Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session R28: Distributed Quantum Computation, Networking and Information Security IIFocus

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Sponsoring Units: DQI Chair: Victoria Lipinska, Delft University of Technology Room: BCEC 161 
Thursday, March 7, 2019 8:00AM  8:12AM 
R28.00001: Entanglement cost of quantum state preparation and channel simulation Xin Wang, Mark M Wilde We study various aspects of the entanglement cost of quantum state preparation and quantum channel simulation. First, we establish that the exact entanglement cost of any bipartite quantum state under PPTpreserving operations is given by a singleletter formula, here called the κentanglement of a quantum state. This formula is calculable by a semidefinite program, thus allowing for an efficiently computable solution for general quantum states. Notably, this is the first time that an entanglement measure for general bipartite states has been proven not only to possess a direct operational meaning but also to be efficiently computable, thus solving a question that has remained open since the inception of entanglement theory over two decades ago. Second, we study the exact entanglement cost of quantum channel simulation in the parallel setting. In particular, the largest κentanglement that can be established via a quantum channel remarkably gives a singleletter formula for the exact parallel PPTentanglement cost of simulating this channel, and it is also efficiently computable by a semidefinite program. 
Thursday, March 7, 2019 8:12AM  8:24AM 
R28.00002: Communicating via Ignorance KAUMUDIBIKASH GOSWAMI, Jacquiline Romero, Andrew White Communication through a sequence of two identical, noisy, depolarising channels is impossible in conventional information theory. Surprisingly, it has been shown in the paper [1] communication becomes possible if the depolarising channels are within a quantum switch, where the order of the channels is in a quantum superposition [2,3]. We experimentally demonstrate this counterintuitive result in a quantum switch that uses polarisation to coherently control the order of two depolarising channels acting on the transverse spatial mode of a photon. We send (3.41±0.15)×10^{2 }bits of information through two fully depolarising channels that are in an indefinite causal order. [4] 
Thursday, March 7, 2019 8:24AM  8:36AM 
R28.00003: Quantum Link Prediction in Complex Networks Yasser Omar, João Moutinho, André Melo, Bruno Coutinho, Istvan Kovacs, Albert Barabasi Predicting the existence of a link in a complex network is a nontrivial task, namely for large social and biological networks, with important applications. Experiments to map the full structure of biological networks (e.g. proteinprotein interactions) are very challenging, costly and time consuming, and large amounts of data is still missing. Link prediction methods are not only a key computational tool to aid these efforts in understanding complex biological systems, but also very useful for other studies of timevarying complex networks, as for example social networks. 
Thursday, March 7, 2019 8:36AM  8:48AM 
R28.00004: Indefinite Causal Order Jacquiline Romero, Kaumudikash Goswami, Christina Giarmatzi, Michael Kewming, Fabio Costa, Cyril Branciard, Andrew White Quantum mechanics allows events to happen with no definite causal order: this can be verified by measuring a causal witness, in the same way that an entanglement witness verifies entanglement. 
Thursday, March 7, 2019 8:48AM  9:00AM 
R28.00005: Counterfactual Quantum Superdense Coding Fakhar Zaman, Youngmin Jeong, Hyundong Shin Quantum superdense coding (QSC) ) is one of the most striking effects in quantum communication. It enables one to transmit a twobit classical message by sending only one qubit using initially shared entanglement. In this article, we present a counterfactual QSC scheme that enables remote parties to accomplish this task without prior entanglement but no physical particle is found in the transmission channel. We consider two remote parties, namely Alice (sender) and Bob (receiver), have untangled particlesan electron and a photon. First, we generate entanglement between the electron and photon without transmitting any physical particle over the channel. Alice performs one of the four unitary operations μ ∈ {Ι, σ_{x}, σ_{Y}, σ_{Z }} on her entangled particle. Instead of transmitting her entangled particle to Bob, Alice and Bob perform counterfactual Bellstate analysis based on the chained quantum Zeno effect to distinguish between the four Bellstates under local operations and enable Bob to decode the twobit classical message. 
Thursday, March 7, 2019 9:00AM  9:12AM 
R28.00006: Dronebased Quantum Key Distribution Andrew Conrad, Dalton Chaffee, Joseph Chapman, Chris Chopp, Kyle Herdon, Alexander Hill, Daniel SanchezRosales, Joseph Szabo, Daniel J Gauthier, Paul G Kwiat Recent advances in quantum memories point to the future viability of quantum networking, including quantum cryptography. To be truly multipurpose, future quantum communication networks should consist of a variety of platforms, e.g., airplanes, drones, and ships, though the motion of these platforms precludes the use of fiberbased approaches to quantum cryptography; freespace quantum key distribution (QKD) systems have historically been rather bulky. Small moving platforms, such as multirotor drones, are ideal for reconfigurable networks in both urban and rural environments but are only capable of supporting lightweight payloads (< 10 kg). Here we discuss our current progress in developing a reconfigurable network of two or more small multirotor drones implementing a modified BB84 quantum key distribution protocol over a freespace optical channel. This requires the development of fast and lightweight sources of polarized photons with no side channel leakage, miniaturization of timetagging electronics and singlephoton detectors, and the development of a robust signal acquisition and pointing and tracking system. 
Thursday, March 7, 2019 9:12AM  9:48AM 
R28.00007: Quantum Internet Applications Invited Speaker: Marc Kaplan In this talk, we will discuss the application layer of a quantum internet. In such a network, the nodes are connected by quantum communication links, and can altogether be in an arbitrary entangled state. This allows the network to run a wide range of application, much beyond quantum key distribution, the main application of current quantum communication networks. 
