al., Nature submitted ( 2015) [4] Goulielmakis E.et al., Science 320, 1614 (2008).[5] Goulielmakis E. et al., Nature 466, 739 (2010). [6] Kienberger R. et al., Nature 427, 817 (2004) [6], Smirnova et. al, Nature 460,972(2009) [7] Cavalieri A L et al., Nature 449,1029 (2007) [8] Krueger M et al. Nature 475,78 (2011) [9] Luu T.T. et al., Nature 521,498 (2015), Garg el., Submitted (2015), [10] Goulielmakis E. et al., Science 317, 769 (2007). [11] Moulet A. et al., in preparation (2015)

[1] Goulielmakis E. et al., Science 305, 1267 (2004) [2] Wirth A. et al., Science 334, 195 (2011). [3] Hassan M. Th et al., Nature submitted ( 2015) [4] Goulielmakis E.et al., Science 320, 1614 (2008).[5] Goulielmakis E. et al., Nature 466, 739 (2010). [6] Kienberger R. et al., Nature 427, 817 (2004) [6], Smirnova et. al, Nature 460,972(2009) [7] Cavalieri A L et al., Nature 449,1029 (2007) [8] Krueger M et al. Nature 475,78 (2011) [9] Luu T.T. et al., Nature 521,498 (2015), Garg el., Submitted (2015), [10] Goulielmakis E. et al., Science 317, 769 (2007). [11] Moulet A. et al., in preparation (2015)

Ania Jayich (UCSB)

Quantum sensing and imaging with diamond spins

Quantum sensing and imaging with diamond spins

Monday, November 9, 2015

4:00 pm - 5:30 pm

Location: Spilker 232

Laura De Lorenzo

Exploring the Macroscopic Quantum Physics of Motion with Superfluid He-4

Exploring the Macroscopic Quantum Physics of Motion with Superfluid He-4

Tuesday, November 10, 2015

3:30 pm - 4:30 pm

Location: Spilker 317

Aash Clerk (McGill)

New approaches for realizing topological and non-reciprocal photonic states

New approaches for realizing topological and non-reciprocal photonic states

Monday, November 16, 2015

4:00 pm - 5:30 pm

Location: Spilker 232

Darrick Chang (ICFO)

Engineering quantum atom-light interactions with photonic crystals

Engineering quantum atom-light interactions with photonic crystals

Monday, November 30, 2015

4:00 pm - 5:30 pm

Location: Spilker 232

AbstractSignificant efforts have been made to interface cold atoms with micro- and nano-photonic systems in recent years. Originally, it was envisioned that the migration to these systems from free-space atomic ensemble or macroscopic cavity QED experiments could dramatically improve figures of merit and facilitate scalability in applications such as quantum information processing. However, there is a growing body of work pointing to an even more intriguing possibility, that nanophotonic systems can yield fundamentally new paradigms to manipulate quantum light-matter interactions, which do not have an obvious counterpart in macroscopic setups. Here, we describe an example of such a new possibility, involving the coupling of atoms to photonic crystals. In particular, we show that when atoms have transition frequencies aligned within photonic crystal bandgaps, the atoms can become dressed by localized photonic "clouds" of tunable size. This cloud behaves much like an external cavity, but one which follows the position of the atom. This phenomenon allows one to mediate and control long-range interactions between atomic internal degrees of freedom (spin), atomic motion (phonons), and photons. The multi-physics coupling can be utilized to design quantum systems with a rich variety of functionalities. We will discuss several examples, including strongly correlated many-body states of atomic spin and motion, and the "binding" of photons into extended molecules.

BIOGRAPHY

Darrick Chang has been a professor at the Institute of Photonic Sciences (ICFO) in Barcelona since 2011, and leads the research group for Theoretical Quantum Nanophotonics. Previously, he received his B.S. and PhD degrees in physics from Stanford and Harvard, respectively, and was a postdoctoral fellow at the Institute for Quantum Information at Caltech. His group is broadly interested in the use of nanophotonic and nanomechanical systems as platforms for novel quantum devices and to explore new quantum phenomena. Specific research interests in recent years include the optical properties of graphene, interfaces between cold atoms and nanophotonic systems, optical trapping techniques, and quantum vacuum forces. He is the recipient of an ERC Starting Grant.

BIOGRAPHY

Darrick Chang has been a professor at the Institute of Photonic Sciences (ICFO) in Barcelona since 2011, and leads the research group for Theoretical Quantum Nanophotonics. Previously, he received his B.S. and PhD degrees in physics from Stanford and Harvard, respectively, and was a postdoctoral fellow at the Institute for Quantum Information at Caltech. His group is broadly interested in the use of nanophotonic and nanomechanical systems as platforms for novel quantum devices and to explore new quantum phenomena. Specific research interests in recent years include the optical properties of graphene, interfaces between cold atoms and nanophotonic systems, optical trapping techniques, and quantum vacuum forces. He is the recipient of an ERC Starting Grant.

James Thompson (JILA)

Breaking Quantum and Thermal Limits on Precision Measurements

Breaking Quantum and Thermal Limits on Precision Measurements

Monday, December 7, 2015

4:00 pm - 5:30 pm

Location: Spiker 232

AbstractOur lab has been asking the question: is it possible to exploit atom-atom correlations and entanglement to advance the field of precision measurement? We have explored this question along two fronts that surpass quantum and thermal limits on precision measurements: spin-squeezed states that surpass the standard quantum limit on phase estimation by as much as 17.6(4) dB, and superradiant lasers that could be 10,000 times less sensitive to thermal and technical vibrations of the optical cavity’s mirrors. These techniques may one day impact a broad range of quantum sensors and physical measurements including atomic clocks, matter-wave interferometers, and lasers with sub-millihertz linewidth or equivalent coherence lengths extending from the earth to the sun.

Mohammad Hafezi (U of Maryland)

Topological robustness in photonic systems

Topological robustness in photonic systems

Monday, December 14, 2015

4:15 pm - 5:45 pm

Location: Spiker 232

AbstractPhenomena associated with the topological properties of physical systems can be naturally robust against perturbations. The best known examples are quantum Hall effects in electronic system, where insensitivity to localproperties manifests itself as conductance through edge states that is insensitive to defects and disorder. In this talk, I demonstrate how similar physics can be observed for photons; specifically, how various quantum Hall Hamiltonians can be simulated in an optical platform. I report on the first observation of topological photonic edge states using silicon-on-insulator technology, and the measurement of the corresponding topological invariants. Furthermore, the addition of optical nonlinearity to this system provides a platform to implement fractional quantum Hall states of photons and anyonic states that have not yet been observed in any physical system. More generally, the application of these ideas could lead to the development of optical devices with built-in protection for classical and quantum information processing.

Biography

Mohammad Hafezi is an Assistant Professor of Electrical and Computer Engineering at the University of Maryland (UMD), and a fellow at the Joint Quantum Institute (NIST-UMD) and IREAP. After obtaining his Ph.D. from the Physics Department at Harvard University, he moved to the Joint Quantum Institute as a postdoc in 2009. His research is at the interface of theoretical and experimental quantum optics and condensed-matter physics with a focus on fundamental physics and applications in quantum information science, precision measurement, and integrated photonics. His recent awards include a Sloan Research Fellowship and a Young Investor award of the Office of Naval Research.

Biography

Mohammad Hafezi is an Assistant Professor of Electrical and Computer Engineering at the University of Maryland (UMD), and a fellow at the Joint Quantum Institute (NIST-UMD) and IREAP. After obtaining his Ph.D. from the Physics Department at Harvard University, he moved to the Joint Quantum Institute as a postdoc in 2009. His research is at the interface of theoretical and experimental quantum optics and condensed-matter physics with a focus on fundamental physics and applications in quantum information science, precision measurement, and integrated photonics. His recent awards include a Sloan Research Fellowship and a Young Investor award of the Office of Naval Research.

Alicia Kollar (Stanford)

Lucas Zipp (Stanford)

Lucas Zipp (Stanford)

Monday, January 4, 2016

4:00 pm - 5:30 pm

Location: Spilker 232

AbstractStanford Research Highlights:

Supermode-polariton condensation in a multimode cavity QED-BEC system (Alicia Kollar)

Investigations of many-body physics in an AMO context often employ a static optical lattice to create a periodic potential. Such systems, while capable of exploring, e.g., the Hubbard model, lack the fully emergent crystalline order found in solid state systems whose stiffness is not imposed externally, but arises dynamically. Our multimode cavity QED experiment is introducing a new method of generating fully emergent and compliant optical lattices to the ultracold atom toolbox and provides new avenues to explore quantum liquid crystalline order. Looking forward, spin glasses may arise due to the oscillatory, frustrated, and tunable-range interactions mediated by the photons in the multimode optical cavity. It will thus be possible to use spinful atoms in cavities to realize models of frustrated and/or disordered spin systems, including neuromorphic computation in the context of the Hopfield associative memory. We will present our first experimental result, the observation of a supermode-polariton condensate via a supermode superradiant phase transition.

