Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session S35: General Quantum Information IIIRecordings Available

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Sponsoring Units: DQI Chair: TianXing Zheng, University of Chicago Room: McCormick Place W193B 
Thursday, March 17, 2022 8:00AM  8:12AM 
S35.00001: Deterministic Entanglement Transmission on SeriesParallel Quantum Networks XIANGYI MENG, Andrei E Ruckenstein, Shlomo Havlin, Jianxi Gao The performance of entanglement transmissionthe task of distributing entanglement between two arbitrarily distant nodes in a largescale quantum network (QN)is generally benchmarked against the classical entanglement percolation (CEP) scheme. Up to now, improvements of entanglement transmission beyond CEP have only been achieved, with great loss of generality, by nonscalable strategies and/or for restricted QN topologies. This talk explores a new and more effective mapping of QN, referred to as concurrence percolation theory (ConPT), that suggests using deterministic rather than probabilistic protocols for scalably improving on CEP across arbitrary QN topology. More precisely, we introduce a novel implementation of the ConPT mapping via a deterministic entanglement transmission (DET) scheme that is fully analogous to calculating the total resistance in resistor circuits, with the corresponding series and parallel rules represented by specific deterministic entanglement swapping and purification protocols, respectively. The DET is designed for general ddimensional information carriers and is scalable and adaptable for any seriesparallel QN, as it reduces the entanglement transmission task to a purely topological problem of calculating path connectivity. Unlike CEP, the DET displays different levels of optimality for generalized kconcurrencesa fundamental family of measures of bipartite entanglementon different QN topologies. More interestingly, our work implies that the wellknown nested purification repeater protocol does not optimize the final concurrence, a result that essentially relies on a special reverse arithmetic meangeometric mean (AMGM) inequality. 
Thursday, March 17, 2022 8:12AM  8:24AM 
S35.00002: Forced Entanglement of Circularly Polarized Photons Ian C Nodurft, Thomas A Searles, Brian T Kirby, Ryan T Glasser The Quantum Zeno effect reveals that a quantum system being continuously observed will have its natural timeevolution suppressed. More generally, the number of states accessible to the system is reduced depending on the type of measurement being performed. It is conceivable, therefore, that one might be able to "force" a group of particles into an entangled quantum state by restricting the system's access to only those states which compose an entangled state of a system. A numerical simulation is performed such that an unentangled pair of photons is evolved into a polarization entangled state. Beginning with one photon each of right and left circular polarization, the pair are sent through a pair of coupled waveguides in separate modes. The coupled waveguides cause the photons to gradually switch between modes with 4 possible states of the system; two in which the photons are in the same mode, bunched states, and two in which they are in opposite modes, unbunched states. Placing diamond configuration 4level absorbers in the path of both waveguides, bunched states are suppressed so the system only evolves between unbunched states. Appropriate choice of length for the coupled waveguides then leaves the photons in an entangled state at the output. 
Thursday, March 17, 2022 8:24AM  8:36AM 
S35.00003: Entanglement Negativity for Disjoint Intervals in the Ising and Free Compact Boson Conformal Field Theories Gavin Rockwood Entanglement negativity is a quantitative measure of entanglement between two parts of a system that is in a mixed state. For conformal field theories (CFTs), entanglement negativity captures fundamental characteristics of the CFT such as the central charge and operator content. In this work, we compute the replicated logarithmic negativity for multiple disjoint intervals for the Ising, free compactified boson, and the free fermion CFTs. In contrast to standard approaches using the correlation function of twist fields, our approach relies on exact computation of the partition function corresponding to theories on highergenus Riemann surfaces and is more suitable when the number of subsystems is larger than 2. We demonstrate that these partition functions are well behaved under changes in genus through smooth deformations of the intervals. Finally, we compare our results with numerical results obtained using the density matrix renormalization group technique for appropriate lattice regularizations of the CFTs. 
Thursday, March 17, 2022 8:36AM  8:48AM 
S35.00004: Quantum Entanglement from a Geometric prospective Shahabeddin Mostafanazhad aslmarand Entanglement is a key resource for quantum information processing. It is considered the most nonclassical manifestation of quantum mechanics and exhibits many strange features. For example, given an entangled quantum state, the knowledge of the whole system does not include the best possible knowledge of its parts, i.e. it can contain correlations that are incompatible with assumptions of classical theories of physics. Its strange behavior (Einstein's spooky action at a distance) is accompanied by its inherent complexity. This is why quantifying and detecting entanglement in large quantum systems is an open problem. We approach this challenge, not to develop a complete solution, but rather to glean deeper insights using novel geometric approaches that we have developed that build upon Schumacher's geometric Bell inequality. Perhaps by constructing wellmotivated entropicbased geometrical structures (e.g., areas, volumes ...), a set of trivial geometrical inequalities can reveal some of the complex properties of higherdimensional entanglement in highdimensional complex quantum networks. We provide numerous illustrative applications of this approach, and in particular to a random sample of a thousand density matrices. 
