Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session S44: Quantum Architectures and Control |
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Sponsoring Units: GQI Chair: Ryan Babbush, Google Room: 347 |
Thursday, March 17, 2016 11:15AM - 11:27AM |
S44.00001: A universal scheme for indirect quantum control David Layden, Eduardo Martin-Martinez, Achim Kempf The goal of indirect quantum control is to coherently steer a quantum system solely by acting on a quantum actuator to which it is coupled. This approach to quantum control is convenient in many physical settings, as it allows one to avoid direct addressing of the system---and any associated difficulties---altogether. While it is known in principle that control of the actuator typically yields universal control of the system, the practical details of how such indirect control can be achieved are less clear. This deficiency has led to a number of implementation- and model-specific indirect control schemes, in lieu of a general recipe applicable to any physical setting. Here, we present such a recipe, in the form of an open-loop control scheme which implements arbitrary unitary operations on the system by exploiting open dynamics in the actuator. [Preview Abstract] |
Thursday, March 17, 2016 11:27AM - 11:39AM |
S44.00002: Symmetry-protected topologically ordered states for universal quantum computation Hendrik Poulsen Nautrup, Tzu-Chieh Wei Measurement-based quantum computation (MBQC) is a model for quantum information processing utilizing only local measurements on suitably entangled resource states for the implementation of quantum gates. A complete characterization for universal resource states is still missing. It has been shown that symmetry-protected topological order (SPTO) in one dimension can be exploited for the protection of certain quantum gates in MBQC. Here we investigate whether any 2D nontrivial SPTO states can serve as resource for MBQC. In particular, we show that the nontrivial SPTO ground state of the CZX model on the square lattice by Chen et al. [Phys. Rev. B {\bf 84}, 235141 (2011)] can be reduced to a 2D cluster state by local measurement, hence a universal resource state. Such ground states have been generalized to qudits with symmetry action described by three cocycles of a finite group G of order d and shown to exhibit nontrivial SPTO. We also extend these to arbitary lattices and show that the generalized two-dimensional plaquette states on arbitrary lattices exhibit nontrivial SPTO in terms of symmetry fractionalization and that they are universal resource states for quantum computation. SPTO states therefore can provide a new playground for measurement-based quantum computation. [Preview Abstract] |
Thursday, March 17, 2016 11:39AM - 11:51AM |
S44.00003: ABSTRACT WITHDRAWN |
Thursday, March 17, 2016 11:51AM - 12:03PM |
S44.00004: Quantum Ultra-Walks: Walks on a Line with Spatial Disorder Stefan Boettcher, Stefan Falkner We discuss the model of a heterogeneous discrete-time walk on a line with spatial disorder in the form of a set of ultrametric barriers. Simulations show that such an quantum ultra-walk spreads with a walk exponent $d_w$ that ranges from ballistic ($d_w=1$) to complete confinement ($d_w=\infty$) for increasing separation $1\leq1/\epsilon<\infty$ in barrier heights. We develop a formalism by which the classical random walk as well as the quantum walk can be treated in parallel using a coined walk with internal degrees of freedom. For the random walk, this amounts to a $2^{\rm nd}$-order Markov process with a stochastic coin, better know as an (anti-)persistent walk. The exact analysis, based on the real-space renormalization group (RG), reproduces the results of the well-known model\footnote{J.~Phys.~A {\bf 19}(1986)L269} of ``ultradiffusion,'' $d_w=1-\log_2\epsilon$ for $0<\epsilon\leq1/2$ . However, while the evaluation of the RG fixed-points proceeds virtually identical, for the corresponding quantum walk with a unitary coin\footnote{\urllink{Phys.~Rev.~A {\bf 90}(2014)032324, \hfill http://arxiv.org/abs/1311.3369}{http://arxiv.org/abs/1311.3369}} it fails to reproduce the numerical results. A new way to analyze the RG is indicated. [Preview Abstract] |
Thursday, March 17, 2016 12:03PM - 12:15PM |
S44.00005: Quantum walks outside of boolean domain as a gate for one, two, or three qubits. Thomas Cavin, Dmitry Solenov Quantum computing needs entangling quantum gates to perform computation and error correction. We will discuss a novel way to implement quantum gates, such as CNOT, using quantum walks that are directed through a network of states outside of the boolean domain. In such implementations it is important to investigate walks on networks of different connectivities. Specifically, we will discuss solutions to non-symmetric linear chain networks and demonstrate how solutions to more complex networks that have branching, such as cubes, can be expressed in terms of linear chain solutions. We then show examples of implementing single qubit and two-qubit entangling gates. [Preview Abstract] |
Thursday, March 17, 2016 12:15PM - 12:27PM |
