Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session F27: Physical Implementations of Qubits 
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Sponsoring Units: GQI Chair: John Preskill, California Institute of Technology Room: 329 
Tuesday, March 19, 2013 8:00AM  8:12AM 
F27.00001: Majorana fermions in 1D superconducting wires subject to disorder and other spatial inhomogeneities Wade DeGottardi, Diptiman Sen, Smitha Vishveshwara We present a systematic study of the role that disordered and quasiperiodic potentials play in the topology of 1D pwave superconducting systems characterized by boundary Majorana modes. We forge a connection between Majorana wave functions and the localization properties of the corresponding normal state system (i.e, one which, though otherwise identical, lacks superconducting order). This enables the leveraging of the vast body of literature on Anderson localization to extensively map the topological phase diagram in superconducting wires. We find that the phase boundary is extremely sensitive to the detailed form of the potential. Our analysis provides a mapping between the limits of weak and strong disorder; in some cases, we are able to find the full phase boundary analytically. A noteworthy discovery is a telltale singularity in the phase boundary at the point corresponding to the quantum Ising model, a feature which offers a window into the physics of Majorana fermions. Our results can be directly applied to a spin1/2 XY chain in a transverse magnetic field which is quasiperiodic or disordered. [Preview Abstract] 
Tuesday, March 19, 2013 8:12AM  8:24AM 
F27.00002: Universal transport signatures of Majorana fermions in superconductorLuttinger liquid junctions Jason Alicea, Lukasz Fidkowski, Netanel Lindner, Roman Lutchyn, Matthew Fisher One of the most promising proposals for engineering Majorana fermions employs a spinorbitcoupled nanowire proximate to an swave superconductor. When only part of the wire's length contacts to the superconductor, the remaining conducting portion serves as a natural lead that can be used to probe these Majorana modes via tunneling. The enhanced role of interactions in 1D dictates that this configuration should be viewed as a superconductorLuttinger liquid junction. We demonstrate that lowenergy transport in such junctions is \emph{universal}, and governed by fixed points describing either perfect normal reflection or perfect Andreev reflection. In addition to capturing (in some instances) the familiar Majoranamediated zerobias anomaly in a new framework, we show that interactions yield dramatic consequences in certain regimes. Implications for conductance and local density of states measurements will be discussed. [Preview Abstract] 
Tuesday, March 19, 2013 8:24AM  8:36AM 
F27.00003: Coherent oscillations between single fluxonium qubit and Majorana fermion qubit ChangYu Hou, David Pekker, Vladimir Manucharyan, Eugene Demler We propose a hybrid device that couples a Majorana qubit to a superconducting fluxonium qubit. The devices consists of a conventional swave superconductor (e.g. Nb) ring interrupted by a narrow gap and a section of topological 1D wire bridging across the gap. Such topological 1D wire can be realized by using a semiconducting nanowire with strong spin orbit scattering (e.g. InSb) subjected by magnetic field. The nanowire hosts a topological qubit formed by four Majorana fermions and acts as a Josephson junction that completes the superconducting ring and makes a fluxonium qubit. As the currentphase relation of the Josephson junction is controlled by the state of the Majorana qubit, the fluxonium and Majorana qubit are naturally coupled. We demonstrate how this coupling can be exploited to construct two qubit operations. Remarkably, quantum information can be transformed between two distinct types of qubits solely using wellcontrolled operations on the fluxonium qubit. [Preview Abstract] 
Tuesday, March 19, 2013 8:36AM  8:48AM 
F27.00004: Majorana Zero Modes in Semiconductor Nanowires in Contact with HigherTc Superconductors Younghyun Kim, Jennifer Cano, Chetan Nayak We present the prospects for stabilizing Majorana zero modes in semiconductor nanowires that are proximitycoupled to highertemperature superconductors. We begin with the case of iron pnictides which, though they are $s$wave superconductors, are believed to have superconducting gaps that change sign. We then consider the case of cuprate superconductors. We show that a nanowire on a steplike surface, especially in an orthorhombic material such as YBCO, can support Majorana zero modes at an elevated temperature. [Preview Abstract] 
Tuesday, March 19, 2013 8:48AM  9:00AM 