Probing Ultrafast Electron Dynamics in Atoms and Molecules (Lucas Zipp)

As our ability to probe atomic and molecular processes in the time domain approaches the attosecond time scale, it has become possible (and necessary) to revisit some fundamental ideas on how processes like photoionization occur in the time domain. Several recent experiments have investigated measuring attosecond-scale “Wigner” delays in single photon ionization [1,2]. I will present our results extending these measurements to the strong field regime, allowing us to probe the intrinsic time delay experienced by an electron as it is ionized in a strong, nonperturbative laser field [3]. In the second part of the talk I will discuss a recent experiment tracking the angular motion of an electron wave packet in a Rydberg manifold of molecular nitrogen. We are able to see directly in the time domain a process of “l-uncoupling” that up until now has only been inferred from spectroscopic data [4].

[1] K. Klünder et al, "Probing Single-Photon Ionization on the Attosecond Time Scale," Phys. Rev. Lett. 106, 143002 (2011).

[2] M. Schultze et. al, "Delay in Photoemission," Science 328, 1658–1662 (2010).

[3] L. J. Zipp, A. Natan, and P. H. Bucksbaum, "Probing electron delays in above-threshold ionization," Optica 1, 361–364 (2014).

[4] R.-Y. Chang et al, "Observation of L uncoupling in the 5Δg1 Rydberg state of Na2," The Journal of Chemical Physics 123, 224303 (2005).

Supermode-polariton condensation in a multimode cavity QED-BEC system (Alicia Kollar)

Investigations of many-body physics in an AMO context often employ a static optical lattice to create a periodic potential. Such systems, while capable of exploring, e.g., the Hubbard model, lack the fully emergent crystalline order found in solid state systems whose stiffness is not imposed externally, but arises dynamically. Our multimode cavity QED experiment is introducing a new method of generating fully emergent and compliant optical lattices to the ultracold atom toolbox and provides new avenues to explore quantum liquid crystalline order. Looking forward, spin glasses may arise due to the oscillatory, frustrated, and tunable-range interactions mediated by the photons in the multimode optical cavity. It will thus be possible to use spinful atoms in cavities to realize models of frustrated and/or disordered spin systems, including neuromorphic computation in the context of the Hopfield associative memory. We will present our first experimental result, the observation of a supermode-polariton condensate via a supermode superradiant phase transition.

Probing Ultrafast Electron Dynamics in Atoms and Molecules (Lucas Zipp)

As our ability to probe atomic and molecular processes in the time domain approaches the attosecond time scale, it has become possible (and necessary) to revisit some fundamental ideas on how processes like photoionization occur in the time domain. Several recent experiments have investigated measuring attosecond-scale “Wigner” delays in single photon ionization [1,2]. I will present our results extending these measurements to the strong field regime, allowing us to probe the intrinsic time delay experienced by an electron as it is ionized in a strong, nonperturbative laser field [3]. In the second part of the talk I will discuss a recent experiment tracking the angular motion of an electron wave packet in a Rydberg manifold of molecular nitrogen. We are able to see directly in the time domain a process of “l-uncoupling” that up until now has only been inferred from spectroscopic data [4].

[1] K. Klünder et al, "Probing Single-Photon Ionization on the Attosecond Time Scale," Phys. Rev. Lett. 106, 143002 (2011).

[2] M. Schultze et. al, "Delay in Photoemission," Science 328, 1658–1662 (2010).

[3] L. J. Zipp, A. Natan, and P. H. Bucksbaum, "Probing electron delays in above-threshold ionization," Optica 1, 361–364 (2014).

[4] R.-Y. Chang et al, "Observation of L uncoupling in the 5Δg1 Rydberg state of Na2," The Journal of Chemical Physics 123, 224303 (2005).

Andrew Daley (University of Strathclyde)

Engineering coherent and dissipative dynamics with ultracold atoms

Engineering coherent and dissipative dynamics with ultracold atoms

Thursday, January 14, 2016

1:15 pm - 2:30 pm

Location: Spilker 317

AbstractIn recent years, systems of ultracold atoms in optical lattices have opened new opportunities for exploring time-dependent many-body dynamics. In addition to coherent phenomena, it has become possible to engineer open quantum systems, drawing new connections between many-body physics and concepts from quantum optics. Dissipation arises naturally in the form of light scattering and particle losses in these systems, and can also be directly engineered, e.g., by adding additional species to the experiment which act as a reservoir. This opens opportunities for exploring novel phenomena, and also finding new ways of preparing important many-particle states. I will discuss some of our recent theoretical work in this direction, including how effective three-body interactions between atoms in optical lattices can be controlled by photon-assisted tunnelling or enhanced via dissipative processes. I will also discuss how engineered dissipation or particle losses can be combined with properties of fermionic statistics to drive a system into entangled spin states, which have potential applications in quantum metrology.

Eugene Demler (Harvard)

Nonequilibrium dynamics of fermions: from resonant Xray scattering to photo-induced superconductivity to ultracold atoms

Nonequilibrium dynamics of fermions: from resonant Xray scattering to photo-induced superconductivity to ultracold atoms

Thursday, January 14, 2016

3:15 pm - 4:30 pm

Location: McCullough 115

AbstractNew experimental techniques in condensed matter physics go beyond the paradigm of linear response measurements. I will use examples of resonant Xray scattering in high Tc cuprates and photo-induced superconductivity to demonstrate how new insights into experimental results can be gained by considering their nonequilibrium aspects. I will also discuss on-going experiments with ultracold atoms that can help address open problems of quantum dynamics of many-body fermionic systems.

Arghavan Safavi-Naini(JILA, NIST & CU Boulder)

Exploration of Many-body Dynamics with Polar Molecules

Exploration of Many-body Dynamics with Polar Molecules

Friday, January 15, 2016

2:30 pm - 4:00 pm

Location: PAB 232

AbstractUltracold polar molecules featuring long-range and anisotropic dipolar interactions are emerging as a unique platform for the quantum simulation of a variety of rich and important phenomena ranging from quantum magnetism, to many-body localization, to synthetic spin-orbit coupling. However to take fully advantage of those capabilities and investigate the plethora of exotic quantum phases hosted by them it is fundamental to reach low entropy conditions.

In this talk I will describe how the combined effects of interactions, temperature, and adiabatic loading in an optical lattice act as an obstacle to the experimental realization of a low-entropy gas of polar molecules through magnetoassociation of initially prepared quantum degenerate atomic gases. Careful considerations of these effects has been key for increasing the filling fraction in recent polar molecule experiments.

Moreover, I will describe a recent experiment conducted at JILA where a lattice gas of polar molecules has been used to create a clean and tunable distribution where sites are either empty or occupied by a doublon made of one boson and one fermion. I will discuss theoretical models based on analytical methods and numerical simulations, that capture the observed far from equilibrium, many-body dynamics of the bose-fermi mixture.

Biography

I am a research fellow at JILA, NIST and CU Boulder in the group of Ana Maria Rey. I work closely with the polar molecules experiment at JILA and the trapped-ion experiments at NIST. I develop analytic methods and numerical tools to analyze equilibrium and out-of-equilibrium properties of many-body quantum systems.

In this talk I will describe how the combined effects of interactions, temperature, and adiabatic loading in an optical lattice act as an obstacle to the experimental realization of a low-entropy gas of polar molecules through magnetoassociation of initially prepared quantum degenerate atomic gases. Careful considerations of these effects has been key for increasing the filling fraction in recent polar molecule experiments.

Moreover, I will describe a recent experiment conducted at JILA where a lattice gas of polar molecules has been used to create a clean and tunable distribution where sites are either empty or occupied by a doublon made of one boson and one fermion. I will discuss theoretical models based on analytical methods and numerical simulations, that capture the observed far from equilibrium, many-body dynamics of the bose-fermi mixture.

Biography

I am a research fellow at JILA, NIST and CU Boulder in the group of Ana Maria Rey. I work closely with the polar molecules experiment at JILA and the trapped-ion experiments at NIST. I develop analytic methods and numerical tools to analyze equilibrium and out-of-equilibrium properties of many-body quantum systems.

