Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session H27: Quantum Information in Relativistic and Condensed Matter SystemsFocus

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Sponsoring Units: DQI Chair: Shenglong Xu, University of Maryland, College Park Room: BCEC 160C 
Tuesday, March 5, 2019 2:30PM  2:42PM 
H27.00001: Quantum Interferometry Meets General Relativity Igor Pikovski The interplay between Einstein’s theory of gravity and quantum mechanics remains one of the open questions in physics. Each of the theories has been confirmed individually, but phenomena described by the two usually take place at very different physical regimes. Nevertheless, gravity can affect quantum systems and some aspects of the interplay can be probed in experiments. In this talk, I will discuss a quantum version of the "twin paradox" in which a clock is brought in superposition of being at two different gravitational potentials. The effect leads to new and measurable consequences at the interplay between quantum theory and general relativity and causes decoherence of composite quantum systems. I will also discuss how these effects can be accessed in quantum interference experiments. 
Tuesday, March 5, 2019 2:42PM  2:54PM 
H27.00002: Gravitational entanglement with Gaussian states Sofia Qvarfort, Sougato Bose, Alessio Serafini Is gravity a quantum force? This question was recently addressed by two proposals (see [1] and [2]) which explored the possibility of detecting entanglement as generated by gravity. Successful detection of entanglement due to a gravitational interaction would imply that gravity is fundamentally a quantum force, since only quantum systems can mediate entanglement. 
Tuesday, March 5, 2019 2:54PM  3:06PM 
H27.00003: General relativistic time dilation and spacetime uncertainty in quantum clocks Shishir Khandelwal, Maximilian P. E. Lock, Mischa Woods The general theory of relativity associates a proper time with each object via its spacetime trajectory. In quantum theory on the other hand, such trajectories are forbidden. Here we demonstrate that, in the weakfield and lowvelocity limit, all “good” quantum clocks experience the time dilation dictated by general relativity for the most classical states of motion. For nonclassical states of motion, on the other hand, we find that quantum interference effects give rise to a significant discrepancy between the proper time and the time measured by the clock. Moreover, we show how our ignorance of the clock’s state of motion leads to a larger uncertainty in time measurements with the clock, a consequence of entanglement between the clock time and its centerofmass degrees of freedom. 
Tuesday, March 5, 2019 3:06PM  3:42PM 
H27.00004: Ontological models for relativistic quantum information Invited Speaker: Ian Durham Epistemic models of nature prove to be problematic in many settings, particularly in those for which measurement procedures are illdefined. By contrast, in ontic models of nature, measurement results are independent of the procedure used to obtain them. If we assume that all measurement results can be expressed in terms of pointer readings, then any useful ontology would need to unambiguously specify the positions of things. We review a number of proposals for such ontologies in the context of relativistic quantum information and quantum manybody theories, and we propose a new ontology based on the WheelerDeWitt equation that overcomes some of the problems inherent in existing models. Our model includes a set of deterministic constraints for the geometry, matter field, and action. 
Tuesday, March 5, 2019 3:42PM  3:54PM 
H27.00005: Relativistic wave equations from quantum walks Todd Brun, Leonard Mlodinow Quantum walks are unitary analogues of classical random walks. We examine the quantum walk on the 3D bodycentered lattice, and show that a set of natural symmetry assumptions lead, in the long wavelength limit, to its wave functions becoming solutions to the Dirac equation. These assumptions require at least a fourdimensional internal space. Taking this as a model of a particle propagating in discrete spacetime, we show that the discreteness could be detected in nonparallel matter interferometers. We also look at the problem of generalizing to the manybody case, by replacing the quantum walk with a quantum cellular automaton that gives the same evolution as the quantum walk for the singleparticle sector. This automaton approaches a quantum field theory in the longwavelength limit. 
Tuesday, March 5, 2019 3:54PM  4:06PM 
H27.00006: LiebRobinsonType Bounds for Quantum Systems with Strongly LongRange Interactions Andrew Guo, Cong Minh Tran, Andrew Childs, Alexey V Gorshkov, ZheXuan Gong We prove bounds on the rate of correlationspreading in longrange quantum lattice systemsspecifically those with interaction strengths that decay as a powerlaw r^{α} in the distance r. Such longrange interacting systems include dipolar spin interactions in neutral atoms and molecules, as well as tunable spinspin interactions in trapped ions. For strongly longrange Hamiltonians with α less than the lattice dimension, we give two new LiebRobinsontype bounds. First, we prove a tight bound on freeparticle Hamiltonians with longrange hopping terms and provide a protocol for quantum state transfer that saturates the bound. We also prove a general bound for interacting Hamiltonians that gives the smallest causal region compared to existing general bounds. This latter result gives a lower bound on the fastest possible scrambling time for a longrange interacting system. 