Thursday, March 17, 2022 8:48AM  9:00AM 
S35.00005: Entanglementassisted capacity regions and protocol designs for quantum multipleaccess channels Haowei Shi, MinHsiu Hsieh, Saikat Guha, Zheshen Zhang, Quntao Zhuang We solve the entanglementassisted (EA) classical capacity region of quantum multipleaccess channels with an arbitrary number of senders, which was conjectured by Hsieh, Devetak and Winter. As an example, we consider the bosonic Gaussian multipleaccess channel, which is prevalent in optical communications. For the total communication rate, we find that the EA capacity is additive and achieved by an entanglement source composed of senderreceiver pairwise twomode squeezed vacuum (TMSV) states; for the individual rates, we derive a computationally friendly outer bound for the EA capacity region. As an example, we evaluate the oneshot capacity region enabled by the pairwise TMSV states. The EA capacity region is strictly larger than the capacity region without entanglementassistance. Practical protocols based on pairwise TMSV states generated by spontaneous parametric downconversion, phase modulation and optical parametric amplifiers are presented to benefit from entanglement. In the parameter region of a large noise background, the receivers can enable a simultaneous rate advantage of 82.0% for each sender. Due to teleportation and superdense coding, our results for EA classical communication can be directly extended to EA quantum communication at half of the rates. 
Thursday, March 17, 2022 9:00AM  9:12AM 
S35.00006: Entanglement Phases in largeN hybrid Brownian circuits with longrange couplings Subhayan Sahu, ShaoKai Jian, Gregory Bentsen, Brian Swingle We study measurementinduced phases and transitions in tractable largeN models, including a Brownian qubit model and a Brownian SYK model, in the presence of longrange couplings which decay as a power law, with α being the powerlaw exponent. In one dimension and in interacting models, the longrange coupling is irrelevant for α>3/2, thus the volumelaw and arealaw entanglement phases and the phase transition remain similar to the shortranged case. For α<3/2 the longrange coupling is relevant and leads to a nontrivial dynamical exponent at the measurementinduced phase transition. More interestingly, for α<1 the entanglement pattern receives a subvolume correction for both arealaw and volumelaw phases. The volumelaw phase with such a subvolume correction realizes a novel quantum error correcting code whose code distance scales as L^{22α}. We extend the calculation in a quadratic Brownian SYK model to study the phase diagram of the longrange free fermion model under monitoring, and we find that two distinct fractal entangled phases emerge when α is sufficiently low. 
Thursday, March 17, 2022 9:12AM  9:24AM 
S35.00007: Cliffordinvariant additive measure for fermionic correlations Yaroslav Herasymenko Quantifying correlations in manybody systems can be crucial for the analysis and approximate simulations of condensed matter systems. As a prominent example, entanglement entropy has useful scaling properties and forms the basis for tensor network methods. Entanglement measures for fermionic systems, however, are highly sensitive to Clifford (singleparticle) rotations, even though these do not contain any quantum complexity. To address this issue, we introduce an explicit measure for fermionic correlations related to the Plucker identities that we dub Plucker entropy. This measure is invariant with respect to Clifford rotations and obeys additivity, giving rise to entropylike scaling properties. We study Plucker entropy numerically as applied to the lowenergy physics of the Hubbard model, capturing the absence of correlations both in its free fermion and its Mott insulator regimes. Furthermore, we analyze Plucker entropy as a resource for fermionic Clifford computations ("quantum magic"). Inspired by the connection between entanglement entropy and tensor networks, potential applications to approximate classical methods are discussed. 
Thursday, March 17, 2022 9:24AM  9:36AM 
S35.00008: Stabilizer Rényi entropy Lorenzo Leone, Alioscia Hamma Although quantum entanglement is a paradigmatic feature of quantum states, it is well known that stabilizer states, possessing volume law of entanglement, can be efficiently simulated on a classical computer. Thus, to unlock the exponential quantum advantage, nonstabilizer states (also dubbed as magic states) constitute an essential ingredient for quantum computation. I will introduce a resource theoretic measure of magic in quantum states called Stabilizer Rényi entropy. Being easily manageable and computable, it is shown to possess a tight connection with Out of Time Order Correlation functions (OTOCs), displaying an intriguing relation between the resource theory of magic and quantum chaos. 
