Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session K34: NonEquilibrium Physics with Cold Atoms and Molecules, Rydberg Gases, and Trapped Ions IFocus Recordings Available

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Sponsoring Units: DAMOP DCMP Chair: Oliver Hart, University of Colorado, Boulder Room: McCormick Place W193A 
Tuesday, March 15, 2022 3:00PM  3:12PM 
K34.00001: Controlling thermoelectric transport and dissipation effects in superfluid transport in an atomic transport experiment Philipp Fabritius We report on the control of the thermoelectric transport properties of a strongly interacting Fermi gas flowing through a quasitwodimensional contact and the effects of dissipation on nonlinear superfluid transport through a quantum point contact (QPC). The versatility of coldatom techniques allows us to precisely define a QPC using light potentials, to directly measure particle, heat and spin currents and to tune interatomic interactions. In a first experiment, we probe the thermoelectric effects induced by a temperature difference across a twodimensional channel. We use an attractive as well as a repulsive gate to change the relative strength of channel and reservoir contributions to the thermoelectric transport. This allows us to tune the particle transport going from hot to cold to going from cold to hot. We find that strong interactions reduce the Seebeck coefficient of the channel which we attribute to hydrodynamic effects and resulting superfluid correlations inside the channel. In a second experiment, we locally dissipate a single spin state inside the QPC using an optical tweezer. We find that the dissipation has a strong effect on the nonlinear transport behavior of the superfluid transport making it linear. We also report on Keldysh theory calculations of the superfluid transport behavior with dissipation and compare them with our experimental results. These results open the way to the quantum simulation of the coupling between spin, heat and particle currents with cold atoms. 
Tuesday, March 15, 2022 3:12PM  3:24PM 
K34.00002: Boosting the Quantum State of a Cavity with Floquet Driving David M Long, Philip Crowley, Alicia Kollar, Anushya Chandran The striking nonlinear effects exhibited by cavity QED systems make them a powerful tool in modern condensed matter and atomic physics. A recently discovered example is the topologically quantized pumping of energy into a cavity by a stronglycoupled, periodicallydriven spin. We uncover a remarkable feature of these energy pumps: they coherently translate, or boost, a quantum state of the cavity in the Fock basis. Boosting enables the preparation of highlyexcited nonclassical cavity states in nearterm optical cavity and circuit QED experiments. 
Tuesday, March 15, 2022 3:24PM  3:36PM 
K34.00003: Hidden quasiconservation laws in fracton hydrodynamics Oliver Hart, Andrew Lucas, Rahul Nandkishore We show that the simplest universality classes of fracton hydrodynamics, including isotropic theories of charge and dipole conservation, can exhibit hidden "quasiconservation laws", in which certain higher multipole moments can only decay due to dangerously irrelevant corrections to hydrodynamics. We present two simple examples of this phenomenon. Firstly, an isotropic dipoleconserving fluid in the infinite plane conserves an infinite number of "harmonic multipole charges" within linear response; we calculate the decay/growth of these charges due to dangerously irrelevant nonlinearities. Secondly, we consider a model with xy and x^{2}y^{2} quadrupole conservation, in addition to dipole conservation, which is described by isotropic fourthorder subdiffusion, yet has dangerously irrelevant sixthorder corrections necessary to relax the harmonic multipole charges. We confirm our predictions for the anomalously slow decay of the harmonic conserved charges in each setting by using numerical simulations, both of the nonlinear hydrodynamic differential equations, and in quantum automaton circuits on a square lattice. 
Tuesday, March 15, 2022 3:36PM  4:12PM 
K34.00004: An optical lattice with sound Invited Speaker: Benjamin L Lev Quantised sound waves—phonons—govern the elastic response of crystalline materials, and also play an integral part in determining their thermodynamic properties and electrical response (e.g., by binding electrons into superconducting Cooper pairs). 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 stiff. Opticallattice realisations of crystals therefore lack some of the central dynamical degrees of freedom that determine the lowtemperature properties of real materials. Here, we create an optical lattice with phonon modes using a BoseEinstein condensate (BEC) coupled to a confocal optical resonator—a vibrating supersolid. Playing the role of an active quantum gas microscope, the multimode cavity QED system both images the phonons and induces the crystallisation that supports phonons via short range, photonmediated atomatom interactions. Dynamical susceptibility measurements reveal the phonon dispersion relation, showing that these collective excitations exhibit a sound speed dependent on the BECphoton coupling strength. Our results pave the way for exploring the rich physics of elasticity in quantum solids. 
