Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session V34: Precision Many Body Physics VFocus

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Sponsoring Units: DCOMP DAMOP DCMP Chair: Adrian Del Maestro, Univ of Vermont Room: LACC 409A 
Thursday, March 8, 2018 2:30PM  3:06PM 
V34.00001: Floquet Supersymmetry Invited Speaker: Thomas Iadecola We introduce the notion of timereflection symmetry in periodically driven (Floquet) quantum systems, and show that it enables a Floquet variant of quantummechanical supersymmetry. In particular, we find Floquet analogues of the Witten index that place lower bounds on the degeneracies of states with quasienergies 0 and π. We provide a simple class of disordered, interacting, and ergodic Floquet models with an exponentially large number of states at quasienergies 0,π, which are robust as long as the timereflection symmetry is preserved. Floquet supersymmetry manifests itself in the evolution of certain local observables as a perioddoubling effect with dramatic finitesize scaling, providing a clear signature for experiments. 
Thursday, March 8, 2018 3:06PM  3:18PM 
V34.00002: Spin transport of weakly disordered Heisenberg chain at infinite temperature Ilia Khait, Snir Gazit, Norman Yao, Assa Auerbach We study the disordered Heisenberg spin chain, which exhibits many body localization at strong disorder, in the weak to moderate disorder regime. A continued fraction calculation of dynamical correlations is devised, using a variational extrapolation of recurrents. Good convergence for the infinite chain limit is shown. We find that the local spin correlations decay at long times as C ∼ t^{β}, while the conductivity exhibits a low frequency power law σ ∼ ω^{α}. The exponents depict subdiffusive behavior β<1/2, α>0 at all finite disorders, and convergence to the scaling result, α+2β=1, at large disorders. 
Thursday, March 8, 2018 3:18PM  3:30PM 
V34.00003: Time crystals in doped semiconductors Arijeet Pal, James O'Sullivan, Michael Thewalt, John Morton Spin ensembles in semiconductors provide a unique experimental platform for the observation of emergent manybody dynamics like manybody localization and quantum chaos. High precision quantum control of electron and nuclear spins in phosphorus doped silicon have been utilized to uncover the manybody correlations in decoherence. We present here the experimental observation of a manybody time crystal, a novel dynamical phase of matter with spontaneously broken time translation symmetry, in periodically driven nanoscale electron spins in phosphorus doped silicon. The signatures of time crystalline correlations were studied as a function of spin concentration. These observations can be theoretically captured by the paradigmatic central spin model previously used for describing decoherence in this system. 
Thursday, March 8, 2018 3:30PM  3:42PM 
V34.00004: Quantum quenches and relaxation dynamics in the thermodynamic limit Krishnanand Mallayya, Marcos Rigol We implement numerical linked cluster expansion (NLCEs) to study dynamics of onedimensional systems of hardcore bosons close to an integrable point in the thermodynamic limit. We find that local observables exhibit exponential relaxation in the time scales accessible to us. We calculate the relaxation rates and find that they scale quadratically with the strength of the integrability breaking perturbation. 
Thursday, March 8, 2018 3:42PM  3:54PM 
V34.00005: NonEquilibrium Transport in the Quantum Dot: Quench Dynamics and NonEquilibrium Steady State Adrian Culver, Natan Andrei We present an exact method of calculating the nonequilibrium current driven by a voltage drop across a quantum dot. The system is described by the two lead Kondo model with noninteracting Fermiliquid leads at zero temperature. We prepare the system in an initial state consisting of a free Fermi sea in each lead with the voltage drop given as the difference between the two Fermi levels. We quench the system by coupling the dot to the leads at $t=0$ and following the time evolution of the wavefunction. In the long time limit a steady state emerges provided that the size of the system is large compared to the time of evolution (open system limit). A new type of Bethe Ansatz wavefunction describes the system  it satisfies the LippmannSchwinger equation with the two Fermi seas serving as the boundary conditions. We present this wavefunction and give an infinite series expression for the current evaluated in this state to obtain the nonequilibrium steady state current as a function of the voltage. Evaluation of this series is discussed. 
Thursday, March 8, 2018 3:54PM  4:06PM 
V34.00006: Onedimensional Bose gas dynamics: breather fragmentation and quantum correlations Peter Drummond, Bogdan Opanchuk, King Ng Both exact conservation laws and dynamical invariants exist in the topical case of the onedimensional ultracold atomic Bose gas, providing a validation of methods for precision quantum dynamics. The first four quantum conservation laws are exactly conserved in the approximate truncated Wigner approach to manybody quantum dynamics, which is a 1/N expansion for N atoms. Centerofmass position variance is exactly calculable, and is nearly exact in the truncated Wigner approximation, apart from small terms that vanish as N^{3/2} as N→∞. 
Thursday, March 8, 2018 4:06PM  4:18PM 
V34.00007: Quantum spin chains with multiple dynamics Xiao Chen, Eduardo Fradkin, William WitczakKrempa Manybody systems with multiple emergent time scales arise in various contexts, including correlated quantum materials and ultracold atoms. We investigate such nontrivial quantum dynamics in a new setting: a spin1 bilinearbiquadratic chain. It has a solvable entangled groundstate, but a gapless excitation spectrum that is poorly understood. By using largescale DMRG simulations, we find that the lowest excitation has a dynamical exponent z that varies from 2 to 3.2 as we vary a coupling in the Hamiltonian. We find an additional gapless mode with a continuously varying exponent, which establishes the presence of multiple dynamics. In order to explain these striking properties, we construct a field theory and determine various correlation functions and entanglement properties, as well as an exact mapping to the nonequilibrium dynamics of a classical spin chain. Finally, we discuss the connections to other spin chains and to a family of quantum critical models in 2d. 