Thursday, March 17, 2022 9:36AM  9:48AM 
S35.00009: Experimental quantum communication enhancement by superposing trajectories Lee A Rozema, Giulia Rubino, Philip Walther In quantum communication networks, wires represent welldefined trajectories along which quantum systems are transmitted. In spite of this, trajectories can be used as a quantum control to govern the order of different noisy communication channels, and such a control has been shown to enable the transmission of information even when quantum communication protocols through welldefined trajectories fail. This result has motivated further investigations on the role of the superposition of trajectories in enhancing communication, which revealed that the use of quantum control of parallel communication channels, or of channels in series with quantumcontrolled operations, can also lead to communication advantages. Building upon these findings, here we experimentally and numerically compare different ways in which two trajectories through a pair of noisy channels can be superposed. We observe that, within the framework of quantum interferometry, the use of channels in series with quantumcontrolled operations generally yields the largest advantages. Our results contribute to clarify the nature of these advantages in experimental quantumoptical scenarios and showcase the benefit of treating the trajectory of the information carriers as quantum. 
Thursday, March 17, 2022 9:48AM  10:00AM 
S35.00010: Entanglement Detection of Multiphoton States Madhura Ghosh Dastidar, Gniewomir Sarbicki Multiparticle entangled states cannot be characterized easily by conventional quantum state tomography due to the requirement of a large number of measurements for reconstructing the corresponding density matrix [1]. Therefore, it is essential to identify certain observables called entanglement witnesses whose expectation values provide a test for entanglement of such manybody states and is measured like a Bell inequality. For photonic states, another challenge is to inculcate the practical limitations of photodetection mechanisms that hinder numberresolved measurements of a single pulse [2]. Here we present a theoretical scheme for experimental verification of entanglement in infinitedimensional multiphotonic states without performing a full state tomography. Our proposed experiment involves a reduced Hilbert space where the photonic state is either detected or not detected by the photodetectors, thereby reducing the dimensionality of our problem. Further, we elucidate the observables for testing entanglement and their associated entropic uncertainties to quantify the resolution of the measurements. 
Thursday, March 17, 2022 10:00AM  10:12AM 
S35.00011: Entanglement entropy in the Ising conformal field theory with topological defects Hubert Saleur, Ananda Roy Entanglement entropy (EE) in conformal field theories (CFTs) contains signatures of the universal characteristics of the CFTs. The existence of boundaries and defects in the CFT leads to universal contributions to the EE which can be used to identify these features of the theory. In this work, we investigate EE of a subsystem in the Ising CFT in the presence of a topological defect. The latter is the purely transmitive case of the more general conformal defect and is deeply related to the internal symmetries of the CFT. We demonstrate that the behavior of the EE depends crucially on geometric arrangement of the subsystem with respect to the defect, in particular, whether the defect lies within the subsystem or precisely at the edge of the subsystem, with rather unexpected results for the latter case. We show that the topological defect necessarily comes in conjunction with zeroenergy modes. We quantify the nontrivial subleading contributions to the EE arising due to these zeromodes when the subsystem size is a finite fraction of the total system size. We perform these computations starting from an appropriate lattice model and mapping the defect Hamiltonian to a freefermion model using JordanWigner transformation. 
Thursday, March 17, 2022 10:12AM  10:24AM 
S35.00012: Entanglement entropy in (2+1)dimensional quantum field theories Qicheng Tang, Wei Zhu We develop a method to calculate the entanglement entropy for (2+1)D quantum field theories, by representing the 3D replicated Green's function in term of an infinite series of the connected diagrams in 2D replica spacetime manifold. Within this framework, an exact derivation of the arealaw entanglement entropy for (2+1)D free scalar and Dirac fields is provided. Moreover, our method guides a perturbative approach to interacting theories, by considering the interaction as a correction to the 2D replicated twopoint function. Especially, our method allows an explicit calculation of the entanglement entropy in disordered system. We discuss the case of a (2+1)D Dirac filed under a static random gauge field as a concrete example. The corresponding lattice simulation gives consistent results with our analytical solution, indicates the ability of our method to capture ultraviolet behaviors of entanglement entropy in generic interacting field theories. 
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