Bulletin of the American Physical Society
48th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 62, Number 8
Monday–Friday, June 5–9, 2017; Sacramento, California
Session M2: Cavity QED with Ultracold AtomsFocus

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Chair: Monika SchleierSmith, Stanford University Room: 306307 
Thursday, June 8, 2017 8:00AM  8:30AM 
M2.00001: Quantum Crystals of Matter and Light Invited Speaker: Tobias Donner The coupling of a quantum gas to the field of an optical highfinesse cavity can be employed to induce globalrange atomatom interactions. If these are sufficiently strong, such a manybody system undergoes a structural phase transition. Introducing a 3D optical lattice to this system, the collisional shortrange interactions can be brought to competition with these globalrange interactions and – at the same time – with the zeropoint motion of the particles. We explore a rich phase diagram hosting four distinct phases – a superfluid, a lattice supersolid, a Mott insulator and a charge density wave. In a different experiment, we couple a superfluid cloud of atoms simultaneously to two intersecting optical cavities. This arrangement leads to symmetry enhancement and the resulting system exhibits a continuous spatial U(1)symmetry. The combination of two continuous symmetries – the gauge symmetry of the superfluid and the spatial symmetry – is a prerequisite for a supersolid state of matter, which we explore in our experiments. [Preview Abstract] 
Thursday, June 8, 2017 8:30AM  9:00AM 
M2.00002: Quantum Manybody Physics with Multimode Cavity QED Invited Speaker: Benjamin Lev Phase transitions, where observable properties of a manybody system change discontinuously, can occur in both open and closed systems. Ultracold atoms have provided an exemplary model system to demonstrate the physics of closedsystem phase transitions, confirming many theoretical models and results. Our understanding of dissipative phase transitions in quantum systems is less developed, and experiments that probe this physics even less so. 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. We will report our observation of a novel form of nonequilibrium~phase transition, the condensation of supermodedensitywavepolaritons. These polaritons are formed from a hybrid ``supermode" of cavity photons coupled to atomic density waves of a quantum gas. These results, found in the fewmodedegenerate cavity regime, demonstrate the potential of fully multimode cavities to exhibit physics beyond meanfield theories, possibly in the presence of dynamic synthetic gauge fields. Such systems will provide experimental access to nontrivial phase transitions in driven dissipative quantum systems as well as enabling the studies of novel nonequilibrium spin glasses and neuromorphic computation. [Preview Abstract] 
Thursday, June 8, 2017 9:00AM  9:12AM 
M2.00003: Supersolidity and tunable symmetries with ultracold atoms in optical cavities Philip Zupancic, Julian Leonard, Andrea Morales, Tilman Esslinger, Tobias Donner By coupling a BoseEinstein condensate to two optical cavities we gain experimental access to new phases of matter. For large detuning of the cavities from the atomic resonance, the combination of selforganisation processes with $\mathbb{Z}_2$ symmetry in each cavity gives rise to one enhanced U(1) symmetry that corresponds to translational invariance of the atoms in one direction. We report on the observation of a phase transition to a supersolid state that breaks this continuous symmetry, and show spectroscopic measurements of the NambuGoldstone and Higgs modes present in this phase. The light fields leaking from the cavities enable realtime surveillance of the system dynamics. Approaching the atomic resonance, the continuous invariance is lifted as cavitycavity coupling comes into play. [Preview Abstract] 
Thursday, June 8, 2017 9:12AM  9:24AM 