S44.00006: Duality quantum computer and the efficient quantum simulations Shijie Wei, guilu long Duality quantum computer is a new kind of quantum computer which is able to perform an arbitrary sum of unitaries, and therefore a general quantum operator. This gives more computational power than a normal quantum computer. All linear bounded operators can be realized in a duality quantum computer, and unitary operators are just the extreme points of the set of generalized quantum gates. Duality quantum computer can provide flexibility and clear physical picture in designing quantum algorithms, serving as a useful bridge between quantum and classical algorithms. In this report, we will firstly briefly review the theory of duality quantum computer. Then we will introduce the application of duality quantum computer in Hamiltonian simulation. We will show that duality quantum computer can simulate quantum systems more efficiently than ordinary quantum computer by providing descriptions of the recent efficient quantum simulation algorithms. [Preview Abstract] |
Thursday, March 17, 2016 12:27PM - 12:39PM |
S44.00007: Optimized probabilistic quantum processors: A unified geometric approach$\backslash $kerning1 Janos Bergou, Emilio Bagan, Edgar Feldman Using probabilistic [1] and deterministic quantum cloning [2], and quantum state separation [3] as illustrative examples we develop a complete geometric solution for finding their optimal success probabilities. The method is related to the approach that we introduced earlier for the unambiguous discrimination of more than two states [4]. In some cases the method delivers analytical results, in others it leads to intuitive and straightforward numerical solutions. We also present implementations of the schemes based on linear optics employing few-photon interferometry.$\backslash $pard[1] V. Yerokhin, A. Shehu, E. Feldman, E. Bagan, and J. Bergou, Probabilistically perfect cloning, submitted to PRL (2015).2] V. Yerokhin, A. Shehu, E. Bagan, E. Feldman, and J. Bergou, Approximate probabilistic cloning, in preparation.3] V. Yerokhin, A. Shehu, E. Feldman, E. Bagan, and J. Bergou, A geometric approach to state separation, submitted to NJP (2015).$\backslash $pard[4] J. Bergou, U. Futschik, and E. Feldman, Optimal unambiguous discrimination of pure quantum states, Phys. Rev. Lett. \textbf{108}, 250502 (2012). [Preview Abstract] |
Thursday, March 17, 2016 12:39PM - 12:51PM |
S44.00008: Three step implementation of any unitary matrix with complete graph of n qubits Amara Katabarwa, Michael Geller The use of programmable array of superconducting qubits for general purpose quantum computation has been recently proposed, and applications to amplitude amplification, phase estimation and simulation of realistic molecular collisions. This Single Excitation Subspace (SES) approach does not require error correction and is practical now. We show that any element in the unitary group U(n) can be generated in three steps, for any n. This allows for implementation of highly complex operations in constant time. [Preview Abstract] |
Thursday, March 17, 2016 12:51PM - 1:03PM |
S44.00009: Recursive linear optical networks for realizing quantum algorithms Gelo Noel Tabia Linear optics has played a leading role in the development of practical quantum technologies. In recent years, advances in integrated quantum photonics have significantly improved the functionality and scalability of linear optical devices [1]. In this talk, I present recursive schemes for implementing quantum Fourier transforms and inversion about the mean in Grover's algorithm with photonic integrated circuits [2]. By recursive, I mean that two copies of a $d$-dimensional unitary operation is used to build the corresponding unitary operation on $2d$ modes. The linear optical networks operate on path-encoded qudits and realize $d$-dimensional unitary operations using $O(d^2)$ elements. To demonstrate that the recursive circuits are viable in practice, I conducted simulations of proof-of-principle experiments using a fabrication model of realistic errors in silicon-based photonic integrated devices. The results indicate high-fidelity performance in the circuits for 2-qubit and 3-qubit quantum Fourier transforms, and for quantum search on 4-item and 8-item databases. Ref: [1] G. D. Marshall, et al., Opt. Express 17, 12546 (2009); [2] G. N. M. Tabia, arXiv:1509.04246 (2015). [Preview Abstract] |
Thursday, March 17, 2016 1:03PM - 1:15PM |
S44.00010: Controlling Quantum Transport with a Programmable Nanophotonic Processor Nicholas Harris, Gregory Steinbrecher, Jacob Mower, Yoav Lihini, Mihika Prabhu, Tom Baehr-Jones, Michael Hochberg, Seth Lloyd, Dirk Englund Recent experimental and theoretical work has revealed emergent, counter-intuitive quantum transport effects in a range of physical medial including solid-state and biological systems. Photonic integrated circuits are promising platforms for studying such effects. A central goal in for photonic quantum transport simulators has been the ability to rapidly control all parameters of the transport problem. Here, we present a large-scale programmable nanophotonic processor composed of 56 Mach-Zehnder interferometers that enables control over modal couplings and differential phases between modes---enabling observations of Anderson localization, environment-assisted quantum transport, ballistic transport, and a number of intermediate quantum transport regimes. Rapid programmability enables tens of thousands of realizations of disordered and noisy systems. In addition, low loss makes this nanophotonic processor a promising platform for many-boson quantum simulation experiments. [Preview Abstract] |