Irfan Siddiqi (UC Berkeley)

Unraveling the Quantum Ensemble

Unraveling the Quantum Ensemble

Monday, February 1, 2016

4:00 pm - 5:30 pm

Location: Spilker 232

AbstractIn the quantum world, an object can simultaneously exist in multiple states – the “dead” and “alive” realizations of Schrödinger’s proverbial feline being a quintessential example. It is the act of measurement which drives such an exotic superposition to a more familiar classical outcome, “dead” or “alive” for the cat, thus bridging the gap between quantum mechanics and our concept of reality. However, the precise nature of this so-called wavefunction collapse remains a topic of debate at the intersection of physics, mathematics, and philosophy. Applying continuous weak measurement techniques in conjunction with Bayesian statistics to superconducting quantum circuits, we reconstruct the real-time collapse of the wavefunction describing a two-state system at the level of the individual constituent quantum trajectories that form an ensemble measurement. With this dense dataset, a variety of statistical metrics can be extracted, including the most probable path—analogous to the geodesic in space-time—between two points in Hilbert space.

Bio: A professor of physics at the University of California, Berkeley, my work is primarily experimental and focuses on the development of superconducting quantum electronics, with an emphasis on quantum information processing and quantum control. In particular, we seek to answer fundamental questions in quantum theory as well as to engineer devices that harness quantum coherence. Recent explorations include quant

Bio: A professor of physics at the University of California, Berkeley, my work is primarily experimental and focuses on the development of superconducting quantum electronics, with an emphasis on quantum information processing and quantum control. In particular, we seek to answer fundamental questions in quantum theory as well as to engineer devices that harness quantum coherence. Recent explorations include quant

Eric Cornell (JILA / CU Boulder)

Physics Department Colloquium

Physics Department Colloquium

Tuesday, February 9, 2016

4:30 pm - 5:30 pm

Location: Hewlett 201

Tracy Li (Ludwig-Maximilians-Universität)

Probing Bloch band geometry in an optical honeycomb lattice

Probing Bloch band geometry in an optical honeycomb lattice

Wednesday, February 17, 2016

1:30 pm - 3:00 pm

Location: PAB232

AbstractIn recent decades, there has been intense interest in understanding the role of geometry in band structures. In contrast to solid state systems, where geometric effects are usually observed through the response of other quantities, ultracold atoms in optical lattices offer the unique possibility of directly probing the geometry of the band eigenstates. Using a BEC in a graphene-type hexagonal lattice, we directly probe band geometry by combining Ramsey interferometry with a gradient. First, using a weak gradient, we realize an atomic interferometer in reciprocal space to detect the singular π Berry flux localized at each Dirac point, in analogy to an Aharonov-Bohm interferometer that measures the magnetic flux through an area in real-space . Next, using a strong gradient, we realize dynamics that are described by Wilson lines, which are generalizations of Berry phases to multiple, degenerate bands. We demonstrate that probing the evolution in band populations enables a tomographic reconstruction of the cell-periodic Bloch functions at any quasimomentum.

Biography

Tracy is currently a PhD student in the group of Immanuel Bloch in Munich. Previously, she received her B.Sc in physics at MIT.

Biography

Tracy is currently a PhD student in the group of Immanuel Bloch in Munich. Previously, she received her B.Sc in physics at MIT.

Sebastian Hild (Max-Planck-Institut für Quantenoptik)

Entanglement dynamics in a one dimensional optical lattice and many body localization of a two dimensional bosonic gas

Entanglement dynamics in a one dimensional optical lattice and many body localization of a two dimensional bosonic gas

Monday, February 29, 2016

2:00 pm - 3:30 pm

Location: PAB214

AbstractTwo component ultra-cold bosonic gases in optical lattices are an excellent

quantum simulator. We will present two examples in this talk.

The first part focuses on the near perfect implementation of Heisenberg chains

which is achieved using a single component Mott insulating state. Single site

addressing techniques are applied to manipulate the local spin population.

Quantum as well as thermal fluctuations cause a residual hole probability in the

initial state and the impact on coherent spin transport is an open question. We

experimentally show that coherent spin transport under these conditions is

indeed possible. Propagation of a single spin impurity results in entanglement

spreading along the spin chain which we directly detect by measuring the

concurrence between pairs of lattice sites.

The second part of the talk will be about many-body localization (MBL). Under

which conditions well isolated quantum systems do thermalize is a fundamental

question. MBL marks a general class of systems which do not thermalize.

Microscopic detection of diverging observables near the phase transition remains

experimentally challenging, and demonstration of the MBL in higher dimensions

is still demanding. We report on recent experiments on MBL of Bosons in a two

dimensional square lattice. We prepare a structured highly excited Mott insulating

state which relaxes to a thermal state for vanishing disorder. A projected on-site

random disorder potential changes the time evolution significantly and leads to

non ergodic behavior. Employing single site and single atom sensitivity we use

local observables to quantify the dynamics of the bosonic many body state for

different disorder strength. We observed the phase transition to MBL to occur

only above a critical disorder strength for interacting Bosons.

Biography

Sebastian received his Bachelor degree in 2009 at the Rheinischen Friedrich Wilhelms-Universitat Bonn, Germany with a Bachelor project on "Laser Frequency Stabilization using heterodyne interferometry for the LISA Space-craft Mission“ at the University of Florida. Afterwards He worked on "Resolved Raman sideband cooling in a doughnut-shaped optical trap“ in the group of Prof. Dieter Meschede and obtained his Master degree in 2011 from the Rheinischen Friedrich Wilhelms-Universitat Bonn, Germany. Since 2012 he is a doctoral candidate at the Max--Planck-Institut für Quantenoptik in Garching, Germany within the group of Prof. Immanuel Bloch. He is working at the single atom experiment on simulation of spin models and many-body dynamics.

quantum simulator. We will present two examples in this talk.

The first part focuses on the near perfect implementation of Heisenberg chains

which is achieved using a single component Mott insulating state. Single site

addressing techniques are applied to manipulate the local spin population.

Quantum as well as thermal fluctuations cause a residual hole probability in the

initial state and the impact on coherent spin transport is an open question. We

experimentally show that coherent spin transport under these conditions is

indeed possible. Propagation of a single spin impurity results in entanglement

spreading along the spin chain which we directly detect by measuring the

concurrence between pairs of lattice sites.

The second part of the talk will be about many-body localization (MBL). Under

which conditions well isolated quantum systems do thermalize is a fundamental

question. MBL marks a general class of systems which do not thermalize.

Microscopic detection of diverging observables near the phase transition remains

experimentally challenging, and demonstration of the MBL in higher dimensions

is still demanding. We report on recent experiments on MBL of Bosons in a two

dimensional square lattice. We prepare a structured highly excited Mott insulating

state which relaxes to a thermal state for vanishing disorder. A projected on-site

random disorder potential changes the time evolution significantly and leads to

non ergodic behavior. Employing single site and single atom sensitivity we use

local observables to quantify the dynamics of the bosonic many body state for

different disorder strength. We observed the phase transition to MBL to occur

only above a critical disorder strength for interacting Bosons.

Biography

Sebastian received his Bachelor degree in 2009 at the Rheinischen Friedrich Wilhelms-Universitat Bonn, Germany with a Bachelor project on "Laser Frequency Stabilization using heterodyne interferometry for the LISA Space-craft Mission“ at the University of Florida. Afterwards He worked on "Resolved Raman sideband cooling in a doughnut-shaped optical trap“ in the group of Prof. Dieter Meschede and obtained his Master degree in 2011 from the Rheinischen Friedrich Wilhelms-Universitat Bonn, Germany. Since 2012 he is a doctoral candidate at the Max--Planck-Institut für Quantenoptik in Garching, Germany within the group of Prof. Immanuel Bloch. He is working at the single atom experiment on simulation of spin models and many-body dynamics.

Philipp Treutlein (U. of Basel)

Bell correlations in a Bose-Einstein condensate

Bell correlations in a Bose-Einstein condensate

Friday, March 11, 2016

2:30 pm - 5:30 pm

Location: PAB 232

AbstractThe parts of a composite system can share correlations that are stronger than any classical theory allows. These so-called Bell correlations can be confirmed by violating a Bell inequality and represent the most profound departure of quantum from classical physics. We report experiments where we detect Bell correlations between the spins of 480 atoms in a Bose-Einstein condensate [1]. We derive a Bell correlation witness from a recent many-particle Bell inequality [2] involving one- and two-body correlation functions only. Our measurement on a spin-squeezed state [3] exceeds the threshold for Bell correlations by 3.8 standard deviations. Concluding the presence of Bell correlations is unprecedented for an ensemble containing more than a few particles. Our work shows that the strongest possible non-classical correlations are experimentally accessible in many-body systems, and that they can be revealed by collective measurements. This opens new perspectives for using many-body systems in quantum information tasks.

