Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session P30: General Quantum Information: Entanglement, Complexity, and RandomnessLive
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Sponsoring Units: DQI Chair: Timothy Proctor, Sandia National Laboratories |
Wednesday, March 17, 2021 3:00PM - 3:12PM Live |
P30.00001: A numerical study of entanglement measures of clusters joined by a point contact Alyssa Horne, Barry Friedman The ground state of an antiferromagnetic Heisenberg model on L X L clusters joined by a single bond and balanced Bethe clusters are investigated with quantum Monte Carlo. The improved Monte Carlo method of Sandvik and Evertz is used and the observables include valence bond and loop valence bond observables introduced by Lin and Sandvik as well as the valence bond entropy and the second Renyi entropy. For the bisecting of the Bethe cluster, in disagreement with our previous results and in agreement with mean field theory, the valence loop entropy and the second Renyi entropy scale as the log of the number of sites in the cluster. For bisecting the L X L - LX L clusters, all the observables appear to scale as L in agreement with our previous results. This is in disagreement with a straight forward application of the area law. |
Wednesday, March 17, 2021 3:12PM - 3:24PM Live |
P30.00002: Entanglement of formation and quantum discord in multipartite j-spin coherent states. Hasnaa Baba, Mohammed Daoud We study the entanglement of formation and the quantum discord contained in even and odd multipartite j-spin coherent states. The key element of this investigation is the fact that a single j-spin coherent state is viewed as comprising 2j qubit states. We compute the quantum correlations present in the n even and odd j-spin coherent states by considering all possible bipartite splits of the multipartite system. We discuss the different bi-partition schemes of quantum systems and we examine in detail the conservation rules governing the distribution of quantum correlations between the different qubits of the multipartite system. Finally, we derive the explicit expressions of quantum correlations present in even and odd spin coherent states decomposed in four spin sub-systems. We also analyze the properties of monogamy and we show in particular that the entanglement of the formation and the quantum discord obey the relation of monogamy only for even multipartite j-spin coherent states. |
Wednesday, March 17, 2021 3:24PM - 3:36PM Live |
P30.00003: Two-dimensional entanglement entropy with chemical potential and topological Wilson loops Bom Soo Kim We compute the entanglement and Renyi entropies for Dirac fermions on a 2 dimensional torus in the presence of chemical potential, current source, and topological Wilson loops. These gauge fields are unified in a single framework by exhausting all the ingredients of the electromagnetic vertex operators of the Zn orbifold conformal field theory. |
Wednesday, March 17, 2021 3:36PM - 3:48PM Live |
P30.00004: Entanglement enhancement in two-dimensional spin system coupled to a thermal dissipative environment in an inhomogeneous magnetic field. Gehad Sadiek, Samaher Almalky Recently there has been great interest in studying unconventional magnetism in spin systems in the absence and presence of dissipative effects. Furthermore, many of the newly engineered quantum systems such as cold atoms in optical lattices, optical microcavities, trapped ions and superconducting circuits, represent great experimental framework for studying dissipative effects in driven many-body quantum systems. In this work, we study the time evolution and the asymptotic steady state of the bipartite quantum entanglement and spin relaxation in a finite two-dimensional triangular Heisenberg spin -1/2 lattice under the influence of dissipative Lindblad environment at zero and finite temperature. We show how a particular inhomogeneous magnetic field setup, where the gradient is directed toward the central spin, can significantly enhance the bipartite and global bipartite entanglement among the nearest neighbor spins and boost their thermal robustness in the completely anisotropic (Ising) system and even the beyond nearest neighbors in the partially anisotropic system, signaling a long range quantum correlation and consequently a critical behavior across the system. |
Wednesday, March 17, 2021 3:48PM - 4:00PM Live |
P30.00005: Entanglement Between Orbitals Lexin Ding, Zoltán Zimborás, Christian Schilling Entanglement is one of the most fascinating concepts of modern physics. In striking contrast to its abstract and mathematical foundation, its practical side is remarkably underdeveloped: Even for the simplest scenario of just two orbitals or sites (“Hubbard dimer”) no faithful measure for generic mixed quantum states is known. By exploiting the spin symmetries of realistic electronic systems and implementing the fundamental superselection rule we succeed in deriving a compact formula for the relative entropy of entanglement between any two electronic orbitals. As a proof of concept, its first application already reveals a couple of striking insights: (i) The orbital correlation in molecular systems is mainly classical, rasing questions about the significance of entanglement for chemical bonding, (ii) the entanglement between most sites in the Hubbard model vanishes entirely, (iii) a local Fermi level-like structure can be restored within DMRG for off-lattice based on the division of correlation into its classical and quantum parts. |
Wednesday, March 17, 2021 4:00PM - 4:12PM Live |