Thursday, March 17, 2016 1:15PM - 1:27PM |
S44.00011: Universal Linear Optics: An implementation of Boson Sampling on a Fully Reconfigurable Circuit Christopher Harrold, Jacques Carolan, Chris Sparrow, Nicholas J. Russell, Joshua W. Silverstone, Graham D. Marshall, Mark G. Thompson, Jonathan C.F. Matthews, Jeremy L. O'Brien, Anthony Laing, Enrique Martín-López, Peter J. Shadbolt, Nobuyuki Matsuda, Manabu Oguma, Mikitaka Itoh, Toshikazu Hashimoto Linear optics has paved the way for fundamental tests in quantum mechanics and has gone on to enable a broad range of quantum information processing applications for quantum technologies. We demonstrate an integrated photonics processor that is universal for linear optics. The device is a silica-on-silicon planar waveguide circuit (PLC) comprising a cascade of 15 Mach Zehnder interferometers, with 30 directional couplers and 30 tunable thermo-optic phase shifters which are electrically interfaced for the arbitrary setting of a phase. We input ensembles of up to six photons, and monitor the output with a 12-single-photon detector system. The calibrated device is capable of implementing any linear optical protocol. This enables the implementation of new quantum information processing tasks in seconds, which would have previously taken months to realise. We demonstrate 100 instances of the boson sampling problem with verification tests, and six-dimensional complex Hadamards. [Preview Abstract] |
Thursday, March 17, 2016 1:27PM - 1:39PM |
S44.00012: Universal Linear Optics: A Testbed for Optical Quantum Logic Chris Sparrow, Jacques Carolan, Christopher Harrold, Nicholas Russell, Graham Marshall, Joshua Silverstone, Mark Thompson, Jonathan Matthews, Jeremy O'Brien, Anthony Laing, Enrique Martin-Lopez, Peter Shadbolt, Nobuyuki Matsuda, Manabu Oguma, Mikitaka Itoh, Toshikazu Hashimoto Linear optics is a promising platform for scalable quantum information processing. We demonstrate a single reprogrammable optical circuit that is sufficient to implement all possible linear optical protocols up the size of the circuit [Carolan et al., Science, 349, (2015)]. The system is an ideal testbed for rapidly prototyping new linear optical quantum gates, and testing known protocols in experimentally realistic scenarios. We use the device to perform a series of postselected and heralded quantum logic gates including a new scheme for heralded bell state generation, a key primitive in measurement-based linear optical quantum computation. We propose and demonstrate techniques for efficiently and accurately characterising and verifying these gates’ operation. The ability to rapidly reprogram linear optical devices promises to replace a multitude of existing and future prototype systems, pointing the way to applications across quantum technologies. [Preview Abstract] |
Thursday, March 17, 2016 1:39PM - 1:51PM |
S44.00013: Entanglement Dynamics in Heisenberg spin systems coupled to a dissipative environment Gehad Sadiek, Samaher Almalki Heisenberg Spin chains and lattices have been intensively used to represent many of the physical systems that are considered as promising candidates for quantum computing and quantum information processing. The main obstacle toward realizing the ultimate goals in these fields is decoherence caused by the surrounding dissipative and thermal environments. We are studying spin relaxation and entanglement dynamics in one and two-dimensional XYZ Heisenberg spin systems under coupling with a dissipative Lindblad environment at finite temperature. We investigate the effect of the anisotropy of the coupling between the spins on the asymptotic steady state of the system and the spin relaxation rates at different temperatures of the environment. We demonstrate the role played by the initial system setup on the entanglement and spin dynamics and steady state properties. Also we examine the effect of the long range interaction between the spins on the asymptotic behavior of the system. [Preview Abstract] |
Thursday, March 17, 2016 1:51PM - 2:03PM |
S44.00014: Geometrical, response, and gap properties of Lindbladians Victor V. Albert, Barry Bradlyn, Martin Fraas, Liang Jiang We study Lindbladians admitting multi-dimensional steady-state subspaces (SSS) which can be used to store, protect, and process quantum information. We derive an analytical formula for the left eigenmatrices of such Lindbladians corresponding to purely imaginary eigenvalues. This formula resolves how Lindbladian evolution affects perturbative response and geometrical features of the SSS and allows us to generalize recent work to all types of SSS. We show that Hamiltonian and certain jump operator perturbations induce, to first order, exclusively unitary evolution on the SSS. Similarly, the holonomy (generalization of geometric phase) induced on the SSS after adiabatic traversal of a closed path in parameter space is unitary. We derive a new Riemannian metric tensor in parameter space induced by one type of SSS, generalizing the Fubini-Study metric to Lindbladians possessing one or more mixed steady states. We derive a Kubo formula governing linear response of the SSS to Hamiltonian perturbations. Finally, we show that the energy scale governing leakage out of the SSS is different from the conventional Lindbladian dissipative gap. [Preview Abstract] |
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