F27.00005: Coherent population trapping of hyperfinecoupled single spins in diamond Andrew Golter, Nima Dinyari, Hailin Wang Coherent population trapping (CPT) provides a highly sensitive means for probing the energy level structure of an atomic system. For diamond nitrogen vacancy (NV) centers, this technique offers an alternative to the standard opticallydetected magnetic resonance (ODMR) for measuring the hyperfine structure of the electronic ground states. Here, we report an experimental study using CPT to probe the hyperfine splitting of these states as well as the AutlerTownes effect induced by a strong resonant microwave field. This nuclear spin dependent CPT was also employed along with other coherent spin operations for the initialization and manipulation of hyperfinecoupled nuclear spins. In addition, the use of CPT process to incorporate NV centers into a cavity QED system will be discussed. [Preview Abstract] 
Tuesday, March 19, 2013 9:00AM  9:12AM 
F27.00006: Phonon sideband studies of the spintriplet optical transition in diamond nitrogenvacancy centers Audrius Alkauskas, David M. Toyli, Bob B. Buckley, David D. Awschalom, Chris G. Van de Walle In the past decade, the nitrogenvacancy center in diamond has emerged as a promising solidstate system for quantuminformation processing, and also for nanoscale magnetic, electric, and thermal sensing. All of these applications are partly enabled because the spin of the center can be measured through photoluminescence. This calls for a deeper understanding of the photoluminescence spectrum, in particular its phonon sideband. In this work we study the coupling of lattice vibrations to the triplet ($^3$E$\rightarrow$$^3$A$_2$) optical transition from firstprinciples electronic structure calculations. Our formulation includes both quasilocalized and bulk phonons, and leads to an excellent agreement of the calculated and the measured photoluminescence lineshape. This good agreement enables the application of the developed methodology to other defects in semiconductors that are currently being investigated as viable quantum bits. [Preview Abstract] 
Tuesday, March 19, 2013 9:12AM  9:24AM 
F27.00007: MeasurementOnly Topological Quantum Computation via Tunable Interactions Parsa Bonderson I examine, in general, how tunable interactions may be used to perform anyonic teleportation and generate braiding transformations for nonAbelian anyons. I explain how these methods are encompassed by the ``measurementonly'' approach to topological quantum computation. The physically most relevant example of Ising anyons or Majorana zeromodes is considered in detail, particularly in the context of Majorana nanowires. [Preview Abstract] 
Tuesday, March 19, 2013 9:24AM  9:36AM 
F27.00008: Quantum information processing using quasiclassical electromagnetic interactions between qubits and electrical resonators Andrew Kerman Electrical resonators are widely used in quantum information processing with any qubits that are manipulated via electromagnetic interactions. In most cases they are engineered to interact with qubits via real or virtual exchange of (typically microwave) photons, and the resonator must therefore have both a high quality factor and strong quantum fluctuations, corresponding to the strongcoupling limit of cavity QED. Although great strides in the control of quantum information have been made using this socalled ``circuit QED'' architecture, it also comes with some important disadvantages. In this talk, we discuss a new paradigm for coupling qubits electromagnetically via resonators, in which the qubits do not exchange photons with the resonator, but instead exert quasiclassical, effective ``forces" on it. We show how this type of interaction is similar to that induced between the internal state of a trapped atomic ion and its centerofmass motion by the photon recoil momentum, and that the resulting entangling operations are insensitive both to the state of the resonator and to its quality factor. The methods we describe are applicable to a variety of qubitresonator systems, including superconducting and semiconducting solidstate qubits, and trapped molecular ions. [Preview Abstract] 
Tuesday, March 19, 2013 9:36AM  9:48AM 
F27.00009: Generation and characterization of hypercubic cluster states in the optical frequency comb Moran Chen, Pei Wang, Nicolas Menicucci, Olivier Pfister We report on experimental progress toward generating and characterizing a very large quantum wire cluster state of the continuous electromagnetic variables (``Qmodes'') in the optical frequency comb of an optical parametric oscillator (OPO). We also present a proposal for creating higherdimensional graph states by entangling the linear cluster states of several OPOs, each OPO adding a dimension to the graph (line, square grid, cube, hypercube). Besides the scalable (in number, size, and dimension) creation of sophisticated quantum graphs over hundreds to thousands of Qmodes, this work also constitutes a considerable experimental simplification of our previous proposal for generating a squaregrid cluster state in a single OPO. [Preview Abstract] 
Tuesday, March 19, 2013 9:48AM  10:00AM 
