Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session L28: Distributed Quantum Computation, Networking and Information Security IFocus

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Sponsoring Units: DQI Chair: Stephanie Wehner, Delft Univ of Tech Room: BCEC 161 
Wednesday, March 6, 2019 11:15AM  11:51AM 
L28.00001: Linking trappedion quantum nodes Invited Speaker: Tracy Northup Future quantum networks offer a promising route to quantumsecure communication, distributed quantum computing, and quantumenhanced sensing. The applications of a given network will depend on the capabilities available at its nodes, which may be as simple as quantum state generation and measurement or as advanced as a universal quantum computer. Here, we focus on quantum nodes based on calcium ions confined in a linear Paul trap, an experimental platform with which highfidelity state preparation, gate operations, and readout have been demonstrated. 
Wednesday, March 6, 2019 11:51AM  12:03PM 
L28.00002: Diamond quantum networks for distributed quantum computation Tim Hugo Taminiau A promising approach for quantum computations is to distribute logical qubits and error correction over a quantum network. This approach is naturally extendable to larger sizes by adding independent modules and enables exploring a large variety of error correction codes over different network topologies, including threedimensional structures and nonnearest neighbor connections. 
Wednesday, March 6, 2019 12:03PM  12:15PM 
L28.00003: Distributed Quantum Computing Architectures Martin Suchara, Yuri Alexeev, Joaquin Chung Miranda, Rajkumar Kettimuthu Despite dramatic improvements in quantum gate fidelities, coherence times and qubit counts, the capabilities of quantum processors will remain modest in the near future. We compare two approaches that use small unreliable quantum processors to solve large computational problems. The first approach uses hybrid quantumclassical architectures where larger quantum circuits are broken into smaller subcircuits that are evaluated separately, either using small quantum processors or a quantum simulator running on a classical supercomputer. The second approach leverages quantum networks to teleport shared qubits between quantum processors. We compare the suitability of these techniques for various quantum circuits, describe optimizations that enable mapping quantum circuits into subcircuits, and compare the hardware requirements of the two approaches. 
Wednesday, March 6, 2019 12:15PM  12:27PM 
L28.00004: Numerical finitekey analysis of quantum key distribution Darius Bunandar, Dirk R. Englund Quantum key distribution (QKD) is still the only quantumresistant method of sending secret information at a distance. However, accurate theoretical analysis of QKD that accounts for device imperfections is usually challenging. To circumvent this problem, we have developed an efficient numerical approach to calculate the secret key rates of any QKD protocol. Our approach takes only a brief description of the protocol and the measurement results as inputs. The method outputs the secret key rates by solving a semidefinite program which includes not only practical device imperfections but also statistical fluctuations typically observed in QKD experiments. 
Wednesday, March 6, 2019 12:27PM  12:39PM 
L28.00005: Distributed Routing in a Quantum Internet Kaushik Chakraborty, Axel Dahlberg, Filip Rozpedek, Stephanie Wehner The aim of Quantum Internet is to enable the transmission of qubits between distant quantum devices, in order to achieve tasks that are impossible using classical information. Due to the losses in communication channel, routers are necessary for long distance quantum communication. In such a network, two distant parties share entanglement using the repeaters and transmit qubits using teleportation. However, due to the technological limitation, establishing long distance entanglement takes time and it increases waiting time. This raises the question whether an advantage can be achieved by distributing entanglement ahead of time. In this article we study distribution of entanglement in advance in a network vs producing it on demand. Here we model this problem as a distributed routing in an undirected simple graph. The nodes and edges in the graph denote the routers and communication links. To share an entangled state, two nodes first find a path in the graph and then use the preshared entanglement to perform entanglement swapping along that path. To find a path in the graph we use greedy location based routing algorithms. We have done a comparative study of the waiting time for all of the models. 
Wednesday, March 6, 2019 12:39PM  12:51PM 
L28.00006: Quantum Network Simulations Joaquin Chung Miranda, Rajkumar Kettimuthu, Martin Suchara, Yuri Alexeev Network simulations are extensively used in the design, operation, and evolution of largescale classical networks. We expect that simulations will also play a significant role in developing and evolving quantum networks. Our work focuses on developing quantum network simulators at various network layers ranging from the physical layer to applications. We envision the need for three simulators. The lowestlayer simulator allows us to study the physics of optical networks; an intermediatelayer simulator studies quantum networking protocols and the classical control network; and the highestlayer one simulates behavior of distributed quantum systems. The lowestlayer simulator uses Monte Carlo methods to evaluate the effects of Pauli errors and investigate the effectiveness of entanglement purification or error correction in the presence of realistic noise. The intermediatelayer simulator uses traditional techniques such as discrete event simulation to investigate scalability of network topologies and ability to communicate between arbitrary pairs of network nodes. Finally, the highestlayer simulator emulates both quantum computing and quantum networking by using HPC. It can be used for testing and developing new distributed quantum algorithms and applications. 