Tuesday, March 15, 2022 4:12PM  4:24PM 
K34.00005: Simulations of Bose Dynamics at Finite Temperature by Complex Langevin Sampling Coherent States on a Keldysh Contour Kris T Delaney, Henri Orland, Glenn H Fredrickson Efficient and scalable methods for simulating the exact dynamical evolution of finitetemperature, interacting Bosons subject to a timedependent external potential are very challenging to develop. We previously reported a stable and efficient algorithm based on complex Langevin dynamics for sampling the equilibrium coherent states field theory of an assembly of interacting bosons, and we demonstrated its correctness by locating the BoseEinstein condensation transition temperature in a φ^{4} theory of contact interactions. In this talk, we detail an extension of this algorithm to permit sampling configurations on a Keldysh contour. The new algorithm permits evaluation of the realtime causal Green function and all dependent dynamical properties without approximations. 
Tuesday, March 15, 2022 4:24PM  4:36PM 
K34.00006: Dissipative Floquet Dynamics: from Steady State to Measurement Induced Criticality in Trappedion Chains Guido Pagano, Piotr Sierant, Giuliano Chiriaco, Federica Maria Surace, Xhek Turkeshi, Shradda Sharma, Marcello Dalmonte, Rosario Fazio Quantum systems evolving unitarily and subject to quantum measurements exhibit various types 
Tuesday, March 15, 2022 4:36PM  4:48PM 
K34.00007: Edge dynamics of the Ising chain in the presence of a static boundary field umar javed, Michael Kolodrubetz, Jamir Marino, Vadim Oganesyan We study dynamics of the onedimensional Ising model in the presence of static boundary field (h_{B}) via the twotime correlation function of the boundary spin, │〈σ^{z}_{1 }(0)σ^{z}_{1 }(t)〉_{c }│. We find that the correlations decay as a power law. Interestingly, we unveil a dynamical phase diagram, previously uncharted, where upon tuning the strength of the boundary field and distance from bulk critical point, we observe qualitatively distinct temporal behavior in correspondence to the change of number of edge modes as h_{B} and the bulk transverse field vary. These dynamical boundary phase transitions are separated by critical lines. In the presence of large boundary and bulk field, correlations are infinitely long lived and can be trace back to stability of nonzero energy fermionic edge mode and a zero energy Majorana edge mode, yielding a stable qubit. We suggest how the universal physics can be demonstrated in Rydberg chains. 
Tuesday, March 15, 2022 4:48PM  5:00PM 
K34.00008: Eigenstate prethermalization Nicholas O'Dea, Fiona J Burnell, Anushya Chandran, Vedika Khemani Experimental advances in periodic driving fields allow for the manipulation of quantum phases of matter and the design of Floquetengineered effective Hamiltonians. The driving, which breaks time translation invariance, ultimately thermalizes the system to a featureless infinite temperature state. Nevertheless, there are rigorous exponentialinfrequency bounds on the heating rates, allowing for nontrivial dynamics for long periods of time. While these bounds apply for global quasiconservation laws such as energy, we show that even individual manybody eigenstates of a leading order effective Hamiltonian, $H_0$, show longlived fidelity under the time evolution generated by the full, driven Hamiltonian. Our results have promising implications for Floquet engineering, and are especially interesting when $H_0$ has outlier eigenstates, called scar states. 