[1] R. Schmied, J.-D. Bancal, B. Allard, M. Fadel, V. Scarani, P. Treutlein, N. Sangouard, to be published (2016).

[2] J. Tura, R. Augusiak, A.B. Sainz, T. Vértesi, M. Lewenstein, A. Acín, Science 344, 1256 (2014).

[3] M.F. Riedel, P. Böhi, Y. Li, T.W. Hänsch, A. Sinatra, P. Treutlein, Nature 464, 1170 (2010).

Short Biography

Philipp Treutlein, born in Reutlingen in 1976, studied physics at the Universities of Konstanz and Stanford in 1996-2002. At Stanford, he worked in the laboratory of Steven Chu on laser cooling and atom interferometry. Back in Konstanz, he joined Markus Oberthaler's group for his diploma thesis, investigating Bose-Einstein condensates in optical lattices. From 2002-2010, Philipp worked in the laboratory of Theodor W. Hänsch at LMU Munich and the Max-Planck-Institute of Quantum Optics, first as a doctoral student in Jakob Reichel's team and later as leader of his own group. During this time, he performed experiments with ultracold atoms in chip-based microtraps ("atom chips"). He demonstrated a chip-based atomic clock and an atom interferometer, carried out first experiments on quantum metrology with entangled atoms, and explored interfaces of atoms and mechanical oscillators. In 2010, Philipp was appointed as a tenure-track assistant professor at the University of Basel, where he set up a group working on ultracold atoms, optomechanics, and hybrid quantum systems. In February 2015 he was promoted to associate professor.

[1] R. Schmied, J.-D. Bancal, B. Allard, M. Fadel, V. Scarani, P. Treutlein, N. Sangouard, to be published (2016).

[2] J. Tura, R. Augusiak, A.B. Sainz, T. Vértesi, M. Lewenstein, A. Acín, Science 344, 1256 (2014).

[3] M.F. Riedel, P. Böhi, Y. Li, T.W. Hänsch, A. Sinatra, P. Treutlein, Nature 464, 1170 (2010).

Short Biography

Philipp Treutlein, born in Reutlingen in 1976, studied physics at the Universities of Konstanz and Stanford in 1996-2002. At Stanford, he worked in the laboratory of Steven Chu on laser cooling and atom interferometry. Back in Konstanz, he joined Markus Oberthaler's group for his diploma thesis, investigating Bose-Einstein condensates in optical lattices. From 2002-2010, Philipp worked in the laboratory of Theodor W. Hänsch at LMU Munich and the Max-Planck-Institute of Quantum Optics, first as a doctoral student in Jakob Reichel's team and later as leader of his own group. During this time, he performed experiments with ultracold atoms in chip-based microtraps ("atom chips"). He demonstrated a chip-based atomic clock and an atom interferometer, carried out first experiments on quantum metrology with entangled atoms, and explored interfaces of atoms and mechanical oscillators. In 2010, Philipp was appointed as a tenure-track assistant professor at the University of Basel, where he set up a group working on ultracold atoms, optomechanics, and hybrid quantum systems. In February 2015 he was promoted to associate professor.

Klemens Hammerer (Leibniz University of Hannover)

Entanglement of Matter and Continuous-Wave Light

Entanglement of Matter and Continuous-Wave Light

Monday, March 14, 2016

4:00 pm - 5:30 pm

Location: Spilker 232

AbstractThe generation of quantum states carrying entanglement among propagating light fields and stationary matter is a prerequisite for fundamental test of quantum mechanics, such as loophole free Bell tests, as well as for applications in quantum communication over long distances. Current experiments achieve a remarkably high efficiency in generating and controlling such entangled states of matter, such as single atoms, atomic ensembles, and even with micro-mechanical oscillators, with pulsed light. In my talk I will present our recent theoretical studies towards extending this to continuous-wave light which may provide new perspectives for experiments operating in the regime of strong cooperativity of light-matter interactions. In particular, I will show that this approach can be used to generate deterministically long-distance entanglement of material degrees of freedom, emulate many-body quantum dynamics, and perform analog variational calculations for models of quantum field theories.

Klemens Hammerer

Institute for Theoeretical Physics and Institute for Gravitational Physics (Albert-Einstein-Institute) Leibniz University of Hannover

Klemens Hammerer

Institute for Theoeretical Physics and Institute for Gravitational Physics (Albert-Einstein-Institute) Leibniz University of Hannover

Benjamin Lev (Stanford)

Physics Department Colloquium

Physics Department Colloquium

Tuesday, April 5, 2016

4:30 pm - 5:30 pm

Location: Hewlett 201

Theodor Hänsch (LMU Munich)

Hofstadter Lecture

Hofstadter Lecture

Tuesday, April 26, 2016

4:30 pm - 5:30 pm

Location: Hewlett 201

Mark Saffman (U. of Wisconsin)

Quantum computation with Rydberg atoms: across the periodic table and beyond

Quantum computation with Rydberg atoms: across the periodic table and beyond

Monday, May 2, 2016

4:00 pm - 5:30 pm

Location: Spilker 232

AbstractRecent years have witnessed substantial progress in using interactions between Rydberg excited atoms for quantum gates and entanglement generation. Nevertheless there remain several outstanding challenges that must be overcome to achieve scalable quantum computation. These include gate fidelity, atom loss, and quantum nondemolition state measurements without crosstalk to nearby qubits. After reviewing the current state of the art we will present some new ideas for simple solutions using complex atoms.

Jun Ye (JILA)

Physics Department Colloquium

Physics Department Colloquium

Tuesday, May 3, 2016

4:30 pm - 5:30 pm

Location: Hewlett 201

Arthur La Rooij (University of Amsterdam)

Towards Quantum Simulation with magnetic lattices

Towards Quantum Simulation with magnetic lattices

Wednesday, May 4, 2016

2:30 pm - 4:00 pm

AbstractWe use nano-lithography techniques to create lattice potentials in permanent magnetic films on atom chips. These lattices can be created over a large range of length scales and are used to trap mesoscopic clouds of ultracold atoms. In our current experiments we use a 10 micron lattice spacing to study Rydberg physics with clouds up to 400 atoms. In parallel, we are downscaling the lattice spacing for a new series of experiments. On these new atom chips we created lattices with lattice spacing varying from 250nm up to 5um on the same chip. I will discuss both the current experiments and the fabrication of these new magnetic potentials. These chips were patterned by e-beam lithography and etched with an Ar plasma to obtain structures with a 20nm resolution. This technique can extend the range of length scales of optical lattices to smaller scale's and therefore higher interaction energies, also it c an be used to study degenerate gases in completely engineered potential environments. In my talk I will focus on the fabrication of the magnetic chips, the construction of our new quantum gas experiment and I will show various new lattice geometries that we developed and simulated.

Holger Müller (UC Berkeley)

Hunting for dark energy in the lab

Hunting for dark energy in the lab

Monday, May 9, 2016

4:00 pm - 5:30 pm

Location: Spilker 232

AbstractDark energy could be a dynamic field - quintessence. The original and simplest model is based on so-called tracker potentials. Confirming this model would identify the dominant constituent of the universe and help understanding its history. In principle, this is possible by studying the history of the dark energy density, e.g., by improved supernova surveys, microwave-background-radiation or structure-formation studies.

Assuming a coupling between dark energy and normal matter, of roughly gravitational strength, allows us to detect search for quintessence by measuring its interaction with cold atoms in atom interferometers. We have already constrained the model more than 1000 times more strongly than the best previous experiment. Searching its entire parameter space is feasible and would either detect quintessence or rule out the model, thus characterizing the properties of dark energy.

Assuming a coupling between dark energy and normal matter, of roughly gravitational strength, allows us to detect search for quintessence by measuring its interaction with cold atoms in atom interferometers. We have already constrained the model more than 1000 times more strongly than the best previous experiment. Searching its entire parameter space is feasible and would either detect quintessence or rule out the model, thus characterizing the properties of dark energy.

Mikhail Lukin (Harvard)

Exploring New Frontiers of Quantum Optical Science

Exploring New Frontiers of Quantum Optical Science

Tuesday, May 17, 2016

4:30 pm - 5:30 pm

Location: Hewlett 201

AbstractWe will discuss recent developments at a new scientific interface between quantum optics, nanoscience and quantum information science. Specific examples include the use of quantum optical techniques for manipulation of individual atom-like impurities at a nanoscale and for realization of hybrid systems combining them with nanophotonic devices. We will discuss how these techniques are used for exploring quantum nonlinear optics and quantum networks, probing non-equilibrium quantum dynamics, and developing new applications such as magnetic resonance imaging with single atom resolution, and nanoscale sensing in biology and material science.

