Stanford Advisors


All Publications


  • An optical lattice with sound. Nature Guo, Y., Kroeze, R. M., Marsh, B. P., Gopalakrishnan, S., Keeling, J., Lev, B. L. 2021; 599 (7884): 211-215

    Abstract

    Quantized sound waves-phonons-govern the elastic response of crystalline materials, and also play an integral part in determining their thermodynamic properties and electrical response (for example, by binding electrons into superconducting Cooper pairs)1-3. The physics of lattice phonons and elasticity is absent in simulators of quantum solids constructed of neutral atoms in periodic light potentials: unlike real solids, traditional optical lattices are silent because they are infinitely stiff4. Optical-lattice realizations of crystals therefore lack some of the central dynamical degrees of freedom that determine the low-temperature properties of real materials. Here, we create an optical lattice with phonon modes using a Bose-Einstein condensate (BEC) coupled to a confocal optical resonator. Playing the role of an active quantum gas microscope, the multimode cavity QED system both images the phonons and induces the crystallization that supports phonons via short-range, photon-mediated atom-atom interactions. Dynamical susceptibility measurements reveal the phonon dispersion relation, showing that these collective excitations exhibit a sound speed dependent on the BEC-photon coupling strength. Our results pave the way for exploring the rich physics of elasticity in quantum solids, ranging from quantum melting transitions5 to exotic 'fractonic' topological defects6 in the quantum regime.

    View details for DOI 10.1038/s41586-021-03945-x

    View details for PubMedID 34759361

  • Enhancing Associative Memory Recall and Storage Capacity Using Confocal Cavity QED PHYSICAL REVIEW X Marsh, B. P., Guo, Y., Kroeze, R. M., Gopalakrishnan, S., Ganguli, S., Keeling, J., Lev, B. L. 2021; 11 (2)
  • Photon-Mediated Peierls Transition of a 1D Gas in a Multimode Optical Cavity. Physical review letters Rylands, C., Guo, Y., Lev, B. L., Keeling, J., Galitski, V. 2020; 125 (1): 010404

    Abstract

    The Peierls instability toward a charge density wave is a canonical example of phonon-driven strongly correlated physics and is intimately related to topological quantum matter and exotic superconductivity. We propose a method for realizing an analogous photon-mediated Peierls transition, using a system of one-dimensional tubes of interacting Bose or Fermi atoms trapped inside a multimode confocal cavity. Pumping the cavity transversely engineers a cavity-mediated metal-to-insulator transition in the atomic system. For strongly interacting bosons in the Tonks-Girardeau limit, this transition can be understood (through fermionization) as being the Peierls instability. We extend the calculation to finite values of the interaction strength and derive analytic expressions for both the cavity field and mass gap. They display nontrivial power law dependence on the dimensionless matter-light coupling.

    View details for DOI 10.1103/PhysRevLett.125.010404

    View details for PubMedID 32678647

  • Photon-Mediated Peierls Transition of a 1D Gas in a Multimode Optical Cavity PHYSICAL REVIEW LETTERS Rylands, C., Guo, Y., Lev, B. L., Keeling, J., Galitski, V. 2020; 125 (1)
  • Dynamical Spin-Orbit Coupling of a Quantum Gas. Physical review letters Kroeze, R. M., Guo, Y., Lev, B. L. 2019; 123 (16): 160404

    Abstract

    We realize the dynamical 1D spin-orbit coupling (SOC) of a Bose-Einstein condensate confined within an optical cavity. The SOC emerges through spin-correlated momentum impulses delivered to the atoms via Raman transitions. These are effected by classical pump fields acting in concert with the quantum dynamical cavity field. Above a critical pump power, the Raman coupling emerges as the atoms superradiantly populate the cavity mode with photons. Concomitantly, these photons cause a backaction onto the atoms, forcing them to order their spin-spatial state. This SOC-inducing superradiant Dicke phase transition results in a spinor-helix polariton condensate. We observe emergent SOC through spin-resolved atomic momentum imaging and temporal heterodyne measurement of the cavity-field emission. Dynamical SOC in quantum gas cavity QED, and the extension to dynamical gauge fields, may enable the creation of Meissner-like effects, topological superfluids, and exotic quantum Hall states in coupled light-matter systems.

