Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session Q33: NonEquilibrium Physics with Cold Atoms and Molecules, Rydberg Gases, and Trapped Ions IIIFocus Recordings Available

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Sponsoring Units: DAMOP DCMP Chair: Padetha Tin, NASA Glenn Research Center Room: McCormick Place W192C 
Wednesday, March 16, 2022 3:00PM  3:12PM 
Q33.00001: Accurate modeling of single quantum system dynamics under the truncated Wigner approximation Justin Provazza Theoretical modeling of the dynamics of open quantum systems remains a notoriously challenging endeavor. Existing dynamical methods typically treat interactions between quantum systems and their environment at the ensemble level and/or implicitly project out environmental degreesoffreedom. Here, we present a nonadiabatic quantum dynamics formulation that relaxes these assumptions and, in contrast to the aforementioned class of methods, provides access to the dynamical interaction of single quantum systems with their environment. This formulation is based on the truncated Wigner approximation combined with a perturbative series describing transitions between quantum states. Whereas other approaches capable of describing single ensemble members exist, this method uniquely allows for a systematic improvement of accuracy up to the exact answer. We show that, even for challenging test cases, this method converges rapidly, making for an efficient simulation tool for studying single quantum system phenomena. 
Wednesday, March 16, 2022 3:12PM  3:24PM 
Q33.00002: Entanglement generation in the drivendissipative Ising model Daniel Paz, Arghavan SafaviNaini, Mohammad Maghrebi Quantum entanglement is a resource for quantum information processing. However, generating manybody entangled states robustly is hard. Drivendissipative platforms can be used to generate these states in the nonequilibrium steady state. In this talk, we discuss various entanglement features of the drivendissipative Ising model, a descendant of the paradigmatic open Dicke model. Using an exact formalism as well as numerical simulation, we identify the von Neumann entropy, logarithmic negativity, and the quantum Fisher information all throughout the phase diagram. We find that the von Neumann entropy diverges logarithmically with the system size at the phase transition, while the logarithmic negativity remains constant. For the quantum Fisher information, we show that the optimal direction of the spin operator at criticality is determined exactly by the soft mode, and is given exactly by F = 2N for a system size N. This integer value suggests that the steady state at criticality is a product of 2particle GHZ states in the basis of the soft mode operator. Finally we show that, within the ordered phase and for relatively small dissipation, the quantum Fisher information grows beyond this bound, indicating that the system becomes highly entangled. 
Wednesday, March 16, 2022 3:24PM  3:36PM 
Q33.00003: Seeding Crystallization in Time Sai Vinjanampathy, Michal Hajdušek, Rosario Fazio, Parvinder Solanki We introduce the concept of seeding of crystallization in time by studying the dynamics of an ensemble of coupled continuous time crystals. We demonstrate that a single subsystem in the brokensymmetry phase acting as a nucleation center may induce timetranslation symmetry breaking across the entire ensemble. The seeding effect is observed for both coherent as well as dissipative coupling, and for a broad range of parameter regimes. In the spirit of mutual synchronization, we investigate the dynamics where all subsystems are in the broken symmetry phase. We observe that more broadly detuned time crystals require weaker coupling strength in order for synchronization to occur. This is in contrast to basic knowledge from classical as well as quantum synchronization theory. We show that this surprising observation is a direct consequence of the seeding effect. 
Wednesday, March 16, 2022 3:36PM  3:48PM 
Q33.00004: Effect of spin fluctuations in ultracold bosons coupled to dynamical Z_{2}gauge fields Yuma Watanabe, Shohei Watabe, Tetsuro Nikuni We study the Z_{2} BoseHubbard model [1] that describes a strongly correlated bosonic system coupled to lattice degrees of freedom. This model has been proposed to describe spatial modulation of the hopping. The lattice degrees of freedom are introduced due to the Z_{2} gauge field, which is incorporated into the BoseHubbard model by placing spins on links between neighboring sites. In the case where spin fluctuations are negligible, this model exhibits the structural phase transition with the translational symmetry breaking[1]. By using the densitymatrix renormalization method in matrixproduct state form [2], we elucidate the effect of spin fluctuations on the phase diagram of the Z_{2} Bose Hubbard model. We investigate the phase diagram that includes the diabatic regimes in which spin fluctuations cannot be ignored, and study the effect of spin fluctuations on ground states. 
Wednesday, March 16, 2022 3:48PM  4:00PM 
Q33.00005: Enhanced sensing of anharmonic perturbations in a dissipatively coupled antiPT symmetric system. Jayakrishnan Muttathil Prabhakarapada Nair, Debsuvra Mukhopadhyay, Girish S Agarwal Recently, nonHermitian degeneracies known as exceptional points have unravelled a new direction to administer enhanced response in open quantum systems. However, most research activity based on exceptional points requires paritytime (PT) symmetry with a balanced gainloss profile, and they are tailormade to sense linear perturbations. But, physical systems are inherently anharmonic, and nonlinear models most accurately describe macroscopic physics. 
Wednesday, March 16, 2022 4:00PM  4:12PM 
Q33.00006: Twoparticle States in Onedimensional Coupled BoseHubbard Models Yabo Li, Dominik Schneble, TzuChieh Wei We study doubly coupled BoseHubbard models and solve for the wave functions and energies of twoparticle eigenstates. Even though the wave functions do not directly follow the form of a Bethe Ansatz, we describe an intuitive construction to express them as combinations of ChoyHaldane states for models with intra and interspecies interaction. Our results show that the twoparticle spectrum of the system comprises in general 4 different continua and 3 doublon dispersions with different interactions. Their energies vary with interaction strengths. The existence of doublons depends on the coupling strength between two species of bosons. We analyze one specific limit, i.e. with infinite interaction, and show the spectrum for all types of twoparticle states and their spatial and entanglement properties. 