Rob Schoelkopf (Yale University)

Towards Quantum Computing With Superconducting Circuits: Extending the Lifetime of Information Through Quantum Error Correction

Towards Quantum Computing With Superconducting Circuits: Extending the Lifetime of Information Through Quantum Error Correction

Monday, May 23, 2016

3:00 pm - 4:30 pm

Location: Packard 101

AbstractDramatic progress has been made in the last decade and a half towards realizing solid-state systems for quantum information processing with superconducting quantum circuits. Artificial atoms (or qubits) based on Josephson junctions have improved their coherence times more than a million-fold, have been entangled, and used to perform simple quantum algorithms. The next challenge for the field is demonstrating quantum error correction that actually improves the lifetimes, a necessary step for building more complex systems. Here we demonstrate a fully operational quantum error correction system, based on a logical encoding comprised of superpositions of cat states in a superconducting cavity. This system uses real-time classical feedback to encode, track the naturally occurring errors, decode, and correct, all without the need for post-selection. Using this approach we reach, for the first time, the break-even point for QEC and preserve quantum information through active means. Moreover, the performance of the system matches with predictions, and can be dramatically improved by making the protocol more fault tolerant. Mastering the practice of error correction, and understanding the overhead and complexity required, are the main scientific challenges remaining for reaching scalable quantum computation with this technology.

Scott Parkins (University of Auckland)

Spin squeezing via engineered Dicke-model systems

Spin squeezing via engineered Dicke-model systems

Thursday, June 2, 2016

1:30 pm - 3:00 pm

Location: PAB 232

AbstractSpin-squeezed states have now been created in a range of atomic systems using a variety of methods. This talk looks at some promising alternative schemes for creating spin squeezing in cavity QED systems using cavity-mediated Raman transitions to engineer effective atom-photon and atom-atom interactions. These schemes follow on from the proposal of Dimer et al. [1] for the creation of a generalised, effective Dicke model of an ensemble of spin-1/2 atoms coupled to a cavity mode, including both linear and nonlinear (dispersive) atom-cavity couplings on a potentially equal footing [2]. We first examine this model in a regime where the dispersive coupling is very large and find that the steady state of the system can in fact be a strongly spin-squeezed Dicke state of the atomic ensemble. These states can offer Heisenberg-limited metrological properties and feature genuine multipartite entanglement amongst the entire atomic ensemble. We also consider a more general set of schemes, which utilise additional atomic internal (electronic) states or additional cavity modes to engineer alternative collective-spin models [3]. These models in turn lead to alternative methods for producing spin squeezed states not only of spin-1/2 systems, but also of integer-spin systems.

[1] F. Dimer, B. Estienne, A.S. Parkins and H.J. Carmichael, Proposed realization of the Dicke-model quantum phase transition in an optical cavity QED system, Phys. Rev. A. 75, 013804 (2007).

[2] A.L. Grimsmo and A.S. Parkins, Dissipative Dicke model with nonlinear atom-photon interaction, J. Phys. B: At. Mol. Opt. Phys. 46, 224012 (2013).

[3] S. Morrison and A.S. Parkins, Collective spin systems in dispersive optical cavity QED: quantum phase transitions and entanglement, Phys. Rev. A. 77, 043810 (2008).

[1] F. Dimer, B. Estienne, A.S. Parkins and H.J. Carmichael, Proposed realization of the Dicke-model quantum phase transition in an optical cavity QED system, Phys. Rev. A. 75, 013804 (2007).

[2] A.L. Grimsmo and A.S. Parkins, Dissipative Dicke model with nonlinear atom-photon interaction, J. Phys. B: At. Mol. Opt. Phys. 46, 224012 (2013).

[3] S. Morrison and A.S. Parkins, Collective spin systems in dispersive optical cavity QED: quantum phase transitions and entanglement, Phys. Rev. A. 77, 043810 (2008).

Cheng Chin (U. Chicago)

Scaling symmetry of topological defects in quantum critical dynamics

Scaling symmetry of topological defects in quantum critical dynamics

Monday, June 6, 2016

4:00 pm - 5:00 pm

Location: Spilker 232

AbstractSpanning condensed matter, cosmology, and quantum gases, evolution of many-body systems is hy-pothesized to be universal near a continuous phase transition. A long-sought signature of the universal dynamics is the scaling symmetry of emerging topological defects; examples include cosmic domains in early universe (T. Kibble, 1976), and vortices in quenched superfluid helium (W. Zurek, 1985).

We test the scaling symmetry and universality of quantum critical dynamics based on Bose-Einstein condensates of cesium atoms ramping across an effective ferromagnetic quantum phase transition. We observe a sudden growth of quantum fluctuations and domains separated by topological defects (domain walls). Intriguingly, the domains are anti-ferromagnetically ordered with record thermal energy scales as low as kB x 20pK. Time and length scales measured over a wide range of parameters yield precise temporal and spatial critical exponents of 0.50(2) and 0.26(2), respectively, consistent with theory. In the scaled space-time coordinate, correlations collapse to a single curve, in support of the universality hypothesis.

We test the scaling symmetry and universality of quantum critical dynamics based on Bose-Einstein condensates of cesium atoms ramping across an effective ferromagnetic quantum phase transition. We observe a sudden growth of quantum fluctuations and domains separated by topological defects (domain walls). Intriguingly, the domains are anti-ferromagnetically ordered with record thermal energy scales as low as kB x 20pK. Time and length scales measured over a wide range of parameters yield precise temporal and spatial critical exponents of 0.50(2) and 0.26(2), respectively, consistent with theory. In the scaled space-time coordinate, correlations collapse to a single curve, in support of the universality hypothesis.

Adam Kaufman (Harvard)

Quantum Thermalization through Entanglement

Quantum Thermalization through Entanglement

Thursday, June 30, 2016

1:00 pm - 2:00 pm

Location: Spilker 317

AbstractUnderstanding how an isolated many-body state thermalizes and develops entropy is foundational to quantum statistical mechanics, yet appears antithetical to basic notions that we have about entropy. An evolving quantum state can develop observables that agree with thermal ensembles, yet the unitarity of quantum evolution preserves the purity of this full quantum state in time. Hence, a pure, and in this sense, zero entropy quantum state can dynamically become seemingly entropic and thermal. In this talk, I will describe our experimental studies of thermalization in a verifiably pure many-body state, and how the entropy induced by entanglement facilitates thermalization. I will describe our experimental method for measuring quantum purity, and thereby entanglement entropy, through the interference of two copies of a many-body state. By comparing the entanglement entropy we measure to the thermal entropy expected from an ensemble, I will illustrate how thermalization is manifest locally within a globally pure quantum state, and how these observations are related to the Eigenstate Thermalization Hypothesis.

Bay Area Cold Atom Meeting (BACAM)

Wednesday, August 3, 2016

10:30 am - 6:30 pm

Location: Stanford University

Abstract
Pranjal Bordia (LMU Munich)

To Thermalize or Not to Thermalize: Probing Many-Body Localization with Ultracold Synthetic Matter

To Thermalize or Not to Thermalize: Probing Many-Body Localization with Ultracold Synthetic Matter

Wednesday, August 10, 2016

2:00 pm - 3:00 pm

AbstractA Many-Body Localized (MBL) system describes a generic phase of matter which, even with an infinite number of degrees of freedom, fails to thermalize. Surprisingly, this breakdown of thermalization can occur even in highly exited states. As such, this phase cannot be described by conventional quantum-statistical physics which assumes an underlying temperature of the many-body system. In this talk, I will describe how can one can use a highly controllable system of ultracold atoms in optical lattices to understand and probe such a quantum many-body system.

Disorder turns out to be the key ingredient in realizing the insulating MBL state. One important challenge here is to understand the transition from a delocalized phase to the MBL phase as the disorder strength is increased. As the notion of temperature itself gets blurred, I will describe a novel method to probe ergodicity breaking based on the relaxation of local observables. I would put special emphasis on the relaxation at the MBL critical point where we observe critically slowed dynamics and will comment of the notions of Griffiths phases. If time permits, I will also show some recent results on the observation of a Floquet-MBL phase and on the possibility of MBL in two dimensions using quasi-crystals.

Disorder turns out to be the key ingredient in realizing the insulating MBL state. One important challenge here is to understand the transition from a delocalized phase to the MBL phase as the disorder strength is increased. As the notion of temperature itself gets blurred, I will describe a novel method to probe ergodicity breaking based on the relaxation of local observables. I would put special emphasis on the relaxation at the MBL critical point where we observe critically slowed dynamics and will comment of the notions of Griffiths phases. If time permits, I will also show some recent results on the observation of a Floquet-MBL phase and on the possibility of MBL in two dimensions using quasi-crystals.