Tuesday, March 5, 2019 4:06PM  4:18PM 
H27.00007: Locality and digital quantum simulation of powerlaw interactions Minh Tran, Andrew Y Guo, Yuan Su, James Garrison, Zachary Eldredge, Michael FossFeig, Andrew Childs, Alexey V Gorshkov The propagation of information in nonrelativistic quantum systems obeys a speed limit known as a LiebRobinson bound. We derive a new LiebRobinson bound for systems with interactions that decay with distance r as a power law, 1/r^{α}. The bound implies an effective light cone tighter than all previous bounds. Our approach is based on a technique for approximating the time evolution of a system, which was first introduced as part of a quantum simulation algorithm by Haah et al. [arXiv:1801.03922]. To bound the error of the approximation, we use a known LiebRobinson bound that is weaker than the bound we establish. This result brings the analysis full circle, suggesting a deep connection between LiebRobinson bounds and digital quantum simulation. In addition to the new LiebRobinson bound, our analysis also gives an error bound for the Haah et al. quantum simulation algorithm when used to simulate powerlaw decaying interactions. In particular, we show that the gate count of the algorithm scales with the system size better than existing algorithms when α>3D (where D is the number of dimensions). 
Tuesday, March 5, 2019 4:18PM  4:54PM 
H27.00008: Composite quantum systems at the interface with general relativity Invited Speaker: Magdalena Zych A major goal of modern physics is to understand and test the regime where quantum mechanics and general relativity both play a role. However, new effects of this regime are usually thought to be relevant only at high energies or in strong gravitational fields, beyond the reach of presentday experiments. I will discuss a novel framework for achieving this goal, focused on lowenergy but composite quantum systems and using the tools of quantum information science. Quantum coherence of composite particles can be measurably affected by general relativity even at lowenergies and in weak gravitational fields through time dilation. I will explain the resulting new phenomena and how they can be tested. I will discuss broader relevance of the approach for quantum sensing, communication and quantum information processing. 
Tuesday, March 5, 2019 4:54PM  5:06PM 
H27.00009: Signature of quantum chaos in operator entanglement in 2d conformal field theories Laimei Nie, Masahiro Nozaki, Shinsei Ryu, Mao Tian Tan We study operator entanglement measures of the unitary evolution operators of (1+1)dimensional conformal field theories (CFT), aiming to uncover their scrambling and chaotic behaviors. In particular, we compute the bipartite and tripartite mutual information for various configurations of input and output subsystems, and as a function of time. We contrast three different CFTs: the free fermion, the compactified free boson at various radii, and CFTs with holographic dual. We found that the bipartite mutual information exhibits distinct behaviors for these CFTs, reflecting the different information scrambling capabilities of these unitary operators; while a quasiparticle picture can describe well the case the free fermion and free boson CFTs, it completely fails for the case of holographic CFTs. Similarly, the tripartite mutual information also distinguishes the unitary evolution operators of different CFTs. In particular, its late time behaviors, when the output subsystems are semiinfinite, are quite distinct for these theories. We speculate that for holographic theories the late time value of the tripartite mutual information saturates the lower bound among quantum field theories. 
Tuesday, March 5, 2019 5:06PM  5:18PM 
H27.00010: Exact bosonization in two and three spatial dimensions and new classes of lattice gauge theory YuAn Chen, Anton Kapustin, Djordje Radicevic We will describe 2d (3d) analogs of the JordanWigner transformation which maps an arbitrary fermionic system on a 2d (3d) lattice to a lattice gauge theory while preserving the locality of the Hamiltonian. The lattice gauge theory can be understood us a stabilizer code. When the space is simplyconnected, this bosonization map is an equivalence. On 2d square lattice, our bosonization mapping is equivalent to BravyiKitaev "Superfast simulation of Fermions" and it has possible applications on quantum simulation of fermions. We also describe Euclidean actions for the corresponding lattice gauge theories and find that the (2+1)D theory contains ChernSimonslike terms, which can be considered as Z/2Z version of particlevortex duality. 
Tuesday, March 5, 2019 5:18PM  5:30PM 
H27.00011: Momentumspace entanglement of disordered noninteracting onedimensional fermions after a quantum quench Rex Lundgren, Fangli Liu, Pontus Laurell, Gregory Fiete We investigate the momentumspace entanglement entropy and spectrum of several disordered onedimensional freefermion systems that circumvent Anderson localization, such as the randomdimer model, after a quantum quench. We numerically observe two different types of momentumspace entanglement entropy dynamics, an interesting slow logarithmiclike growth followed by saturation or rapid saturation. The type of dynamics one observes depends on the Fermi level of the intial state and the scattering matrix element structure in momentumspace. We then discuss when the momentumspace entanglement spectrum reveals the presence of delocalized states after a quench in these systems. We find if there are vanishing momentumscattering states, the momentumspace entanglement spectrum clearly reveals the presence of delocalized states for long times. 
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