M2.00004: Emergent equilibrium in manybody optical bistability Michael FossFeig, Pradeep Niroula, Jeremy Young, Mohammad Hafezi, Alexey Gorshkov, Ryan Wilson, Mohammad Maghrebi Manybody systems constructed of quantumoptical building blocks can now be realized in experimental platforms ranging from excitonpolariton fluids to Rydberg gases, establishing a fascinating interface between traditional manybody physics and the nonequilibrium setting of cavityQED. At this interface the standard intuitions of both fields are called into question, obscuring issues as fundamental as the role of fluctuations, dimensionality, and symmetry on the nature of collective behavior and phase transitions. We study the drivendissipative BoseHubbard model, a minimal description of atomic, optical, and solidstate systems in which particle loss is countered by coherent driving. Despite being a lattice version of optical bistabilitya foundational and patently nonequilibrium model of cavityQEDthe steady state possesses an emergent equilibrium description in terms of an Ising model. We establish this picture by identifying a limit in which the quantum dynamics is asymptotically equivalent to nonequilibrium Langevin equations, which support a phase transition described by model A of the HohenbergHalperin classification. Simulations of the Langevin equations corroborate this picture, producing results consistent with the behavior of a finitetemperature Ising model. [Preview Abstract] 
Thursday, June 8, 2017 9:24AM  9:36AM 
M2.00005: Observation of dynamic instability from coherent coupling of atomic motion and spin ~ Justin Gerber, Jonathan Kohler, Emma Dowd, Dan StamperKurn The collective spin precession of an atomic ensemble about an applied magnetic field can be approximated by the dynamics of a negative mass harmonic oscillator when the spin precesses close to its highest energy state. The amplitude of a negative mass oscillator increases as it loses energy meaning that when a negative mass oscillator is coupled to a positive mass oscillator the system undergoes an instability in which, through a cascade of nearresonant pair creation processes, the amplitude of each oscillator grows exponentially. We have experimentally realized this instability by using the field of an optical cavity to coherently couple the collective spin and mechanical degrees of freedom of an atomic ensemble. We demonstrate control of this instability by tuning the parameters of the coupled system. [Preview Abstract] 
Thursday, June 8, 2017 9:36AM  9:48AM 
M2.00006: Observation of twomode thermal squeezing through coherent coupling of positive and negativemass oscillators Jonathan Kohler, Justin Gerber, Emma Dowd, Dan StamperKurn Measurement and control of either the mechanical or rotational degrees of freedom of an atomic ensemble have been well demonstrated through coupling to an optical cavity. We have previously used autonomous cavity feedback to demonstrate the stabilization of a precessing collective spin near its highenergy stationary state, where excitations away from this state evolve like an effective negativemass oscillator. When the dynamics of this negativemass mode are coherently coupled to the collective atomic motion, we observe a parametric instability, which leads to the spontaneous amplification of a correlated mode of the hybrid system. Under the correct conditions, this interaction drives the system into a twomode squeezed state. I will present the latest results of our measurements of the correlations created through this process. [Preview Abstract] 
Thursday, June 8, 2017 9:48AM  10:00AM 
M2.00007: Rydberg Polariton Blockade in a 0D Photonic Quantum Dot Ningyuan Jia, Nathan Shine, Alex Georgakopoulos, Albert Ryou, Ariel Sommer, Jonathan Simon Rydberg electromagnetically induced transparency (rEIT) is an emerging approach to mediate strong interactions between individual optical photons. To date, experimental investigations of this physics have employed freely propagating lightfields coupled to Rydbergdressed atomic ensembles. Here we enhance the lightmatter coupling by trapping the light field within an optical resonator, providing the photons with more time to interact with one another, and requiring substantially lower densities of cold atoms. Furthermore, working with a nondegenerate optical resonator allows us to directly realize a blockaded 0dimensional photonic quantum dot whose properties we then explore. We observe a spectrally narrow darkpolariton resonance up to extremelyhigh Rydberg states (n\textasciitilde 121), and demonstrate strong photonphoton interactions within the dot through strong blockade of cavity transmission, demonstrated through antibunching of the transmitted field. By combining this breakthrough with degeneratecavity realizations of tunable 2D photonic puddles that we have developed in parallel, this work points the way to explorations of crystalline and topological quantum materials composed of cavity Rydberg polaritons. [Preview Abstract] 
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