Stanford Photonics Research Center Symposium

Monday, September 19, 2016

9:00 am - 4:30 pm

Location: Oshman Hall, McMurtry Building, 355 Roth Way, Stanford, CA 94305, United States

Abstract
Jakob Reichel (Laboratoire Kastler Brossel, ENS/CNRS/UPMC)

SPRC Symposium: Collective Phenomena in Quantum Systems

SPRC Symposium: Collective Phenomena in Quantum Systems

Tuesday, September 20, 2016

11:00 am - 12:30 pm

Location: Oshman Hall, McMurtry Building, 355 Roth Way, Stanford, CA 94305, USA

Abstract
Jonathan Simon (U. Chicago)

SPRC Symposium: Collective Phenomena in Quantum Systems

SPRC Symposium: Collective Phenomena in Quantum Systems

Tuesday, September 20, 2016

11:00 am - 12:30 pm

Location: Oshman Hall, McMurtry Building, 355 Roth Way, Stanford, CA 94305, USA

Abstract
Adi Natan (SLAC)

Self-referenced Coherent Diffractive imaging

Self-referenced Coherent Diffractive imaging

Monday, October 3, 2016

4:00 pm - 5:30 pm

Location: Spilker 232

AbstractTime-resolved femtosecond x-ray diffraction patterns from laser-excited molecular iodine are used to create a movie of intramolecular motion with a temporal and spatial resolution of 30 fs and 0.3 Angstrom. This high fidelity is due to interference between the moving excitation and the unperturbed initial charge distribution. The initial state is used as the local oscillator for heterodyne amplification of the excited charge distribution to retrieve real-space de-novo movies of atomic motion on Angstrom and femtosecond scales. This x-ray interference has not been employed to image atomic motion in molecules before. Coherent vibrational motion and dispersion, dissociation, and rotational dephasing are all clearly visible in the data, thereby demonstrating the stunning sensitivity of heterodyne methods.

Andrei Derevianko (University of Nevada, Reno)

Search for ultralight dark matter with GPS and networks of precision measurement tools

Search for ultralight dark matter with GPS and networks of precision measurement tools

Monday, November 7, 2016

4:00 pm - 5:30 pm

Location: Spilker 232

AbstractCosmological observations indicate that dark matter (DM) constitutes 85% of all matter in the Universe, yet conclusive evidence for DM in terrestrial experiments remains elusive. One of the possibilities is that DM can be composed from ultralight quantum fields whose self-interactions lead to the formation of DM objects in the form of stable topological defects. Such DM ``clumps'', depending on the masses of underlying fields, can be spatially large on the laboratory scale. As the Earth moves through the halo of DM objects, interactions with such DM clumps could lead to measurable variations in GPS signals which propagate through the satellite constellation at galactic velocities of ~ 300 km/s. Here we use the network of atomic clocks onboard GPS satellites as a ~50,000 km aperture DM detector.

By mining over a decade of archival GPS data, we find no evidence for topological defects in the form of domain walls at our current sensitivity, which enables us to improve the present limits on certain DM--ordinary matter coupling strengths by up to six orders of magnitude.

By mining over a decade of archival GPS data, we find no evidence for topological defects in the form of domain walls at our current sensitivity, which enables us to improve the present limits on certain DM--ordinary matter coupling strengths by up to six orders of magnitude.

Ataç İmamoğlu(Institute of Quantum Electronics, ETH Zurich)

Fermi-polarons and polaritons in two dimensional materials

Fermi-polarons and polaritons in two dimensional materials

Friday, November 18, 2016

4:15 pm - 5:15 pm

Location: Spilker 232

AbstractCavity-polaritons have emerged as an exciting platform for studying interacting bosons in a

driven-dissipative setting. Typically, the experimental realization of exciton-polaritons is based

on undoped GaAs quantum wells (QW) embedded in between two monolithic distributed Bragg

reflector (DBR) layers. Introduction of a degenerate electron gas either to the QW hosting

the excitons or a neighboring layer substantially enriches the physics due to polariton-electron

coupling. It has been proposed that such an interacting Bose-Fermi mixture can be used to

study polariton-mediated superconductivity in a two dimensional electron gas.

Transition metal dichalcogenide (TMD) monolayers, such as molybdenum diselenide (MoSe2),

represent a new class of valley semiconductors exhibiting novel features such as strong Coulomb interactions, finite exciton Berry curvature with novel optical signatures and locking of spin and valley degrees of freedom due to large spin-orbit coupling. In contrast to quantum wells or two-dimensional electron systems in III-V semiconductors, TMD monolayers exhibit an ultra-large exciton binding energy of order 500 meV and strong trion peaks in photoluminescence that are red-shifted from the exciton line by 30 meV. In this talk, he will present cavity spectroscopy of gate-tunable monolayer MoSe2 and show that in the limit of perturbative cavity coupling elementary optical excitations in this system are attractive and repulsive exciton-polarons - excitons dressed by Fermi sea electron-hole pairs. By reducing the cavity length, they reach the strong-coupling limit of cavity-QED and observe polariton formation in both attractive and repulsive branches: this constitutes a new regime of polaron physics where the polariton impurity mass is much smaller than that of the itinerant electrons. Their findings constitute a first step in investigation of a new class of degenerate Bose-Fermi mixtures consisting of polaritons and electrons.

driven-dissipative setting. Typically, the experimental realization of exciton-polaritons is based

on undoped GaAs quantum wells (QW) embedded in between two monolithic distributed Bragg

reflector (DBR) layers. Introduction of a degenerate electron gas either to the QW hosting

the excitons or a neighboring layer substantially enriches the physics due to polariton-electron

coupling. It has been proposed that such an interacting Bose-Fermi mixture can be used to

study polariton-mediated superconductivity in a two dimensional electron gas.

Transition metal dichalcogenide (TMD) monolayers, such as molybdenum diselenide (MoSe2),

represent a new class of valley semiconductors exhibiting novel features such as strong Coulomb interactions, finite exciton Berry curvature with novel optical signatures and locking of spin and valley degrees of freedom due to large spin-orbit coupling. In contrast to quantum wells or two-dimensional electron systems in III-V semiconductors, TMD monolayers exhibit an ultra-large exciton binding energy of order 500 meV and strong trion peaks in photoluminescence that are red-shifted from the exciton line by 30 meV. In this talk, he will present cavity spectroscopy of gate-tunable monolayer MoSe2 and show that in the limit of perturbative cavity coupling elementary optical excitations in this system are attractive and repulsive exciton-polarons - excitons dressed by Fermi sea electron-hole pairs. By reducing the cavity length, they reach the strong-coupling limit of cavity-QED and observe polariton formation in both attractive and repulsive branches: this constitutes a new regime of polaron physics where the polariton impurity mass is much smaller than that of the itinerant electrons. Their findings constitute a first step in investigation of a new class of degenerate Bose-Fermi mixtures consisting of polaritons and electrons.

John Kitching (NIST)

Chip-scale Atomic Devices: Miniature Precision Instruments using Atoms, Lasers and MEMS

Chip-scale Atomic Devices: Miniature Precision Instruments using Atoms, Lasers and MEMS

Monday, December 5, 2016

4:00 pm - 5:00 pm

Location: Spilker 232

AbstractWe describe recent work at NIST to develop precision instruments based on atomic spectroscopy, advanced semiconductor lasers and micro-electro-mechanical systems (MEMS). These millimeter-scale instruments achieve take their high stability or sensitivity from the use of atomic spectroscopy, but have considerably reduced power consumption and potentially reduced manufacturing cost compared to their larger counterparts. Physics packages for atomic frequency references with fractional frequency stabilities in the range of 10-11 over one hour have been demonstrated. Using similar device designs and processing, magnetometers with sensitivities below 10 fT/Hz have been demonstrated, making them competitive with commercial SQUID-based sensors without the need for cryogenic cooling. The design, fabrication and performance of these instruments will be described, as well as a number of applications to which the devices are well-suited. Finally, we speculate on possible future directions for chip-scale atomic instrumentation with a focus on the use of laser-cooled atomic samples and tools for fundamental metrology.