P30.00006: Multiregion entanglement in locally scrambled quantum dynamics Ahmed Akhtar, Yizhuang You We study the evolution of multi-region bipartite entanglement entropy under locally scrambled quantum dynamics and show that it can significantly modify the growth of single-region entanglement. We developed a novel theoretical framework, called the entanglement feature formalism, to organize all the multi-region entanglement systematically as a sign-free many-body state. We further propose a two-parameter matrix product state (MPS) ansatz to efficiently capture the exponentially many multi-region entanglement features. Using these tools, we are able to study the dynamics of the full entanglement spectrum and represent the evolution in the MPS parameter space. By comparing the dynamical constraints on the motion of entanglement cuts, we are able to identify different quantum dynamics models in a unifying entanglement feature Hamiltonian and calculate quantities such as the operator-averaged out-of-time-order correlator, butterfly and entanglement velocities. We find that multi-region effects only vanish for Haar random circuits. These developments could enable more efficient numerical simulations and more systematic theoretical understandings of the multi-region entanglement dynamics in quantum many-body systems. |
Wednesday, March 17, 2021 4:12PM - 4:24PM Live |
P30.00007: Mueasurement-induced randomness in measured qubit processes Ariadna Venegas-Li, James Crutchfield We discuss the effects of quantum measurement in a time series of qubits. We show that measurement generally induces high complexity in the observed classical time series and can both increase or decrease the inherent randomness (Shannon entropy rate) of the observed classical process with respect to the underlying stochastic process of qubits. We identify nonorthogonality of the qubit states as the mechanism underlying the resulting complexities and examine the influence of measurement choices on the randomness and structure of the measured qubit process. We discuss measurement choices of potential interest in gaining insight about the underlying time series of qubits. |
Wednesday, March 17, 2021 4:24PM - 4:36PM Live |
P30.00008: Detecting Randomness and Structure in Quantum Processes David Gier, James P Crutchfield Many quantum phenomena—quantum communication protocols, blinking quantum dots, cavity QED sources—generate sequential entangled qudits, which we call quantum stochastic processes. In an effort to understand their information content and correlation, we develop a framework for stationary, ergodic quantum processes and define quantum information properties related to the von Neumann entropies of sequential qudit blocks. Qudit blocks can exhibit both purely-classical and uniquely-quantum correlations. Applying sequential measurements yields classical stochastic processes whose informational properties are bounded by those of the underlying quantum process. The type of measurement—projective or POVM, single- or joint-qudit basis, fixed basis or adaptive measurement protocol—determine how structured the underlying process appears to an experimenter whose only access is via measurements. We detail examples with short- and long-range entanglement, as well as a variety of correlational structures determined by specific Hamiltonian dynamics. |
Wednesday, March 17, 2021 4:36PM - 4:48PM Live |
P30.00009: Implementation of general quantum measurements using only a single ancillary qubit and postselection TANMAY SINGAL, Filip Maciejewski, Michal Oszmaniec With the aim to reduce resources for near-term quantum computers, we propose a scheme to implement a general quantum measurement (POVM) in dimension d using only classical resources and a single ancillary qubit. This method is based on probabilistic implementation of d-outcome POVMs, which is followed by postselection on some of the outcomes. In an earlier work, a similar scheme requiring no ancillary qubits was proposed, and its success probability scaled as 1/d. Contrastingly, for Haar random rank-one POVMs with at most d^2 outcomes, our scheme's success probability doesn't go to zero with d. We conjecture that this is true for all POVMs in dimension d. Numerical computations showing constant success probability for SIC-POVMs in dimension up to 323, support this conjecture. Additionally, for the gate noise model used in the recent demonstration of quantum computational advantage (https://www.nature.com/articles/s41586-019-1666-5), it's shown that noise compounding in circuits which implement Haar-random POVMs by our scheme is substantially lower than the scheme that directly uses Naimark’s dilation theorem. |
Wednesday, March 17, 2021 4:48PM - 5:00PM Live |
P30.00010: Observation of interaction induced Rydberg blockade and local spin freezing in an NMR quantum simulator Krithika V R, Soham Pal, Rejish Nath, Mahesh T S We experimentally emulate interaction induced blockade and local spin freezing in two and three spin-1/2 nuclear spin-systems using Nuclear Magnetic Resonance (NMR) architecture. These phenomena are identical to the Rydberg blockade and Rydberg biased freezing, which are facilitated by strong inter-particle interactions. In addition, we probe quantum correlations between the qubits under blockade and freezing phenomena using quantum discord. Such studies open up interesting quantum-information perspectives in simulating atomic interactions via NMR architecture. |
Wednesday, March 17, 2021 5:00PM - 5:12PM Live |