Wednesday, March 16, 2022 4:12PM  4:48PM 
Q33.00007: Exact results for nonequilibrium ultracold matter Invited Speaker: Kaden R Hazzard Quantum manybody dynamics raise fertile scientific questions, for example about thermalization, entanglement generation, and classical simulability. These questions are explored in a variety of experiments with ultracold matter, but they resist theory: semianalytic methods can fail to capture the essential physics, and numerical methods are often impossible to convincingly converge. Exact results are jewels: illuminating and beautiful, but rare. 
Wednesday, March 16, 2022 4:48PM  5:00PM 
Q33.00008: Missing Rung Problem in Vibrational Ladder Climbing Takahiro Horiba, Hirotoshi Hirai, Soichi Shiral We observed vanishing of the transition dipole moment, interrupting vibrational ladder climbing (VLC) in molecular systems. We clarified the mechanism of this phenomenon and present a method to use an additional chirped pulse to preserve VLC. To show the effectiveness of our method, we conducted wavepacket dynamics simulations for LiH dissociations with chirped pulses. The results indicate that the efficiency of LiH dissociation is significantly improved by our method compared to conventional methods. We also revealed the quantum interference effect behind the excitation process of VLC. 
Wednesday, March 16, 2022 5:00PM  5:12PM 
Q33.00009: Selfordered Time Crystals: Periodic Temporal Order under Quasiperiodic Driving Sayan Choudhury, W.Vincent Liu A discrete time crystal is a remarkable nonequilibrium phase of matter characterized by persistent subharmonic response to a periodic drive. Motivated by the question of whether such timecrystalline order can persist when the drive becomes aperiodic, we investigate the dynamics of a LipkinMeshkovGlick model under quasiperiodic kicking. Intriguingly, this infiniterangeinteracting spin chain can exhibit longlived periodic oscillations when the kicking amplitudes are drawn from the ThueMorse sequence (TMS). We dub this phase a ``selfordered time crystal" (SOTC), and demonstrate that our model hosts at least two qualitatively distinct prethermal SOTC phases. These SOTCs are robust to various perturbations, and they originate from the interplay of longrange interactions and the recursive structure of the TMS. Our results suggest that quasiperiodic driving protocols can provide a promising route for realizing novel nonequilibrium phases of matter in longrange interacting systems. 
Wednesday, March 16, 2022 5:12PM  5:24PM 
Q33.00010: Dissipative phase transition with drivingcontrolled spatial dimension and diffusive boundary conditions Zejian Li, Ferdinand Claude, Thomas Boulier, Elisabeth Giacobino, Quentin Glorieux, Alberto Bramati, Cristiano Ciuti We investigate theoretically and experimentally a firstorder dissipative phase transition, with diffusive boundary conditions and the ability to tune the spatial dimension of the system [1]. The considered physical system is a planar semiconductor microcavity in the strong lightmatter coupling regime, where polariton excitations are injected by a quasiresonant optical driving field. The spatial dimension of the system from 1D to 2D is tuned by designing the intensity profile of the driving field. We investigate the emergence of criticality by increasing the spatial size of the driven region. The system is nonlinear due to polaritonpolariton interactions and the boundary conditions are diffusive because the polaritons can freely diffuse out of the driven region. We show that no phase transition occurs using a 1D driving geometry, while for a 2D geometry we do observe both in theory and experiments the emergence of a firstorder phase transition. 
Wednesday, March 16, 2022 5:24PM  5:36PM 
Q33.00011: Optical Indistinguishability via Twinning Fields Gerard McCaul, Denys I Bondar Here we introduce the concept of the twinning field—a driving electromagnetic pulse that induces an identical optical response from two distinct materials. We show that for a large class of pairs of generic manybody systems, a twinning field which renders the systems optically indistinguishable exists. The conditions under which this field exists are derived, and this analysis is supplemented by numerical calculations of twinning fields for both the 1D FermiHubbard model, and tightbinding models of graphene and hexagonal boron nitride. The existence of twinning fields may lead to new research directions in nonlinear optics, materials science, and quantum technologies. 
Wednesday, March 16, 2022 5:36PM  5:48PM 
Q33.00012: Probing the thermodynamic limit of the photon blockade breakdown phase transition Riya Sett, Farid Hassani Bijarbooneh, Duc Phan, Shabir Barzanjeh, András Vukics, Johannes M Fink The photon blockade breakdown process (PBB) in the drivendissipative JaynesCummings model has been identified as an example for a first order quantum phase transition. In this work, we experimentally study the PBB using one superconducting transmon qubit coupled to a single resonator mode in the presence of a strong resonant drive. We back out the phase diagram and the characteristic switching time scales as a function of drive detuning and normalized coupling strength g/κ with g being the qubit  photon coupling strength and κ the insitu controlled cavity linewidth. For the smallest κ, we observe a mean switching timescale of up to 6 seconds, which is more than seven orders of magnitude longer than the characteristic lifetime of the system without the applied drive tone. This longtime stabilization of two macroscopic phases by a single qubit provides convincing evidence for the interpretation of the PBB as a first order quantum phase transition in a finitesize zerodimensional system with a welldefined thermodynamic limit. 
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