Biography

Dr. John Kitching received his PhD. in Applied Physics from the California Institute of Technology in 1995. Since 2003, he has been a physicist in the Time and Frequency Division at NIST and currently is the Leader of the Atomic Devices and Instrumentation Group in NIST’s Physical Measurements Laboratory. His research interests include miniaturized atomic clocks and sensors and applications of semiconductor lasers and micromachining technology to problems in atomic physics and frequency control. Most recently, he and his group pioneered the development of microfabricated “chip-scale” atomic devices for use as frequency references, magnetometers and other sensors. He is a Fellow of NIST and has received a number of awards for his work including the Department of Commerce Silver and Gold Medals, the 2015 IEEE Sensors Council Technical Achievement Award, the 2016 IEEE-UFFC Rabi Award and the prestigious 2013 Rank Prize. He has published over 80 papers in refereed journals, has given numerous invited and plenary talks and has been awarded six patents.

Biography

Dr. John Kitching received his PhD. in Applied Physics from the California Institute of Technology in 1995. Since 2003, he has been a physicist in the Time and Frequency Division at NIST and currently is the Leader of the Atomic Devices and Instrumentation Group in NIST’s Physical Measurements Laboratory. His research interests include miniaturized atomic clocks and sensors and applications of semiconductor lasers and micromachining technology to problems in atomic physics and frequency control. Most recently, he and his group pioneered the development of microfabricated “chip-scale” atomic devices for use as frequency references, magnetometers and other sensors. He is a Fellow of NIST and has received a number of awards for his work including the Department of Commerce Silver and Gold Medals, the 2015 IEEE Sensors Council Technical Achievement Award, the 2016 IEEE-UFFC Rabi Award and the prestigious 2013 Rank Prize. He has published over 80 papers in refereed journals, has given numerous invited and plenary talks and has been awarded six patents.

Cindy Regal (University of Colorado, Boulder)

Improving broadband displacement detection via correlations with a mechanical membrane

Improving broadband displacement detection via correlations with a mechanical membrane

Monday, January 9, 2017

4:00 pm - 5:30 pm

Location: Spilker 232

AbstractThe pursuit of increasingly sensitive interferometric measurement of mechanical motion has a rich history. This pursuit has resulted in the development and study of seminal ideas on quantum limits of measurement and how to improve measurements in the face of seeming limitations. In recent years, an interesting class of devices has been developed in which low-mass, high-frequency, and mechanically isolated objects are coupled to optical cavities. The large response of these mechanical objects to applied forces makes them an ideal platform to observe the effects of radiation forces. We can now cool mechanical membranes well into their quantum ground state and routinely observe the effect of a fluctuating radiation pressure force due to optical shot noise. Our recent measurements study a technique to improve interferometric displacement detection known as variational readout.

Emine Altuntas (Yale University)

Monday, February 6, 2017

4:00 pm - 5:30 pm

Location: Spilker 232

Gerry Gabrielse (Harvard University)

Hofstadter Lecture

Hofstadter Lecture

Monday, February 27, 2017

8:00 pm - 10:00 pm

Location: Hewlett Teaching Center, Rm. 200

AbstractTrapped antimatter particles and atoms open the way to extremely precise comparisons of antimatter and matter - made to test the most fundamental symmetry of the Standard Model.

Naceur Gaalou (Institut für Quantenoptik)

Quantum tests of fundamental physics theories in micro-gravity and space

Quantum tests of fundamental physics theories in micro-gravity and space

Monday, March 6, 2017

4:00 pm - 5:30 pm

Location: Spilker 232

AbstractAtom interferometry in microgravity promises a major leap in improving precision and accuracy of matter-wave sensors [1]. When taking advantage of the unique space environment, fundamental tests challenging the state-of-the-art can be performed using quantum gases systems.

In this talk, we report on our recent progress in devising atom interferometery experiments to test Einstein’s equivalence principle at the 10-15 level or better [2] and detecting gravitational waves with high accuracy. Satellite mission scenarios achieving these goals will be presented.

The use of cold atoms as a source for such sensors poses; however, intrinsic challenges mainly linked to the samples size and mixture dynamics in case of a dual-atomic test. Proposals to mitigate leading systematics in projects involving extensive interferometry times are discussed in this talk as well. Novel methods of quantum engineering at lowest energy scales developed within the droptower experiments and sounding rocket missions are presented in this context [3-6].

References

[1] N. Gaaloul, et al. Proceedings of the International School of Physics "Enrico Fermi" Volume 188 (2014).

[2] D. N. Aguilera et al., Class. Quantum Grav. 31, 115010 (2014).

[3] T. van Zoest et al., Science 328, 1540 (2010).

[4] H. Müntinga et al., Phys. Rev. Lett. 110, 093602 (2013).

[5] J. Rudolph et al. New J. Phys. 17, 079601 (2015).

[6] S. Abend et al. Phys. Rev. Lett. 117, 203003 (2016).

Biography

Naceur Gaaloul is a researcher at the Institute of Quantum Optics, Leibniz University of Hanover, Germany since 2008 when he joined the group of Ernst Rasel and Wolfgang Ertmer. After an advanced diploma in fundamental physics in 2003, he moved to University Paris-sud where he pursued master and doctoral studies. In 2007, he obtained a doctoral title with a research thesis on theoretical manipulation of cold atoms with laser light. His main research focus at the moment is on dynamics of quantum gases in extended time offered by micro-gravity platforms. He is involved in several German, European and international space missions aiming to test fundamental theories of physics by performing atom interferometry experiments.

In this talk, we report on our recent progress in devising atom interferometery experiments to test Einstein’s equivalence principle at the 10-15 level or better [2] and detecting gravitational waves with high accuracy. Satellite mission scenarios achieving these goals will be presented.

The use of cold atoms as a source for such sensors poses; however, intrinsic challenges mainly linked to the samples size and mixture dynamics in case of a dual-atomic test. Proposals to mitigate leading systematics in projects involving extensive interferometry times are discussed in this talk as well. Novel methods of quantum engineering at lowest energy scales developed within the droptower experiments and sounding rocket missions are presented in this context [3-6].

References

[1] N. Gaaloul, et al. Proceedings of the International School of Physics "Enrico Fermi" Volume 188 (2014).

[2] D. N. Aguilera et al., Class. Quantum Grav. 31, 115010 (2014).

[3] T. van Zoest et al., Science 328, 1540 (2010).

[4] H. Müntinga et al., Phys. Rev. Lett. 110, 093602 (2013).

[5] J. Rudolph et al. New J. Phys. 17, 079601 (2015).

[6] S. Abend et al. Phys. Rev. Lett. 117, 203003 (2016).

Biography

Naceur Gaaloul is a researcher at the Institute of Quantum Optics, Leibniz University of Hanover, Germany since 2008 when he joined the group of Ernst Rasel and Wolfgang Ertmer. After an advanced diploma in fundamental physics in 2003, he moved to University Paris-sud where he pursued master and doctoral studies. In 2007, he obtained a doctoral title with a research thesis on theoretical manipulation of cold atoms with laser light. His main research focus at the moment is on dynamics of quantum gases in extended time offered by micro-gravity platforms. He is involved in several German, European and international space missions aiming to test fundamental theories of physics by performing atom interferometry experiments.

Hui Zhai (Institute for Advanced Study, Tsinghua University)

Interesting Dynamics interplay with Symmetry, Topology and Entropy

Interesting Dynamics interplay with Symmetry, Topology and Entropy

Friday, March 10, 2017

10:00 am - 11:00 am

Location: Astro Physics Building, Room PAB 232

AbstractAbstract: In this talk I will discuss several examples of interesting universal dynamics with quantum simulation. In the first example, I will discuss an expansion dynamics of scale invariant quantum gases in a time-dependent harmonic trap, that displays a discrete temporal scaling symmetry, and we term it as “ the Efimovian expansion”. This dynamics reveals the scaling symmetry and the emergent conformal symmetry of strongly interacting quantum system. In the second example, I will discuss quench dynamics from a topological trivial Chern insulator to a topological nontrivial one, and we show how to extract a quantized value from the quench dynamics, that exactly equals to the topological Chern number of the final Hamiltonian after the quench. In the third example, I will prove a theorem that relates the entropy growth after a quench to the out-of-time-ordered correlation that recently discussed in the content of quantum chaos and holographic duality. This three examples reveal the interplay between quantum dynamics with symmetry, topology and entropy, respectively.