P30.00011: Quantum operator growth bounds for kicked tops and semiclassical spin chains Chao Yin, Andrew Lucas We prove bounds on infinite temperature out-of-time-ordered correlation functions in semiclassical spin models, where each site contains a large-S spin degree of freedom. Focusing on the dynamics of a single spin, we prove the finiteness of the Lyapunov exponent in the large-S limit, and numerically find our upper bound on Lyapunov exponents can be within an order of magnitude of numerically computed values in classical and quantum kicked top models. Generalizing our results to coupled large-S spins on lattices, we prove that the butterfly velocity, which characterizes the spatial speed of quantum information scrambling, is finite in the large-S limit. Our work demonstrates how to derive rigorous constraints on quantum dynamics in a large class of models where conventional Lieb-Robinson bounds are not useful. We emphasize qualitative differences between semiclassical large-spin models, and quantum holographic systems including the Sachdev-Ye-Kitaev model. |
Wednesday, March 17, 2021 5:12PM - 5:24PM Live |
P30.00012: Model-Independent Simulation Complexity of Complex Quantum Dynamics Aiman Khan, David Quigley, Max Marcus, Erling Thyrhaug, Animesh Datta We present a model-independent measure of dynamical complexity based on simulation of complex quantum dynamics using stroboscopic Markovian dynamics. Tools from classical signal processing enable us to infer the Hilbert space dimension of the complex quantum system evolving under a time-independent Hamiltonian via pulsed interrogation. We illustrate this using simulated third-order pump-probe spectroscopy data for exciton transport in a toy model of a coupled dimer with vibrational levels, revealing the dimension of the singly-excited manifold of the dimer. Finally, we probe the complexity of excitonic transport in light harvesting 2 (LH2) and Fenna-Matthews-Olson (FMO) complexes using data from two recent nonlinear ultrafast optical spectroscopy experiments. For the latter we make model-independent inferences that are commensurate with model-specific ones, including the estimation of the fewest number of parameters needed to fit the experimental data and identifying the spatial extent, i.e., delocalization size, of quantum states participating in this complex quantum dynamics. |
Wednesday, March 17, 2021 5:24PM - 5:36PM Live |
P30.00013: Quantum Gravity in the Lab Sepehr Ghazi Nezami, Adam R Brown, Hrant Gharibyan, Stefan Leichenauer, Henry W Lin, Grant Salton, Leonard Susskind, Brian Swingle, Michael Walter With the long-term goal of studying quantum gravity in the lab, we propose holographic teleportation protocols that can be readily executed in table-top experiments. These protocols exhibit similar behavior to that seen in recent traversable wormhole constructions: information that is scrambled into one half of an entangled system will, following a weak coupling between the two halves, unscramble into the other half. We introduce the concept of "teleportation by size" to capture how the physics of operator-size growth naturally leads to information transmission. The transmission of a signal through a semi-classical holographic wormhole corresponds to a rather special property of the operator-size distribution we call "size winding". |
Wednesday, March 17, 2021 5:36PM - 5:48PM Live |
P30.00014: Geometrical Equivalence Of Entanglement Shahabeddin Mostafanazhad aslmarand, Warner A. Miller n this paper, we propose a novel way for coarse-graining entanglement in quantum networks; this unique geometrical approach will enable us to differentiate systems with high quantum correlation from systems with low quantum correlation. We will show using this geometrical approach to quantum entanglement; one can address the entanglement between specific parts of the quantum network without the necessity to calculate all pairwise entanglement between nodes in the network. We will also show that for particular quantum networks, this geometrical approach will be the geometrical realization of squashed entanglement. Our approach is inspired by Schumacher’ssinglet state triangle inequality, which used an information geometry-based entropic distance, but unlike Schumacher, which used classical entropy, we will not only use proper quantum entropy to reach a new inequality but will also generalize this inequality to inequalities for areas and volumes and higher dimensional volumes for multipartite quantum systems. |
Wednesday, March 17, 2021 5:48PM - 6:00PM Live |
P30.00015: Robust quantum computational advantage using fermionic linear optics and magic input states Michał Oszmaniec A fermionic analogue of Boson Sampling, known as Fermionic Linear Optics (FLO), is a restricted model of quantum computation which is known to be efficiently classically simulable. We show that, when initialized with suitable input states, FLO circuits can be used to demonstrate quantum computational advantage. We consider particle-number conserving (passive) FLO, and active FLO, also known as Matchgate circuits. We prove anticoncentration for probabilities in random FLO circuits. We also show robust average-case hardness of computation of probabilities in our scheme. We achieve this by adopting to representations of Lie groups the worst-to average-case reduction by Movassagh. These findings give together hardness guarantees matching that of the Random Circuit Sampling and surpassing Boson Sampling. Our scheme is experimentally feasible. FLO circuits are relevant for quantum chemistry and many-body physics, and have been successfully implemented in the superconducting architectures. Preparation of the desired input state is done by a simple shallow and parallelizable circuit. We also argue that due to the structured nature of FLO circuits, they can be efficiently certified using resources scaling polynomially with the system size. |
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