Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session Q70: Quantum Network Algorithms and Analysis |
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Sponsoring Units: DQI Chair: David Bernal Neira, USRA - Univ Space Rsch Assoc Room: Room 409 |
Wednesday, March 8, 2023 3:00PM - 3:12PM |
Q70.00001: Paving the Way Towards 800 Gbps Quantum-Secured Optical Channel Deployments in Mission-Critical, Real-World Environments Omar Amer, Marco Pistoia, Monik R Behera, Joseph A Dolphin, James Dynes, Benny John, Paul A Haigh, Yasushi Kawakura, David H Kramer, Jeffery Lyon, Navid Moazzami, Tulasi D Movva, Antigoni Polychroniadou, Suresh X Shetty, Greg Sysak, Farzam Toudeh-Fallah, Sudhir Upadhyay, Robert I Woodward, Andrew J Shields Since its inception almost four decades ago, quantum cryptography has matured into a well-developed, practical field of research. In parallel, the development of cryptographically relevant quantum computers on the horizon threatens the security of today's asymmetric cryptographic systems, and therefore the security of today's information infrastructure. While so-called "post-quantum" public key schemes may prove to be sufficient for many applications, they necessarily rely on certain complexity theoretic assumptions, leaving open the possibility that future advances in complexity theory could break these systems. Quantum key distribution, by contrast, can be used to achieve information theoretic, unconditional security by relying on the principles of quantum mechanics in place of computational assumptions, making it an attractive, future-proof option for high-risk sensitive communications. In this work, we demonstrate the validity of quantum key distribution at industry scale. We report on the successful deployment of QKD devices into a replica environment of JPMorgan Chase's Data Center Interconnect network. The QKD links were established, to our knowledge for the first time, over a single fiber with multiple high capacity Dense Wavelength Division Multiplexed (DWDM) channels. These high capacity channels included an 800 Gbps quantum-secured channel carrying data encrypted by the symmetric keys generated by the system, as well as 1.6 Tbps of additional traffic. This high capacity link was established at distances up to 100 km while maintaining secret key rates that could supply 258 separate AES-256-GCM encrypted channels with a key refresh rate of 1/sec. In real-world deployments, the ability to use a single fiber to establish the quantum channel and the DWDM channels is of the utmost importance as dark fiber is a valuable commodity. Of course, there are complications inherent in multiplexing the fragile quantum signal with high-capacity DWDM channels. In our work, we quantify the impact of these complications, as well as a number of realistic factors inherent to real-world deployments. Finally, we compare and contrast the results we achieve with previous works investigating real-world and multiplexed deployments of QKD, as well as theoretical results in those areas. |
Wednesday, March 8, 2023 3:12PM - 3:24PM |
Q70.00002: Scheduling Quantum Teleportation in Noisy Memories Aparimit Chandra, Wenhan Dai, Don Towsley Quantum teleportation is a key application provided by quantum networks. Unfortunately, teleportation requires the distribution of an entangled state between two nodes which is a probabilistic process. This results in delays as the qubit to be teleported is stored in memory while it waits for an EPR pair. These delays cause fidelity loss as the qubit is continuously decohering while it is in memory. The node then has a choice of which qubit to teleport first which gives rise to a scheduling problem. This work quantifies the fidelity loss at a node in a quantum network due to storage in noisy memory platforms. We also explore the effects of different scheduling policies on fidelity. The memory platform is parameterized by decoherence rate and buffer size. We give closed-form analytical expressions for calculating the average fidelity with respect to the load, buffer size, and decoherence rate of the memory platform for different scheduling policies. We prove that serving the youngest qubits first with pushout for buffer overflow management maximizes average fidelity and is an optimal scheduling policy for exponential decay noise models. We also extend this model to calculate the average fidelity of the end-to-end entanglement produced by a quantum repeater between two nodes. |
Wednesday, March 8, 2023 3:24PM - 3:36PM |
