Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session J18: Exploring ErgodicityBreaking Through Nonequilibrium Order, Quantum Chaos and IntegrabilityInvited

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Sponsoring Units: DAMOP Chair: Bryce Gadway, University of Illinois at UrbanaChampaign Room: 205 
Tuesday, March 3, 2020 2:30PM  3:06PM 
J18.00001: Entanglement entropy of highly excited eigenstates of manybody lattice Hamiltonians Invited Speaker: Marcos Rigol The average entanglement entropy of subsystems of random pure states is (nearly) maximal [1]. In this talk, we discuss how the average entanglement entropy of subsystems of highly excited eigenstates of integrable and nonintegrable manybody lattice Hamiltonians (with a conservation law) differ from that of random pure states. For translationally invariant quadratic models (or spin models mappable to them) we prove that, when the subsystem size is not a vanishing fraction of the entire system, the average eigenstate entanglement exhibits a leading volumelaw term that is different from that of random pure states [2]. We argue that such a leading term is universal for translationally invariant quadratic models [3] and, likely, also for interacting integrable models [4]. For highly excited eigenstates of a particlenumberconserving quantum chaotic model away from half filling, we find that the deviation from the maximal value grows with the square root of the system's volume, when 1/2 of the system is traced out. Such a deviation is proved to occur in random pure states with a fixed particle number and normally distributed real coefficients [5]. 
Tuesday, March 3, 2020 3:06PM  3:42PM 
J18.00002: Universal operator growth and emergent hydrodynamics in quantum systems Invited Speaker: Ehud Altman I will present a hypothesis on universal properties of operators evolving under manybody Hamiltonian dynamics. I will define a measure of operator complexity and argue that it generically grows exponentially in time, with an exponent α, measurable through the properties of a physical retarded correlation function. Furthermore, the complexity exponent places a sharp bound on Lyapunov exponents λ ≤ 2α characterizing chaos, generalizing the known universal lowtemperature bound λ ≤ 2πT. In a sense the complexity growth exponent offers a measure of chaos that does not rely on having a nearby semiclassical limit. I will illustrate the results in paradigmatic examples such as nonintegrable quantum spin chains, the SachdevYeKitaev model, and classical models. Finally I will present applications of this approach to computation of Hydrodynamic transport coefficients and for characterizing the manybody localization transition in disordered systems. 
Tuesday, March 3, 2020 3:42PM  4:18PM 
J18.00003: Rydberg Mediated Interactions AtombyAtom and PhotonbyPhoton Invited Speaker: Vladan Vuletic Recent years have seen a remarkable development in our ability to manipulate individual atoms and individual photons, including the ability to design strong and controlled interactions. The interaction range between highly excited atomic states (Rydberg states) can substantially exceed an optical wavelength, which allows one to trap and manipulate individual atoms optically, yet induce controlled interactions on demand to implement quantum gates, create highly entangled states, or study quantum phase transitions. 
Tuesday, March 3, 2020 4:18PM  4:54PM 
J18.00004: Abstract Withdrawn

Tuesday, March 3, 2020 4:54PM  5:30PM 
J18.00005: Kinetically constrained dynamics and electronphonon interactions in Rydberg quantum simulators Invited Speaker: Igor Lesanovsky Rydberg quantum simulators, i.e. highly excited atoms held in optical tweezer arrays, are amongst the most advanced platforms for the implementation and study of strongly interacting spin systems. An interesting dynamical regime is reached when one atom that is brought to a Rydberg states facilitates the excitation of another nearby one. The resulting dynamics can be similar to that of epidemic spreading and also may form an ingredient for observing nonequilibrium phase transitions. In my talk I will discuss recent results concerning the analysis of constrained Rydberg spin dynamics in the presence of disorder which is caused by the coupling of electronic degrees of freedom and lattice vibrations. I will focus on incoherent and coherent regimes, discussing the breaking of ergodicity and the dressing of facilitated spins by phonons, respectively. 
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