Tuesday, March 15, 2022 5:00PM  5:12PM 
K34.00009: Towards nonequilibrium spin dynamics with spin spirals in dense ensembles of NV centers Oksana A Makarova, Leigh S Martin, Christina Spaegele, Hengyun Zhou, Nathaniel T Leitao, QianZe Zhu, Bartholomeus Machielse, Johannes Cremer, Nishad Maskara, Hongkun Park, Ronald L Walsworth, Federico Capasso, Mikhail Lukin Exploring farfromequilibrium systems is an exciting frontier of manybody physics. We present the construction of a new setup to probe manybody dynamics and spin diffusion in longrange interacting spin systems, combining Hamiltonian engineering with spatial control on the scale of the typical NVNV spacing. We achieve the latter by applying strong magnetic field gradients that can be rapidly switched during the Hamiltonian engineering pulse sequence. In addition to altering the Hamiltonian during the engineering phase, gradients can also prepare nontrivial spin spiral initial states. We estimate that magnetic field gradients on the order of 0.11 G/nm are achievable, enabling spin spirals with windings on the order of the spin spacing. Our new experimental apparatus will allow us to study manybody thermalization and the emergence of hydrodynamics in complex manybody quantum systems. 
Tuesday, March 15, 2022 5:12PM  5:24PM 
K34.00010: Taking the temperature of a pure quantum state Mark T Mitchison, Archak Purkayastha, Marlon Brenes, Alessandro Silva, John Goold Temperature is a deceptively simple concept that still raises deep questions at the forefront of quantum physics research. The observation of thermalisation in completely isolated quantum systems, such as coldatom quantum simulators, implies that a temperature can be assigned even to individual, pure quantum states. Here, we propose a scheme to measure the temperature of such pure states through quantum interference. Our proposal involves interferometry of an auxiliary qubit probe, which is prepared in a superposition state and subsequently undergoes decoherence due to weak coupling with a closed, thermalised manybody system. Using only a few basic assumptions about chaotic quantum systems — namely, the eigenstate thermalisation hypothesis and the emergence of hydrodynamics at long times — we show that the qubit undergoes pure exponential decoherence at a rate that depends on the temperature of its surroundings. We verify our predictions by numerical experiments on a quantum spin chain that thermalises after absorbing energy from a periodic drive. Our work provides a general method to measure the temperature of isolated, strongly interacting systems under minimal assumptions. 
Tuesday, March 15, 2022 5:24PM  5:36PM 
K34.00011: A tracer diffusion interpretation of anomalous transport in constrained quantum matter Johannes Feldmeier, William WitczakKrempa, Michael Knap In recent works a zoo of constrained quantum manybody systems with anomalous transport properties has been identified. A crucial challenge now is to distill potential underlying unifying principles giving rise to such anomalous transport. Here, we will show that for various constrained quantum systems the concept of tracer diffusion, that is diffusion of tagged particles with infiniterepulsive interactions, provides intriguing insights into their anomalous transport properties. A central ingredient for our interpretation is to identify conserved charge patterns in constrained quantum systems through an appropriate change of variables. We will apply this concept both to nonintegrable random unitary circuit models as well as to integrable systems, including the tJz Hamiltonian in the weak Jz limit and the folded Heisenberg model (the Heisenberg model with infinitely strong easyaxis anisotropy). For these systems, tracer diffusion even allows us to calculate the exact values and the parameter dependence of microscopic diffusion constants. 
Tuesday, March 15, 2022 5:36PM  5:48PM 
K34.00012: Completing the Floquet picture: the missing quantum number Cristian M Le, Akashi Ryosuke, Shinji Tsuneyuki The Floquet method in quantum mechanics has become a central tool for calculating periodically driven quantum systems; however, there are known limitations to this method that limit its applicability. The primary issues are the lack of a bounded ordering of the eigenstates and the infinite quasienergy degeneracy in the continuum, which rule out a Ritz variation principle and efficient firstprinciples computation methods based on it. Moreover, the Floquet states are considered to be the energytime counterparts of the spatially periodic Bloch states; however, if we properly follow this analogy, we find that there is no equivalent energy quantum number in the current Floquet formalism based on the quasienergy. 
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