[1] Shujin Deng, Zhe-Yu Shi, Pengpeng Diao, Qianli Yu, Hui Zhai, Ran Qi and Haibin Wu, Science, 353, 371 (2016)

[2] Ce Wang, Pengfei Zhang, Xin Chen, Jinlong Yu and Hui Zhai, arXiv: 1611.03304

[3] Ruihua Fan, Pengfei Zhang, Huitao Shen and Hui Zhai, arXiv: 1608.01914

[4] Jun Li, Ruihua Fan,

[1] Shujin Deng, Zhe-Yu Shi, Pengpeng Diao, Qianli Yu, Hui Zhai, Ran Qi and Haibin Wu, Science, 353, 371 (2016)

[2] Ce Wang, Pengfei Zhang, Xin Chen, Jinlong Yu and Hui Zhai, arXiv: 1611.03304

[3] Ruihua Fan, Pengfei Zhang, Huitao Shen and Hui Zhai, arXiv: 1608.01914

[4] Jun Li, Ruihua Fan,

AMO special group Meeting 2017

Monday, March 13, 2017

12:00 am - 12:00 am

AbstractMarch 13-15, 2017

Olympic Valley, CA

Stanford University Physics Department AMO groups

Prof. Mark Kasevich research group

Prof. Monika Schleier-Smith research group

Prof. Jason Hogan research group

Olympic Valley, CA

Stanford University Physics Department AMO groups

Prof. Mark Kasevich research group

Prof. Monika Schleier-Smith research group

Prof. Jason Hogan research group

Thomas Juffmann ( Laboratoire kastler brossel, ENS, Paris)

Multi-pass microscopy - approaching Heisenberg limited sensitivity in optical and electron microscopy

Multi-pass microscopy - approaching Heisenberg limited sensitivity in optical and electron microscopy

Monday, April 3, 2017

4:00 pm - 5:30 pm

Location: Spilker 232

AbstractThe number of biological macromolecules with a structure solved by cryogenic-electron microscopy (cryo-EM) increases dramatically each year. However, many small and weakly scattering protein structures remain out of reach, as electron dose induced specimen damage limits the achievable spatial resolution [1].

Improved sensitivity and spatial resolution can be obtained employing quantum measurement strategies. A quantum optimal approach to measuring small phase shifts, as induced by a thin protein, is to pass each probe particle through the specimen multiple times [2].

Employing self-imaging cavities, this idea can be applied to widefield microscopy [3]. We show post-selected optical birefringence and absorption measurements beyond the shot-noise limit and discuss the applicability of multi-pass microscopy to cryo-EM. Our EM simulations [4] show that multi-pass TEM allows for a tenfold damage reduction in imaging small proteins.

[1] Glaeser et al, Nat. Methods, 13, 1, 28-32 (2016).

[2] Giovannetti et al., Physical Review Letters 96, 10401 (2006).

[3] Juffmann et al, Nature Communications 7, 12858 (2016).

[4] Juffmann et al, arXiv:1612.04931 (2016).

Improved sensitivity and spatial resolution can be obtained employing quantum measurement strategies. A quantum optimal approach to measuring small phase shifts, as induced by a thin protein, is to pass each probe particle through the specimen multiple times [2].

Employing self-imaging cavities, this idea can be applied to widefield microscopy [3]. We show post-selected optical birefringence and absorption measurements beyond the shot-noise limit and discuss the applicability of multi-pass microscopy to cryo-EM. Our EM simulations [4] show that multi-pass TEM allows for a tenfold damage reduction in imaging small proteins.

[1] Glaeser et al, Nat. Methods, 13, 1, 28-32 (2016).

[2] Giovannetti et al., Physical Review Letters 96, 10401 (2006).

[3] Juffmann et al, Nature Communications 7, 12858 (2016).

[4] Juffmann et al, arXiv:1612.04931 (2016).

Immanuel Bloch (Max Planck Institute of Quantum Optics)

Controlling and Exploring Quantum Matter Using Ultracold Atoms in Optical Lattices

Controlling and Exploring Quantum Matter Using Ultracold Atoms in Optical Lattices

Tuesday, April 11, 2017

4:30 pm - 6:00 pm

Location: Hewlett Teaching Center, room 200 Physics/AP Colloquium

AbstractMore than 30 years ago, Richard Feynman outlined the visionary concept of a quantum simulator for carrying out complex physics calculations. Today, his dream has become a reality in laboratories around the world. In my talk I will focus on the remarkable opportunities offered by ultracold quantum gases trapped in optical lattices to address fundamental physics questions ranging from condensed matter physics over statistical physics to high energy physics with table-top experiment.

For example, I will show how it has now become possible to image and control quantum matter with single atom sensitivity and single site resolution, thereby allowing one to directly image individual quantum fluctuations of a many-body system, to directly reveal antiferromagnetic order in the fermionic Hubbard model or hidden ‘topological order’. I will also show, how recent experiments with cold gases in optical lattices have enabled to realise and probe artificial magnetic fields that lie at the heart of topological energy bands in a solid, including Thouless charge pumps in multiple dimensions. Finally, I will discuss our recent experiments on novel many-body localised states of matter that challenge our understanding of the connection between statistical physics and quantum mechanics at a fundamental level.

For example, I will show how it has now become possible to image and control quantum matter with single atom sensitivity and single site resolution, thereby allowing one to directly image individual quantum fluctuations of a many-body system, to directly reveal antiferromagnetic order in the fermionic Hubbard model or hidden ‘topological order’. I will also show, how recent experiments with cold gases in optical lattices have enabled to realise and probe artificial magnetic fields that lie at the heart of topological energy bands in a solid, including Thouless charge pumps in multiple dimensions. Finally, I will discuss our recent experiments on novel many-body localised states of matter that challenge our understanding of the connection between statistical physics and quantum mechanics at a fundamental level.

Ehud Altman (UC Berkeley)

Quantum thermalization and many-body localization: new insights from theory and experiments with ultra-cold atoms

Quantum thermalization and many-body localization: new insights from theory and experiments with ultra-cold atoms

Monday, May 1, 2017

4:00 pm - 5:30 pm

Location: Spilker 232

AbstractRecent theoretical work has uncovered surprising richness in the dynamics of strongly interacting quantum systems, defining new classes of dynamics ranging from many-body localization to maximally chaotic behavior. This progress has highlighted fundamental open questions including, for example, the nature of the many body localization phase transition as well as the relation between quantum chaos and hydrodynamic modes in thermalizing systems. In this talk I will focus on how experiments with ultra-cold atoms can help address some of these questions. First, I will review recent progress in confronting the emerging theoretical picture of the MBL phase and phase transition with experimental tests. Then, I will turn to describe a new approach to compute the long time dynamics of thermalizing systems using tensor networks, allowing to compute both hydrodynamic transport properties and characteristics of quantum chaos. I will discuss proposals to test these results in experiments.

Nathalie De Leon (Princeton University)

Physics/AP Colloquium

Physics/AP Colloquium

Tuesday, May 23, 2017

4:30 pm - 6:00 pm

Location: Hewlett Teaching Center, Rm. 200

Michel Devoret (Yale University)

Physics/AP Colloquium

Physics/AP Colloquium

Tuesday, May 30, 2017

4:30 pm - 6:00 pm

Location: Hewlett Teaching Center, Rm. 200

Christian Gross (Max Planck Institute of Quantum Optics)

Quantum Gas Microscopes - From Textbook Experiments to New Frontiers

Quantum Gas Microscopes - From Textbook Experiments to New Frontiers

Monday, June 5, 2017

4:00 pm - 5:30 pm

Location: Spilker 232

AbstractUltracold quantum gases in optical lattices provide a unique platform for the study of tailored many-body systems. The realization of quantum gas microscopes marked a new era in this field. They enabled the precision detection of single atoms on individual lattice sites and with this provide direct experimental access to non-local correlation functions. Here we summarize the experimental progress with this new platform, where experiments evolved from textbook like studies in conceptually simple settings towards precisely controlled studies in computationally inaccessible regimes. We discuss recent results on many-body localization in two dimensions as well as on string correlations in Fermi-Hubbard chains.

Frédéric Chevy (Laboratoire Kastler Brossel)

Dual superfluidity in ultracold Bose-Fermi mixtures

Dual superfluidity in ultracold Bose-Fermi mixtures

Monday, June 12, 2017

10:30 am - 11:30 am

Location: PAB 232

AbstractReaching dual superfluidity in helium mixtures has long been one of low-temperature physics holy grails . However, this long sought goal has been thwarted by the repulsive interactions between the two isotopes that leads to their demixion at low temperature. In ultracold atoms, the possibility offered by Feshbach resonances of tuning the strength of interatomic interactions has allowed us to cool a mixture of 6Li and 7Li into a regime where the mixture is stable and both species are superfluid. We have proved their superfluid behaviour by creating a counterflow between the two species. We have demonstrated the existence suggesting the existence of a novel damping mechanism generalizing Landau's scenario to superfluid mixtures.

More recently, we have shown that probing the inelastic decay of the mixture could be used as a quantitative probe of the short range correlation of a many-body system.

More recently, we have shown that probing the inelastic decay of the mixture could be used as a quantitative probe of the short range correlation of a many-body system.