Q70.00003: Performance of quantum network applications utilising multiple contemporaneous quantum resources Bethany Davies, Gayane Vardoyan, Stephanie Wehner We study the performance of contemporaneous quantum resource establishment between two distant nodes which are components of a near-term quantum network, enabling the two parties to attempt bipartite entanglement generation in a sequential manner. Each resource is created using the successfully generated entangled pairs and is subject to a lifetime limit, known as a cut-off, which triggers resource expiration -- possibly on both sides of the link -- causing a reset of the corresponding qubits. To carry out the execution of certain distributed quantum applications, the parties must be able to generate all quantum resources within the time window specified by this cut-off on qubit storage. For both a finite and infinite window cut-off, we utilise methodology from sequential window problems and scan statistics literature to obtain solutions for the first and second moments of the waiting time. We then go further to obtain the fidelity distribution of the resulting quantum states, which encapsulates information about their ages. As an application of these results, we demonstrate how they can be used to study sufficient parameter regimes for carrying out Verifiable Blind Quantum Computation in the presence of imperfect entangled links and memory decoherence. We present a method that, in the presence of an arbitrary function capturing the trade-off between the rate and fidelity of an entangled link, finds the optimal choice for the window size which minimises the expected time taken to carry out one component round of the protocol. In this way, we connect parameters corresponding to the underlying network architecture to the performance of the VBQC application. |
Wednesday, March 8, 2023 3:36PM - 3:48PM |
Q70.00004: Requirements for processing-node quantum repeaters on a real-world fiber grid Francisco Ferreira da Silva, Stephanie Wehner, Guus Avis We numerically study the distribution of entanglement on a real-world fiber grid connecting the German cities of Bonn and Berlin realized with a chain of processing-node quantum repeaters spanning roughly 900 kilometers. We determine minimal hardware requirements for two quantum network applications, blind quantum computation and quantum key distribution starting from currently realized group-IV color center and trapped ion parameters. We investigate how the minimal hardware requirements depend on the currently achievable parameters, target application as well as on characteristics of the repeater chain such as number of nodes and their placement. We implement our repeater chain simulations using the discrete-event quantum network simulator NetSquid, which allows us to accurately track time-dependent noise and implement repeater chain protocols with cut-offs, including the required classical communication. We find minimal hardware requirements by solving an optimization problem using genetic algorithms on a high-performance-computing cluster. Our work sheds light on the path towards scaling quantum repeaters to distribute high-quality entanglement over hundreds of kilometers. |
Wednesday, March 8, 2023 3:48PM - 4:00PM |
Q70.00005: Using Nonclassical Resources to Strengthen Two-Party Zero-Communication Reductions Sarah M Hagen, Eric A Chitambar In this work, we investigate the quantum advantage gained by adapting the recently introduced classical zero-communication reduction (ZCR) framework to non-classical resources (“Zero-communication reductions”, Narayanan et al., Theory of Cryptography, 2020) . This problem may be described as a trusted delegated computation in which two parties aim to compute a function f without communicating, interacting only with a third party that arbitrates a resource and computes a different (predicate) function - this effects a reduction from f to the predicate. We strengthen the ZCR using a non-signaling (NS) resource, a relaxation of shared entanglement. The goal is to guarantee the privacy of the computation. By modeling this reduction as a linear program, we show that replacing the classical resource with the NS resource yields improved feasibility results. Notably a reduction from AND to XOR, insecure in the classical setting, may be achieved securely using a NS resource in both the one-output and two-output setting, in which both parties obtain the output of the function. |
Wednesday, March 8, 2023 4:00PM - 4:12PM |
Q70.00006: Optimal entanglement distribution policies in homogeneous repeater chains with cutoffs Álvaro G Iñesta, Gayane Vardoyan, Lara Scavuzzo, Stephanie Wehner We study the limits of entanglement distribution using a chain of quantum repeaters that have memory and perform entanglement swapping to connect short-distance into long-distance entanglement. We take time to be slotted: each node can perform heralded entanglement generation with its neighbor(s) and an entanglement swapping measurement per time slot. Moreover, qubits stored at the repeaters are subjected to a maximum storage time, known as cutoff – used to ensure a minimum fidelity of the resulting end-to-end states. |
Wednesday, March 8, 2023 4:12PM - 4:24PM |