Wednesday, March 6, 2019 12:51PM  1:03PM 
L28.00007: Anonymous transmission in a noisy quantum network using the W state Victoria Lipinska, Gláucia Murta, Stephanie Wehner We consider the task of anonymously transmitting a quantum message in a network. In this task, we are concerned with hiding the identities of the sender and receiver of the message from other nodes of the network. We present a protocol that accomplishes this task using the W state. We analyze its performance in a quantum network where common forms of noise are present, and then compare the performance of our protocol with some of the existing protocols developed for the task of anonymous transmission. We show that, in many regimes, our protocol tolerates more noise and achieves higher fidelities of the transmitted quantum message than the other ones. Furthermore, we demonstrate that our protocol tolerates one nonresponsive node, as opposed to other considered protocols. Finally, we prove the security of our protocol in a semiactive adversary scenario, i.e. when the adversary is active and the source of a quantum state is trusted. 
Wednesday, March 6, 2019 1:03PM  1:15PM 
L28.00008: Towards a multinode network with NV centres in diamond Matteo Pompili, Sophie L. N. Hermans, Hans K.C. Beukers, Romy van Es, Simon Baier, Ronald Hanson Quantum networks are expected to deliver definitive security for communication, blind quantum computation, improved clock synchronization and more exotic applications such as connecting far apart telescopes. A node of such a network must be capable of running small quantum computations, storing quantum information in memory qubits and generate entanglement with neighbouring nodes. 
Wednesday, March 6, 2019 1:15PM  1:27PM 
L28.00009: Cavity enhanced spinphoton interaction for a diamond based quantum network Matthew Weaver, Maximilian Ruf, Santi Sager La Ganga, Suzanne Van Dam, Guus Evers, Martin Eschen, Nick de Jong, Hans van den Berg, Jasper Flipse, Ronald Hanson Fast and efficient entanglement generation is a fundamental building block for proposed long distance quantum networks. Nitrogen vacancy (NV) centers in diamond present a promising platform for such a network, because of their long electron spin coherence times, available nuclear spin registers and near lifetime limited optical properties. However, the small fraction of photons emitted into the zero phonon line has so far limited entanglement generation rates to below 39 Hz. We construct high finesse fiber based cavities with a microns thick diamond membrane and measure the NV cavity interaction. Purcell enhancement of the emission into the zero phonon line and better coupling efficiency could increase entangling rates by two orders of magnitude. Here we report on the latest results towards these goals. 
Wednesday, March 6, 2019 1:27PM  1:39PM 
L28.00010: Impact of qubit connectivity on quantum algorithm performance Adam Holmes, Sonika Johri, Gian Giacomo Guerreschi, Jim Clarke, Anne Matsuura Quantum computing hardware is undergoing rapid development from proofofprinciple devices to scalable machines that could eventually challenge classical supercomputers on specific tasks. On platforms with local connectivity, the transition from one to twodimensional arrays of qubits is seen as a natural technological step to increase the density of computing power and to reduce the routing cost of limited connectivity. Here we map and schedule representative algorithmic workloads  the Quantum Fourier Transform (QFT) relevant to factoring, the Grover diffusion operator relevant to quantum search, and JordanWigner parity rotations relevant to simulations of quantum chemistry and materials science  to qubit arrays with varying connectivity. In particular we investigate the impact of restricting the ideal alltoall connectivity to a square grid, a ladder and a linear array of qubits. Our schedule for the QFT on a ladder results in running time close to that of a system with alltoall connectivity. Our results suggest that some common quantum algorithm primitives can be optimized to have execution times on systems with limited connectivities, such as a ladder and linear array, that are competitive with systems that have alltoall connectivity. 
Wednesday, March 6, 2019 1:39PM  1:51PM 
L28.00011: Timebin and Polarization Superdense Teleportation for Space Applications Joseph Chapman, Trent Graham, Christopher Zeitler, Paul G Kwiat

Wednesday, March 6, 2019 1:51PM  2:03PM 
L28.00012: Simulation of a 1025node quantum repeater chain of NV centres with NetSquid, a new discreteevent quantumnetwork simulator Tim Coopmans, Axel Dahlberg, Matthew Skrzypczyk, Filip Rozpedek, Roeland ter Hoeven, Leon Wubben, Rob Knegjens, Julio de Oliveira Filho, David Elkouss, Stephanie Wehner We simulate quantum repeater chains of up to 1025 nodes holding nitrogenvacancy (NV) centres as quantum processors. We model qubit decoherence, timing and fidelity of both gates and readout according to experimental data. The model also incorporates scheduling operations on the quantum state as imposed by the physics of NV centres. For example, the presence of a single communication qubit, the electron spin, only allows for entanglement generation with one remote node simultaneously. As a consequence of the accurate modelling, the numerical results indicate directions for future hardware development. In particular, we analyse the sensitivity of hardware parameters on the performance of the entire repeater chain. We also perform optimisation over several parameters and configurations, such as the number of NV centres in a single node and the scheduling for entanglement purification steps. 
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