In quantum many-body systems with local interactions, quantum information and entanglement cannot spread outside of a "linear light cone," which expands at an emergent velocity analogous to the speed of light. Yet most non-relativistic physical systems realized in nature have long-range interactions: two degrees of freedom separated by a distance r interact with potential energy V(r)∝1/rα. In systems with long-range interactions, we rigorously establish a hierarchy of linear light cones: at the same α, some quantum information processing tasks are constrained by a linear light cone while others are not. In one spatial dimension, commutators of local operators ⟨ψ|[Ox(t),Oy]|ψ⟩ are negligible in every state |ψ⟩ when |x−y|≳vt, where v is finite when α>3 (Lieb-Robinson light cone); in a typical state |ψ⟩ drawn from the infinite temperature ensemble, v is finite when α>52 (Frobenius light cone); in non-interacting systems, v is finite in every state when α>2 (free light cone). These bounds apply to time-dependent systems and are optimal up to subalgebraic improvements. Our theorems regarding the Lieb-Robinson and free light cones, and their tightness, also generalize to arbitrary dimensions. We discuss the implications of our bounds on the growth of connected correlators and of topological order, the clustering of correlations in gapped systems, and the digital simulation of systems with long-range interactions. In addition, we show that quantum state transfer and many-body quantum chaos are bounded by the Frobenius light cone, and therefore are poorly constrained by all Lieb-Robinson bounds.

%B Physical Review X %V 10 %8 5/29/2020 %G eng %U https://arxiv.org/abs/2001.11509 %N 031009 %R https://doi.org/10.1103/PhysRevX.10.031009 %0 Journal Article %J Physical Review A %D 2020 %T Signaling and Scrambling with Strongly Long-Range Interactions %A Andrew Y. Guo %A Minh C. Tran %A Andrew M. Childs %A Alexey V. Gorshkov %A Zhe-Xuan Gong %XStrongly long-range interacting quantum systems---those with interactions decaying as a power-law 1/rα in the distance r on a D-dimensional lattice for α≤D---have received significant interest in recent years. They are present in leading experimental platforms for quantum computation and simulation, as well as in theoretical models of quantum information scrambling and fast entanglement creation. Since no notion of locality is expected in such systems, a general understanding of their dynamics is lacking. As a first step towards rectifying this problem, we prove two new Lieb-Robinson-type bounds that constrain the time for signaling and scrambling in strongly long-range interacting systems, for which no tight bounds were previously known. Our first bound applies to systems mappable to free-particle Hamiltonians with long-range hopping, and is saturable for α≤D/2. Our second bound pertains to generic long-range interacting spin Hamiltonians, and leads to a tight lower bound for the signaling time to extensive subsets of the system for all α<D. This result also lower-bounds the scrambling time, and suggests a path towards achieving a tight scrambling bound that can prove the long-standing fast scrambling conjecture.

%B Physical Review A %V 102 %8 7/8/2020 %G eng %U https://arxiv.org/abs/1906.02662 %N 010401(R) %R https://journals.aps.org/pra/abstract/10.1103/PhysRevA.102.010401 %0 Journal Article %J Phys. Rev. Lett. %D 2019 %T Probing ground-state phase transitions through quench dynamics %A Paraj Titum %A Joseph T. Iosue %A James R. Garrison %A Alexey V. Gorshkov %A Zhe-Xuan Gong %XThe study of quantum phase transitions requires the preparation of a many-body system near its ground state, a challenging task for many experimental systems. The measurement of quench dynamics, on the other hand, is now a routine practice in most cold atom platforms. Here we show that quintessential ingredients of quantum phase transitions can be probed directly with quench dynamics in integrable and nearly integrable systems. As a paradigmatic example, we study global quench dynamics in a transverse-field Ising model with either short-range or long-range interactions. When the model is integrable, we discover a new dynamical critical point with a non-analytic signature in the short-range correlators. The location of the dynamical critical point matches that of the quantum critical point and can be identified using a finite-time scaling method. We extend this scaling picture to systems near integrability and demonstrate the continued existence of a dynamical critical point detectable at prethermal time scales. Therefore, our method can be used to approximately locate the quantum critical point. The scaling method is also relevant to experiments with finite time and system size, and our predictions are testable in near-term experiments with trapped ions and Rydberg atoms.