    View details for DOI 10.1103/PhysRevLett.123.160404

    View details for PubMedID 31702345

  • Dynamical Spin-Orbit Coupling of a Quantum Gas PHYSICAL REVIEW LETTERS Kroeze, R. M., Guo, Y., Lev, B. L. 2019; 123 (16)
  • Sign-Changing Photon-Mediated Atom Interactions in Multimode Cavity Quantum Electrodynamics PHYSICAL REVIEW LETTERS Guo, Y., Kroeze, R. M., Vaidya, V. D., Keeling, J., Lev, B. L. 2019; 122 (19): 193601

    Abstract

    Sign-changing interactions constitute a crucial ingredient in the creation of frustrated many-body systems such as spin glasses. We present here the demonstration of a photon-mediated sign-changing interaction between Bose-Einstein-condensed atoms in a confocal cavity. The interaction between two atoms is of an unusual, nonlocal form proportional to the cosine of the inner product of the atoms' position vectors. This interaction arises from the differing Gouy phase shifts of the cavity's degenerate modes. The interaction drives a nonequilibrium Dicke-type phase transition in the system leading to atomic checkerboard density-wave order. Because of the Gouy phase anomalies, the checkerboard pattern can assume either a sinelike or cosinelike character. This state is detected via the holographic imaging of the cavity's superradiant emission. Together with a companion paper [Y. Guo, V. D. Vaidya, R. M. Kroeze, R. A. Lunney, B. L. Lev, and J. Keeling, Emergent and broken symmetries of atomic self-organization arising from Gouy phases in multimode cavity QED, Phys. Rev. A 99, 053818 (2019)PLRAAN2469-992610.1103/PhysRevA.99.053818], we explore this interaction's influence on superradiant phase transitions in multimode cavities. Employing this interaction in cavity QED spin systems may enable the creation of artificial spin glasses and quantum neural networks.

    View details for DOI 10.1103/PhysRevLett.122.193601

    View details for Web of Science ID 000468228200005

    View details for PubMedID 31144918

  • Emergent and broken symmetries of atomic self-organization arising from Gouy phase shifts in multimode cavity QED PHYSICAL REVIEW A Guo, Y., Vaidya, V. D., Kroeze, R. M., Lunney, R. A., Lev, B. L., Keeling, J. 2019; 99 (5)
  • Spinor Self-Ordering of a Quantum Gas in a Cavity. Physical review letters Kroeze, R. M., Guo, Y., Vaidya, V. D., Keeling, J., Lev, B. L. 2018; 121 (16): 163601

    Abstract

    We observe the joint spin-spatial (spinor) self-organization of a two-component Bose-Einstein condensate (BEC) strongly coupled to an optical cavity. This unusual nonequilibrium Hepp-Lieb-Dicke phase transition is driven by an off-resonant Raman transition formed from a classical pump field and the emergent quantum dynamical cavity field. This mediates a spinor-spinor interaction that, above a critical strength, simultaneously organizes opposite spinor states of the BEC on opposite checkerboard configurations of an emergent 2D lattice. The resulting spinor density-wave polariton condensate is observed by directly detecting the atomic spin and momentum state and by holographically reconstructing the phase of the emitted cavity field. The latter provides a direct measure of the spin state, and a spin-spatial domain wall is observed. The photon-mediated spin interactions demonstrated here may be engineered to create dynamical gauge fields and quantum spin glasses.

    View details for DOI 10.1103/PhysRevLett.121.163601

    View details for PubMedID 30387632

  • Spinor Self-Ordering of a Quantum Gas in a Cavity PHYSICAL REVIEW LETTERS Kroeze, R. M., Guo, Y., Vaidya, V. D., Keeling, J., Lev, B. L. 2018; 121 (16)
  • Tunable-Range, Photon-Mediated Atomic Interactions in Multimode Cavity QED PHYSICAL REVIEW X Vaidya, V. D., Guo, Y., Kroeze, R. M., Ballantine, K. E., Kollar, A. J., Keeling, J., Lev, B. L. 2018; 8 (1)
  • Supermode-density-wave-polariton condensation with a Bose-Einstein condensate in a multimode cavity. Nature communications Kollár, A. J., Papageorge, A. T., Vaidya, V. D., Guo, Y., Keeling, J., Lev, B. L. 2017; 8: 14386-?

    Abstract

    Phase transitions, where observable properties of a many-body system change discontinuously, can occur in both open and closed systems. By placing cold atoms in optical cavities and inducing strong coupling between light and excitations of the atoms, one can experimentally study phase transitions of open quantum systems. Here we observe and study a non-equilibrium phase transition, the condensation of supermode-density-wave polaritons. These polaritons are formed from a superposition of cavity photon eigenmodes (a supermode), coupled to atomic density waves of a quantum gas. As the cavity supports multiple photon spatial modes and because the light-matter coupling can be comparable to the energy splitting of these modes, the composition of the supermode polariton is changed by the light-matter coupling on condensation. By demonstrating the ability to observe and understand density-wave-polariton condensation in the few-mode-degenerate cavity regime, our results show the potential to study similar questions in fully multimode cavities.

    View details for DOI 10.1038/ncomms14386

    View details for PubMedID 28211455

    View details for PubMedCentralID PMC5321730