Q70.00007: Effect of Asymmetry on the Performance of Atomic Ensemble Based Repeater Protocols Hana Jirovská, Stephanie Wehner, David Maier Long-distance entanglement distribution is a formidable technological challenge. Quantum repeaters can in theory be used to enable this goal, with much work having been done on the effect of hardware imperfections on their performance. However, these investigations were mostly performed under the assumption of symmetric placement of quantum repeaters and heralding stations, while it is likely that real-world deployment of quantum repeaters will make use of existing fiber networks. This inevitably implies asymmetric node placement. Here, we numerically investigate how asymmetric placement of nodes affects the performance of atomic-ensemble elementary-link and single-repeater setups, building on existing simulations based on the discrete-event quantum-network simulator NetSquid. We find that the secret key rate achievable by an elementary link performing entanglement-based quantum key distribution decreases as the degree of asymmetry increases. Furthermore, we find that this effect can be mitigated by individually optimizing each of the photon sources used for elementary-link generation and we introduce a heuristic that allows us to reduce the search space over which this optimization is performed. We believe that this work constitutes a valuable stepping stone towards realistic investigations on the effect of asymmetry on the feasibility of long-distance entanglement distribution. |
Wednesday, March 8, 2023 4:24PM - 4:36PM Author not Attending |
Q70.00008: Secure multi-party quantum computation protocol built on top of the triply-even quantum error-correcting codes Petr A Mishchenko, Keita Xagawa Secure multi-party quantum computation (MPQC) protocol is a cryptographic task which enables error-free distributed quantum computation to a group of $n$ mutually distrustful quantum nodes even when some of the quantum nodes do not follow the instructions of the protocol honestly [1]. In this talk we describe MPQC protocol which adopts unconventional triply-even Calderbank-Shor-Steane (CSS) quantum error-correcting codes (QECCs) [2-5]. Our decision allows us to avoid previously indispensable but ambiguous procedure of the “magic” state verification present in the preceding MPQC protocol built on top of the self-dual CSS QECCs [6]. Besides, since every extra qubit reduces the credibility of physical devices, our suggestion makes the MPQC protocol more accessible for the near-future technology by reducing the number of necessary qubits per quantum node from $n^2 + 4n$ to $n^2 + 3n$ [7]. |
Wednesday, March 8, 2023 4:36PM - 4:48PM |
Q70.00009: Symmetry Protection of Measurement-based Teleportation in Ising Graphs Zhangjie Qin, Vito W Scarola, Robert Raussendorf, Eran Sela, Daniel Azses Symmetry protected topological (SPT) phases can be identified from degeneracies in their entanglement spectrum and show stability to certain unitary perturbations thanks to string symmetries. Graph state chains have been shown, incidentally, to possess such SPT order which, in turn, protects measurement-based teleportation along the chain. We discuss a new class of SPT states which we call Ising graphs. We define a hierarchy to construct stabilizers that establish multiple string symmetries in Ising graphs beyond just chain geometries. Using our approach, protection against Ising-type unitary perturbations can be engineered within the Ising graph. We find that Ising graphs can be constructed to host redundancy of the degeneracy in the entanglement spectrum which then protects measurement-based teleportation by allowing information copies to move along various paths within the graph. We perform experiments on a real quantum device to demonstrate such multi-path stability. Our analysis of the entanglement spectrum of certain Ising graphs provides insight into encoding SPT order into higher dimensional quantum states. |
Wednesday, March 8, 2023 4:48PM - 5:00PM |
Q70.00010: Bounds on Bipartite Entanglement Distribution Rates for Discrete and Continuous Variable Quantum Switches Ian J Tillman, Thirupathaiah Vasantam, Saikat Guha, Kaushik P Seshadreesan Many potential applications of the quantum internet will require quantum switches that can connect many end users and act as a quantum repeater to extend the range at which we can distribute entanglement. Different applications may require different physical encodings of quantum information, all of which can be described as either a discrete variable encoding or a continuous variable encoding. Here we analyze models for quantum repeating switches that take into account request rates for different types of end-to-end entanglements for either discrete or continuous quantum encodings. We present a method for finding analytical bounds on the supportable request rates, i.e., rates for which request queues are stable, meaning the average waiting times for requests are finite. With the use of a throughput optimal Max-Weight scheduling policy we simulate the switches acting in stable and unstable modes of operation that support the analytical findings. |
Wednesday, March 8, 2023 5:00PM - 5:12PM |