%B Phys. Rev. Lett. %V 123 %8 9/11/2019 %G eng %U https://arxiv.org/abs/1809.06377 %N 115701 %R https://doi.org/10.1103/PhysRevLett.123.115701 %0 Journal Article %J Phys. Rev. Lett %D 2018 %T Asymmetric Particle Transport and Light-Cone Dynamics Induced by Anyonic Statistics %A Fangli Liu %A James R. Garrison %A Dong-Ling Deng %A Zhe-Xuan Gong %A Alexey V. Gorshkov %XWe study the non-equilibrium dynamics of Abelian anyons in a one-dimensional system. We find that the interplay of anyonic statistics and interactions gives rise to spatially asymmetric particle transport together with a novel dynamical symmetry that depends on the anyonic statistical angle and the sign of interactions. Moreover, we show that anyonic statistics induces asymmetric spreading of quantum information, characterized by asymmetric light cones of out-of-time-ordered correlators. Such asymmetric dynamics is in sharp contrast with the dynamics of conventional fermions or bosons, where both the transport and information dynamics are spatially symmetric. We further discuss experiments with cold atoms where the predicted phenomena can be observed using state-of-the-art technologies. Our results pave the way toward experimentally probing anyonic statistics through non-equilibrium dynamics.

%B Phys. Rev. Lett %V 121 %8 2018/12/20 %G eng %U https://arxiv.org/abs/1809.02614 %N 250404 %R https://doi.org/10.1103/PhysRevLett.121.250404 %0 Journal Article %J Physical Review Letters %D 2017 %T Entanglement area laws for long-range interacting systems %A Zhe-Xuan Gong %A Michael Foss-Feig %A Fernando G. S. L. Brandão %A Alexey V. Gorshkov %XWe prove that the entanglement entropy of any state evolved under an arbitrary 1/rα long-range-interacting D-dimensional lattice spin Hamiltonian cannot change faster than a rate proportional to the boundary area for any α > D + 1. We also prove that for any α > 2D + 2, the ground state of such a Hamiltonian satisfies the entanglement area law if it can be transformed along a gapped adiabatic path into a ground state known to satisfy the area law. These results significantly generalize their existing counterparts for short-range interacting systems, and are useful for identifying dynamical phase transitions and quantum phase transitions in the presence of long-range interactions.

%B Physical Review Letters %V 119 %P 050501 %8 2017/07/31 %G eng %U https://arxiv.org/abs/1702.05368 %N 5 %R 10.1103/PhysRevLett.119.050501 %0 Journal Article %J Physical Review Letters %D 2017 %T Fast State Transfer and Entanglement Renormalization Using Long-Range Interactions %A Zachary Eldredge %A Zhe-Xuan Gong %A Ali Hamed Moosavian %A Michael Foss-Feig %A Alexey V. Gorshkov %XIn short-range interacting systems, the speed at which entanglement can be established between two separated points is limited by a constant Lieb-Robinson velocity. Long-range interacting systems are capable of faster entanglement generation, but the degree of the speed-up possible is an open question. In this paper, we present a protocol capable of transferring a quantum state across a distance

Lieb and Robinson provided bounds on how fast bipartite connected correlations can arise in systems with only short-range interactions. We generalize Lieb-Robinson bounds on bipartite connected correlators to multipartite connected correlators. The bounds imply that an n-partite connected correlator can reach unit value in constant time. Remarkably, the bounds also allow for an n-partite connected correlator to reach a value that is exponentially large with system size in constant time, a feature which stands in contrast to bipartite connected correlations. We provide explicit examples of such systems.