F27.00010: Entangled Photon Holes Todd Pittman, Junlin Liang, James Franson Entangled photon hole (EPH) states represent a new form of entanglement that is based on the existence of ``missing pairs'' of photons in two optical modes. In contrast to the more familiar photon pairs entangled in polarization or other variables, the entanglement in EPH states arises from the absence of the photon pairs themselves. We will review recent experimental work on the generation of these states, and theoretical work showing that they can be relatively insensitive to loss and amplification noise in certain situations. We will also report on our recent efforts to generate timebin EPH states which have different properties than energytime EPH states. [Preview Abstract] 
Tuesday, March 19, 2013 10:00AM  10:12AM 
F27.00011: Informationefficient phase imaging with heralded single photons Reihaneh Shahrokhshahi, Niranjan Sridhar, Olivier Pfister, Saikat Guha, Jonathan Habif, Aaron Miller, Adriana Lita, Brice Calkins, Thomas Gerritts, Antia LamasLinares, Sae Woo Nam We report progress toward the experimental realization of informationefficient quantum imaging, here at two bits per photon. A heralded singlephoton source ($g^{2}(0)<0.08$) is used as the input to a 4x4 multiport interferometer, compactly implemented using both polarization and spatial degrees of freedom. The interferometer can be used to read out all 4 Hadamard phase codes with a single photon. We investigate the use of cavityenhanced spontaneous parametric downconversion for the coherent source of heralded photons. The photonnumberresolving ability of highquantumefficiency transition edge sensors is used for the heralding and detection. [Preview Abstract] 
Tuesday, March 19, 2013 10:12AM  10:24AM 
F27.00012: A TwoQubit Geometric Phase Gate for Localized Electron Spin Qubits using Cavity Polariton Resonance Shruti Puri, Na Young Kim, Yoshihisa Yamamoto We propose a twoqubit geometric phase gate, in which the interaction between a pair of localized electron spins, is mediated by quantum well microcavity excitonpolaritons. The entanglement between the electrons is a result of their spin dependent Coulomb exchange interaction with the excitonpolaritons. This optical coupling, resembling the electronelectron RudermanKittelKasuyaYosida (RKKY) interactions, offers high speed, high fidelity twoqubit gate operation with moderate cavity quality factor Q. The long ranged interaction by microcavity polaritons (order of micrometers) makes this gate suitable for fault tolerant operations. By the use of electrostatic quantum dots, the errors caused by unwanted excitations to charged excitons or trions are eliminated. The errors due to the finite lifetime of the polaritons can be minimized by optimizing the optical pulse parameters (duration and energy). The proposed design maximizes entanglement and ensures scalability. [Preview Abstract] 
Tuesday, March 19, 2013 10:24AM  10:36AM 
F27.00013: Quantum Computing using Photons Ahmed Elhalawany, Michael Leuenberger In this work, we propose a theoretical model of twoquantum bit gates for quantum computation using the polarization states of two photons in a microcavity. By letting the two photons interact nonresonantly with four quantum dots inside the cavity, we obtain an effective photonphoton interaction which we exploit for the implementation of an universal XOR gate. The twophoton Hamiltonian is written in terms of the photons' total angular momentum operators and their states are written using the Schwinger representation of the total angular momentum. [Preview Abstract] 
Tuesday, March 19, 2013 10:36AM  10:48AM 
F27.00014: Charge pumping by a surface acoustic wave in an undoped quantum well: a potential singlephoton source S.K. Son, Y. Chung, J. Pedros, C.J.B. Ford, C.H.W. Barnes, J.P. Griffiths, G.A.C. Jones, I. Farrer, D.A. Ritchie Singleelectron transfer between distant quantum dots using the potential minima of surface acoustic waves (SAWs) has been demonstrated recently, with possible applications for quantum computation. We have developed a technique to induce electrons and holes in an undoped GaAs/AlGaAs quantum well in different regions of the same device using gates, and to transport a stream of single electrons or holes along a narrow, empty channel using SAWs. The potential has a steep slope at the edges of the inducing gates, but we have modelled the potential profile of the active region to find designs in which the potential slope is shallow enough to allow the SAW potential to drag electrons out of the induced region, towards the region of holes. Recombination of each electron with one of the holes should produce a photon and we are investigating the use of this device as a singlephoton source. If the electrons are spinpolarised then their spins can be detected by measuring the circular polarisation of the photons, and this may be useful for spin readout in a quantum processor, or as part of a quantum repeater in quantum cryptography. [Preview Abstract] 

F27.00015: ABSTRACT WITHDRAWN 
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