Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session T45: KardarParisiZhang Universality in Quantum Many Body SystemsInvited Live Streamed

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Sponsoring Units: DCMP DAMOP Chair: Sarang Gopalakrishnan Room: McCormick Place W375D 
Thursday, March 17, 2022 11:30AM  12:06PM 
T45.00001: Detection of KardarParisiZhang hydrodynamics in a quantum Heisenberg spin chain Invited Speaker: David A Tennant Classical hydrodynamics is a remarkably versatile description of the coarsegrained behavior of manyparticle systems once local equilibrium has been established. The form of the hydrodynamical equations is determined primarily by the conserved quantities present in a system. Some quantum spin chains are known to possess, even in the simplest cases, a greatly expanded set of conservation laws, and recent work suggests that these laws strongly modify collective spin dynamics, even at high temperature. Here, by probing the dynamical exponent of the onedimensional Heisenberg antiferromagnet KCuF3 with neutron scattering, we find evidence that the spin dynamics are well described by the dynamical exponent z = 3/2, which is consistent with the recent theoretical conjecture that the dynamics of this quantum system are described by the Kardar–Parisi–Zhang universality class. This observation shows that lowenergy inelastic neutron scattering at moderate temperatures can reveal the details of emergent quantum fluid properties like those arising in nonFermi liquids in higher dimensions. 
Thursday, March 17, 2022 12:06PM  12:42PM 
T45.00002: Initial condition dependence of KPZ universality: from soft matter experiments to quantum spin chains Invited Speaker: Kazumasa A Takeuchi While the KardarParisiZhang (KPZ) universality class has been established as a prominent class for random growth processes and many other stochastic problems in nonequilibrium but classical physics, it is only recently that KPZ turned out to rule quantum spin chains of the isotropic Heisenberg model. This implies that a wealth of knowledge from classical KPZ systems may be utilized to unveil characteristic statistical properties of the fluctuating quantum spins. Particularly noteworthy is the fact that the KPZ class splits into a few "universality subclasses" depending on the initial condition [1], which may potentially contribute to characterize thermalization of such quantum spins. 
Thursday, March 17, 2022 12:42PM  1:18PM 
T45.00003: KardarParisiZhang universality from soft modes in spin chains Invited Speaker: Vir B Bulchandani

Thursday, March 17, 2022 1:18PM  1:54PM 
T45.00004: Superuniversality of superdifusion in integrable manybody systems with nonabelian symmetries Invited Speaker: Tomasz Prosen I will present a plethora of computational evidence for superuniversality of superdiffusive spin (or, generally, Noether charge) transport in integrable spin chains with arbitrary nonabelian symmetries. The most prominent example is the quantum Heisenberg magnet, while other quantum and classical integrable chains with nonabelian Lie group symmetries are shown to yield identical phenomenology. The twopoint functions (e.g. dynamical spin structure factor) at high temperature are shown to be described by KardarParisiZhang (KPZ) universality class with dynamical exponent z=3/2. This is remarkable, as KPZ universality in stochastic growth and related processes applies to manifesly nonequilibrium situations, while in the present context of equilibrium spin transport we show that KPZ universality breaks down to diffusive universality when introducing nonequilibrium initial states with a finite magnetization bias which break the nonabelian symmetry. The talk will be concluded by the discussion of the most pressing open theoretical questions. 
Thursday, March 17, 2022 1:54PM  2:30PM 
T45.00005: Observation of KardarParisiZhang superdiffusion in a Heisenberg quantum magnet Invited Speaker: David Wei The KardarParisiZhang universality class describes the coarsegrained dynamics of numerous classical stochastic models. Surprisingly, it was recently conjectured, that spin transport in the onedimensional (1D) quantum Heisenberg model falls into this class. In our experiment, we employ a coldatom quantum simulator to verify this conjecture by studying the hydrodynamic relaxation of spindomain walls. We find that transport is superdiffusive and indeed obeys the characteristic KPZ spacetime scaling with dynamical exponent z=3/2. We observe that superdiffusion breaks down when probing dynamics both in the 2D model and in the netmagnetized 1D model, which supports the notion that integrability and the nonabelian SU(2) symmetry of the 1D Heisenberg model give rise to its KPZ dynamics. Finally, we leverage the singlespinsensitive detection enabled by our quantumgas microscope to measure spintransport statistics, which yields a clear signature of the nonlinearity that is a hallmark of KPZ universality. 
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