Q70.00011: Memory Decoherence-Aware Entanglement Purification in Quantum Communication Networks Allen Zang, Xinan Chen, Alexander Kolar, Joaquin F Chung Miranda, Martin Suchara, Rajkumar Kettimuthu, Eric A Chitambar Distributing entanglement in quantum repeater networks with sufficiently high fidelity is required to support applications such as quantum teleportation, distributed quantum computation, or quantum sensing. Early realizations of quantum repeater network architectures are not likely to support quantum error correction, and the speed of entanglement distribution will be limited by classical communication latency. Fidelity of distributed entanglement will be therefore susceptible to degradation due to memory decoherence. To address this problem, some previous studies considered re-initializing quantum memories after a predetermined amount of time. However, with this approach it is only possible to distribute entanglement with fidelity below the fidelity of newly generated entangled states. This work uses analytical tools and simulation to evaluate the performance of entanglement purification in realistic scenarios. We consider entanglement purification based on recurrence protocols for non-independent and identically distributed state ensembles, and explore purification strategies that depend on the available quantum memory capacity and state fidelity. In this talk we present our theory and simulation results, for instance the potential fidelity advantage of wait-till-the-end strategy over purify-immediately strategy. |
Wednesday, March 8, 2023 5:12PM - 5:24PM |
Q70.00012: Quantum Steganography in an Optical Channel Bruno Avritzer, Todd A Brun Steganography is an alterantive to cryptography, where information is protected by secrecy — being disguised as innocent communications or noise — rather than being scrambled. In this work we develop schemes for steganographic communication using Fock and coherent states in optical channels based on disguising the communications as thermal noise. We derive bounds on their efficiency in the case of an all-powerful eavesdropper, and provide explicit methods of encoding and error correction for the noiseless channel case. |
Wednesday, March 8, 2023 5:24PM - 5:36PM |
Q70.00013: Entanglement Distribution over Two-Sided Noisy Quantum Channels Xinan Chen, Eric A Chitambar We theoretically investigate the entanglement distribution process where both subsystems of the bipartite entangled state undergo noisy evolutions described by quantum channels. After the noisy evolutions, we assume that the two participating parties can perform local operations and classical communication to distill high-fidelity maximally entangled states from the noisy output of the quantum channels. In our work, we will focus on two particular cases where both channels are dephasing channels and where both channels are amplitude-damping channels. In both cases, we begin with the simpler regime where each channel is used twice and study the best achievable fidelity. Then we move on to the asymptotic regime, where each channel is used infinitely many times, and study the asymptotic rate at which maximally entangled states can be established per channel use. In both regimes, we find the interesting phenomenon that using an initial state that is entangled across different channel uses is more advantageous than using independent copies of maximally entangled states. |
Wednesday, March 8, 2023 5:36PM - 5:48PM |
Q70.00014: Multipartite Nonlocality in Clifford Networks Amanda Gatto Lamas, Eric A Chitambar The rapid development of the theory and experimental realization of quantum networks makes it essential to characterize the features and limitations of different kinds of networks. The limitations of Clifford quantum information processing have been explored both in the sense of classical simulability under the light of the Gottesman-Knill theorem, and of the emergence of quantum nonlocality in specific scenarios. However, it has remained relatively unexplored in a quantum network setting - that is, with limited connectivity and no communication of global information. |
Wednesday, March 8, 2023 5:48PM - 6:00PM |
Q70.00015: Quantifying the performance of approximate teleportation and quantum error correction via symmetric two-PPT-extendibility Vishal Singh, Mark M Wilde, Tharon Holdsworth The ideal realization of quantum teleportation relies on having access to a maximally entangled state; however, in practice, such an ideal state is typically not available and one can instead only realize an approximate teleportation. With this in mind, we present a method to quantify the performance of approximate teleportation when using an arbitrary resource state. More specifically, after framing the task of approximate teleportation as an optimization of a simulation error over one-way local operations and classical communication (LOCC) channels, we establish a semi-definite relaxation of this optimization task by instead optimizing over the larger set of two-PPT-extendible channels. The main analytical calculations in our paper consist of exploiting the unitary covariance symmetry of the identity channel to establish a significant reduction of the computational cost of this latter optimization. Next, by exploiting known connections between approximate teleportation and quantum error correction, we also apply these concepts to establish bounds on the performance of approximate quantum error correction over a given quantum channel. Finally, we evaluate our bounds for various examples of resource states and channels. |
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