Thursday, March 7, 2019 9:48AM  10:00AM 
R28.00008: QuantumAssisted Telescope Arrays Emil Khabiboulline, Johannes Borregaard, Kristiaan De Greve, Mikhail Lukin Quantum networks provide a platform for astronomical interferometers capable of imaging faint stellar objects. We present a protocol with efficient use of quantum resources and modest quantum memories. In our approach, the quantum state of incoming photons along with an arrival time index is stored in a binary qubit code at each receiver. Nonlocal retrieval of the quantum state via entanglementassisted parity checks at the expected photon arrival rate allows for direct extraction of phase difference, effectively circumventing transmission losses between nodes. Compared to prior proposals, our scheme, based on efficient quantum data compression, offers an exponential decrease in required entanglement bandwidth. We show that it can be operated as a broadband interferometer and generalized to multiple nodes. We also analyze how imaging based on the quantum Fourier transform provides improved signaltonoise ratio compared to classical processing. Finally, we discuss physical realizations including photon detectionbased quantum state transfer. Experimental implementation is then feasible with nearterm technology, enabling optical imaging of astronomical objects akin to wellestablished radio interferometers and pushing resolution beyond what is practically achievable classically. 
Thursday, March 7, 2019 10:00AM  10:12AM 
R28.00009: Long distance measurementdeviceindependent quantum key distribution without reference calibration HongWei Liu, JiPeng Wang, HaiQiang Ma, ShiHai Sun Referenceframeindependent measurementdeviceindependent quantum key distribution (RFIMDIQKD) can reduce the complexity of practical systems caused by the alignment of the reference frame. Lengthening the transmission distance and improving the system clock rate are essential in practical applications of QKD. Herein, in an asymptotic case, we report the results of RFIMDIQKD over a distance of 160 km at a clock rate of 50 MHz. By considering the statistical fluctuation of a finite key, we experimentally implemented a fourintensity decoystate RFIMDIQKD protocol with biased bases at transmission distances of 100 km and 120 km. In addition, we compare the RFIMDIQKD protocol with the original MDIQKD protocol when different isalignments of the reference frame are deployed. The results demonstrate the robustness of our scheme and that the key rate of RFIMDIQKD can be improved for a large misalignment of the reference frame. 
Thursday, March 7, 2019 10:12AM  10:24AM 
R28.00010: Entangledpulse generation inside coherent Ising machines using entanglement swapping Ryotatsu Yanagimoto, Peter McMahon, Tatsuhiro Onodera, Edwin Ng, Hideo Mabuchi Coherent Ising machines (CIMs) have been proposed and demonstrated as heuristic solvers of hard combinatorial optimization problems. In current measurementfeedbackbased CIMs (P.L. McMahon 2016), interactions between pulses (spins) are mediated via a classical feedback mechanism, and consequently no entanglement among pulses is generated. In this research, we investigate the use of entanglement swapping to introduce interpulse entanglement into such CIMlike architectures, using an external source of independently squeezed pulses. We develop models to describe the resulting intracavity dynamics as a function of system parameters, which can be numerically simulated to characterize the quantum noise and correlations in the pulse train. We also introduce and employ several measures of inseparability to quantify the nonclassical correlations that are realized. Analyzing these measures reveal tradeoffs between system parameters and produce metrics useful for optimizing them. We present the requirements necessary to realize experimentally desirable levels of nonclassical correlations. 
Thursday, March 7, 2019 10:24AM  10:36AM 
R28.00011: Maximal LELM Distinguishability of Qubit and Qutrit Bell States using Projective and NonProjective Measurements Nathaniel Leslie, Julien Devin, Theresa W Lynn Numerous quantum information protocols make use of maximally entangled twoparticle states, or Bell states, in which information is stored in the correlations between the two particles rather than their individual properties. Retrieving information stored in this way means distinguishing between different Bell states, yet the well known nogo theorem establishes that projective linear evolution and local measurement (LELM) detection schemes can only reliably distinguish three of the four qubit Bell states. We present newlyestablished maximum distinguishability bounds for the qutrit Bell states of bosons via projective LELM measurements; only three of the nine Bell states can be distinguished. Next, we extend to the case of nonprojective measurements. We present a strengthened nogo theorem, which shows that general LELM measurements cannot reliably distinguish all four qubit Bell states. We also establish that at most five qutrit Bell states can be distinguished with generalized LELM measurements. 
Thursday, March 7, 2019 10:36AM  10:48AM 
R28.00012: Generating accessible entanglement in bosons via paircorrelated tunneling Tyler Volkoff, Chris Herdman We consider an extended BoseHubbard model that includes paircorrelated tunneling. We demonstrate that a minimal fourmode implementation of this model exhibits a paircorrelated regime in addition to Mott insulator and superfluid regimes. We propose a low complexity variational subspace for the ground state of the system in the paircorrelated regime, which we find to be numerically exact in pure pairtunneling limit. Additionally, we propose a parameterfree high fidelity model wave function that qualitatively captures the features of the ground state in the paircorrelated regime. Due to particle number conservation, the operationally accessible entanglement vanishes deep inside the Mott insulator and superfluid regimes, however in the pure paircorrelated tunneling limit we find that the accessible entanglement entropy grows logarithmically with the number of particles. Additionally, we demonstrate that upon application of a unitary beamsplitter operation, the paircorrelated ground state is transformed into a state with completely accessible entanglement that is not limited by superselection rules. 
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