Session C03: Out-of-Equilibrium Trapped Gasses

Live

We report, based on momentum and real space pattern recognition, formation of density patterns with two- ($D_2$), four- ($D_4$) and six-fold ($D_6$) symmetries in Bose-Einstein condensates with atomic interactions driven at two frequencies. The symmetry of the pattern is controlled by the ratio of the frequencies. The D6 density waves, in particular, arise from a resonant wave mixing process that coherently correlates and enhances the excitations that respect the symmetry. Our work provides insight into the origin of pattern formation in quantum systems, while also suggests a new way to generate multi-mode entanglement.   

Live

We propose a protocol for generating spin cat states (also called generalized GHZ states) with ultracold fermionic atoms in 3D optical lattices or optical tweezer arrays. Our method uses on-site interactions, laser driving and harmonic trapping to generate energetic constraints upon the atomic motion. These constraints permit the stepwise transformation of a local two-component superposition into a spatially extended many-body entangled state, by allowing one component to evolve while keeping the other one unchanged. The protocol requires no site-resolved driving lasers, has a generation time linear in the size of the cat, and exhibits robustness to global phase drifts of the drive. Furthermore, it naturally includes a harmonic trap that is otherwise detrimental to many entanglement-generating protocols. The ability to implement this protocol in state-of-the-art tweezer arrays or 3D lattice clocks allows for immediate use of the cat state for metrological improvement beyond the standard quantum limit in real-world sensors.   

Live

We consider two species of hard-core bosons with density dependent hopping in a one-dimensional optical lattice, for which we propose experimental realizations using time-periodic driving. The quantum phase diagram for half-integer filling is determined by combining different advanced numerical simulations with analytic calculations. We find that a reduction of the density-dependent hopping induces a Mott-insulator to superfluid transition. For negative hopping a previously unknown state is found, where one species induces a gauge phase of the other species, which leads to a superfluid phase of gauge-paired particles. The corresponding experimental signatures are discussed.   

Live

Optical lattice experiments are an ideal tool for exploring the interplay among disorder-induced localization, interaction-induced localization, and dynamical localization. We discuss experiments probing the response of a quantum gas in a tunable bichromatic lattice to strong phasonic [1] and dipolar modulation. Independent tuning of the quasi-disorder strength and the effective tunneling enables exploration of a wide parameter space lying between limiting cases such as Aubry-André localization (for zero drive strength) and dynamical localization (for a dipolar drive at zero quasi-disorder strength).   

Live

The kicked rotor is a prototypical testbed for exploring quantum chaos and dynamical localization in single-particle quantum mechanics. We report experiments introducing tunable interactions into an optical-lattice-based quantum kicked rotor. Results probe the existence of a dynamical many-body localized regime, and allow detailed characterization of interaction-driven delocalization in quantum kicked rotors. *The authors acknowledge support from ARO (PECASE W911NF1410154) and NSF (CAREER 1555313)   

Live

Out-of-equilibrium processes can exhibit remarkable universal properties independent of a system’s microscopic details. Here we demonstrate dynamical scaling that has recently been predicted in the context of a non-thermal fix-point.\\ Starting with a weakly interacting Bose gas of $^{39}$K in a homogeneous 3D trapping potential above $T_\mathrm{c}$, we heavily truncate the Bose distribution and observe a self-similar time evolution of the closed quantum system in momentum space while the system relaxes through the BEC phase transition. We experimentally find scaling exponents in the UV and IR, which we compare to recent theoretical predictions. Measurements at different interactions collapse by scaling time with the scattering length.   

Live

Recent work on matter-wave emission from atoms trapped in optical lattices [1] has enabled studies of exotic emission phenomena, including the formation of spatially extended bound states. Their presence has been predicted to give rise to a modification of the Hamiltonian governing the motional dynamics of atoms in the lattice. In this talk, we will discuss our ongoing theoretical and experimental efforts in characterizing the effective tunneling between lattice sites. \newline \newline [1] L. Krinner, M. Stewart, A. Pazmiño, J. Kwon, D. Schneble, Nature 559, 589–592 (2018)   

On Demand

The momenta of the quasi-particles that emerge from interactions in many-body integrable quantum systems are referred to as the rapidities. Recently, we reported the first ever measurement of a distribution of rapidities by looking at the asymptotic momentum distribution after quenching an initially trapped Tonks-Girardeau (T-G) gas to a flat potential and letting the atoms expand [1]. Here, we extend our study of rapidities. We quench 1D Bose gases in both the strong and intermediate coupling regimes from an initial trap to a much deeper trap. After a variable evolution time in the deeper trap we perform rapidity measurements by suddenly turning off the trap. Unlike the momentum distributions after such a quench, which change shape as the gas undergoes a breathing oscillation, the rapidity distributions in the first period of oscillation is shown to evolve self-similarly. We compare our measurements to generalized hydrodynamics calculations. [1] J. M. Wilson, N. Malvania, Y. Le, Y. Zhang, M. Rigol, and D. S. Weiss, arXiv:1908.05364 (to appear in Science).   

On Demand

Magnetic Feshbach resonances are a powerful tool in order to control the scattering length in ultracold gas experiments [1], but are limited to given atomic species or applied magnetic field strengths. Recent studies showed that periodic driving can also induce scattering resonances, but are limited to the simplest inter-particle potentials [2-4]. In this work we consider a more realistic inter-atomic interaction by including an open and a closed channel, as they occur in the description of magnetic Feshbach resonances [5]. We allow for a time-periodic modulation of the inter-channel coupling or the detuning of the channel thresholds and report about the emergence of driving induced scattering resonances. A detailed investigation how resonance frequency and width depend on both driving frequency and strength is performed. With this we obtain predictions for a time-periodic modulation of the magnetic field near a magnetic Feshbach resonance, which are of experimental interest. [1] C. Chin et al., Rev. Mod. Phys. 82, 1225 (2010) [2] D.H. Smith, Phys. Rev. Lett. 115, 193002 (2015) [3] A.G. Sykes et al., Phys. Rev. A 95, 062705 (2017) [4] S.A. Reyes et al., New J. Phys. 19, 043029 (2017) [5] R.A. Duine and H.T.C. Stoof, Phys. Rep. 396, 115 (2004)   

On Demand

We experimentally investigate a driven-dissipative Josephson junction array, realized with a weakly interacting Bose-Einstein condensate loaded in a 1-D optical lattice. Tunneling from the neighboring sites makes up the driving force. Engineered losses on one site act as a local dissipative process. The source of these losses is an electron beam, which we also use to image the system (SEM) and monitor the losses. Decreasing the tunnel coupling or increasing the dissipation strength makes the system cross from a superfluid to a resistive state. For intermediate values, the system shows bistable behavior, with coexistence of a superfluid and an incoherent branch. Studying single experimental runs, we see the filling of the lossy site change from the resistive to the superfluid state within a few tunneling times. We explore the hysteresis of the system as a function of sweep time, temperature and initial atom number. Studying the dynamics towards a steady state averaged over many experimental runs, we find a critical slowing down accompanied by large-scale quantum fluctuations. Our results reveal the presence of a first order dissipative phase transition in the system.