%B Phys. Rev. A 96, 052334 %G eng %U https://arxiv.org/abs/1705.04355 %R https://doi.org/10.1103/PhysRevA.96.052334 %0 Journal Article %J Physical Review A %D 2017 %T Lieb-Robinson bounds on n-partite connected correlations %A Minh C. Tran %A James R. Garrison %A Zhe-Xuan Gong %A Alexey V. Gorshkov %XLieb and Robinson provided bounds on how fast bipartite connected correlations can arise in systems with only short-range interactions. We generalize Lieb-Robinson bounds on bipartite connected correlators to multipartite connected correlators. The bounds imply that an

Infinite-range interactions are known to facilitate the production of highly entangled states with applications in quantum information and metrology. However, many experimental systems have interactions that decay with distance, and the achievable benefits in this context are much less clear. Combining recent exact solutions with a controlled expansion in the system size, we analyze quench dynamics in Ising models with power-law (1/r α ) interactions in D dimensions, thereby expanding the understanding of spin squeezing into a broad and experimentally relevant context. In spatially homogeneous systems, we show that for small α the scaling of squeezing with system size is identical to the infinite-range (α = 0) case. This indifference to the interaction range persists up to a critical value α = 2D/3, above which squeezing degrades continuously. Boundaryinduced inhomogeneities present in most experimental systems modify this picture, but it nevertheless remains qualitatively correct for finite-sized systems.

%8 2016/12/22 %G eng %U https://arxiv.org/abs/1612.07805 %0 Journal Article %J Physical Review B %D 2016 %T Kaleidoscope of quantum phases in a long-range interacting spin-1 chain %A Zhe-Xuan Gong %A Mohammad F. Maghrebi %A Anzi Hu %A Michael Foss-Feig %A Philip Richerme %A Christopher Monroe %A Alexey V. Gorshkov %X Motivated by recent trapped-ion quantum simulation experiments, we carry out a comprehensive study of the phase diagram of a spin-1 chain with XXZ-type interactions that decay as 1/rα, using a combination of finite and infinite-size DMRG calculations, spin-wave analysis, and field theory. In the absence of long-range interactions, varying the spin-coupling anisotropy leads to four distinct phases: a ferromagnetic Ising phase, a disordered XY phase, a topological Haldane phase, and an antiferromagnetic Ising phase. If long-range interactions are antiferromagnetic and thus frustrated, we find primarily a quantitative change of the phase boundaries. On the other hand, ferromagnetic (non-frustrated) long-range interactions qualitatively impact the entire phase diagram. Importantly, for α≲3, long-range interactions destroy the Haldane phase, break the conformal symmetry of the XY phase, give rise to a new phase that spontaneously breaks a U(1) continuous symmetry, and introduce an exotic tricritical point with no direct parallel in short-range interacting spin chains. We show that the main signatures of all five phases found could be observed experimentally in the near future. %B Physical Review B %V 93 %P 205115 %8 2016/05/11 %G eng %U http://arxiv.org/abs/1510.02108 %N 20 %R http://dx.doi.org/10.1103/PhysRevB.93.205115 %0 Journal Article %J arXiv:1611.00797 %D 2016 %T Steady-state superradiance with Rydberg polaritons %A Zhe-Xuan Gong %A Minghui Xu %A Michael Foss-Feig %A James K. Thompson %A Ana Maria Rey %A Murray Holland %A Alexey V. Gorshkov %XA steady-state superradiant laser can be used to generate ultranarrow-linewidth light, and thus has important applications in the fields of quantum information and precision metrology. However, the light produced by such a laser is still essentially classical. Here, we show that the introduction of a Rydberg medium into a cavity containing atoms with a narrow optical transition can lead to the steady-state superradiant emission of ultranarrow-linewidth