Thursday, March 8, 2018 4:18PM  4:30PM 
V34.00008: Incomplete thermalization from trapinduced integrability breaking: lessons from classical hard rods Xiangyu Cao, Vir Bulchandani, Joel Moore The familiar Newton’s cradle can be modeled as a onedimensional gas of hard rods trapped in a harmonic potential, which breaks integrability of the hardrod interaction in a nonuniform way. We explore the consequences of such broken integrability for the dynamics of a large number of particles and find three distinct regimes: initial, chaotic, and stationary. The initial regime is captured by an evolution equation for the phasespace distribution function. However, for any finite number of particles, this hydrodynamics breaks down due to a “complexity crisis” and the dynamics become chaotic after a characteristic time scale determined by the interparticle distance and scattering length. At long times, the system fails to thermalize and the timeaveraged ensemble of individual trajectories is not microcanonical, but it is a stationary state of the hydrodynamic evolution. We close by discussing logical extensions of the results to similar systems of quantum particles. 
Thursday, March 8, 2018 4:30PM  4:42PM 
V34.00009: Behaviour of lbits Near the ManyBody Localization Transition Abishek Kulshreshtha, Arijeet Pal, Thorsten Wahl, Steven Simon Eigenstates of fully manybody localized (FMBL) systems are described by quasilocal operators τ_{i}^{z} (lbits), which are conserved exactly under Hamiltonian time evolution. The algebra of the operators τ_{i}^{z} and τ_{i}^{x} associated with lbits τ_{i} completely define the eigenstates and the matrix elements of local operators between eigenstates at all energies. We develop a nonperturbative construction of the full set of lbit algebras in the manybody localized phase for the canonical model of MBL. Our algorithm to construct the Paulialgebra of lbits combines exact diagonalization and a tensor network algorithm developed for efficient diagonalization of large FMBL Hamiltonians. The distribution of localization lengths of the lbits is evaluated in the MBL phase and used to characterize the MBLtothermal transition. 
Thursday, March 8, 2018 4:42PM  4:54PM 
V34.00010: Singleparticle mobility edges in a onedimensional bichromatic incommensurate potential Xiao Li In this talk I will focus on a 1D mutually incommensurate bichromatic lattice system which has been implemented in ultracold atoms to study quantum localization. It has been universally believed that the tightbinding version of this bichromatic incommensurate system is represented by the wellknown AubryAndre (AA) model. Here we establish that this belief is incorrect and that the AA model description generically breaks down near the localization transition due to the unavoidable appearance of singleparticle mobility edges (SPME). As a result, for the full lattice system, an intermediate phase between completely localized and completely delocalized regions appears due to the existence of the SPME, making the system qualitatively distinct from the AA prediction. Our theoretical prediction is subsequently verified in an experiment using a onedimensional quasiperiodic optical lattice. In particular, a regime is identified where extended and localized singleparticle states coexist, in good agreement with our theoretical results. Our work thus presents the first realization of a system with an SPME in one dimension, and it opens up more research prospects in the context of manybody localization, including the question of manybody mobility edges. 
Thursday, March 8, 2018 4:54PM  5:06PM 
V34.00011: Manybody localization in spin chain systems with quasiperiodic fields Mac Lee, Thomas Look, SayPeng Lim, Donna Sheng We study the manybody localization of spin chain systems with quasiperiodic fields. We identify the lower bound for the critical disorder necessary to drive the transition between the thermal and manybody localized phase to be Wc>1.85, based on finitesize scaling of entanglement entropy and fluctuations of the bipartite magnetization. We also examine the time evolution of the entanglement entropy of an initial product state where we find powerlaw and logarithmic growth for the thermal and manybody localized phases, respectively, with a transition point Wc∼2.5. For larger disorder strength, both imbalance and spinglass order are preserved at long times, while spinglass order shows dependence on system size. We also explore density matrix renormalization group studies and explore a twolegged ladder model. Quasiperiodic fields have been applied in different experimental systems, and our study finds that such fields are very efficient at driving the manybody localized phase transition. 
Thursday, March 8, 2018 5:06PM  5:18PM 
V34.00012: Development of time dependent DMRG method for higher dimensional systems and its application to quantum annealing Shigetoshi Sota, Tomonori Shirakawa, Seiji Yunoki, Takami Tohyama In order to investigate quantum dynamics on higher dimensional strongly correlated systems, we have developed new kind of the time dependent DMRG (tDMRG) method using the kernel polynomial method (KPM). In our tDMRG method, a time depending state is directly calculated by the KPM. By a threeterm recursive formula of special functions, we can perform effective tDMRG calculations. Also, our tDMRG calculations give accurate results as long as we employ large enough DMRG truncation number. In the present study, we have applied our tDMRG method to quantum annealing which is a kind of quantum computing for optimization problems. In the quantum annealing, the Hamiltonian is constructed by a twodimensional Ising model with transverse magnetic field. Our tDMRG calculations of the quantum annealing give correct answer of optimization problems by using relatively small DMRG truncation number. Thus, our tDMRG method is suitable for numerical studies of the quantum annealing. 
Thursday, March 8, 2018 5:18PM  5:30PM 
V34.00013: Spectral Functions of the BilinearBiquadratic Spin1 Chain Moritz Binder, Thomas Barthel The bilinearbiquadratic spin1 chain exhibits a rich phase diagram. Depending on the two coupling strengths, the system can be in a ferromagnetic phase, a gapped dimer phase, the gapped Haldane phase with hidden topological longrange order, or an extended critical phase with periodthree structure and dominant quadrupolar correlations. Here, we use density matrix renormalization group (DMRG) algorithms to compute precise static structure factors and spectral functions in the different phases. We relate our results to insights from exact solutions at special points in the phase diagram and fieldtheoretical approaches. 
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