Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session V40: Focus Session: Linear Optics Quantum Computation |
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Sponsoring Units: TGQI DCMP Chair: Jonathan Dowling, Louisiana State University Room: Baltimore Convention Center 343 |
Thursday, March 16, 2006 11:15AM - 11:27AM |
V40.00001: High-fidelity linear optical quantum computing with polarization encoding Federico Spedalieri, Hwang Lee, Jonathan Dowling We show that the KLM scheme [Knill, Laflamme and Milburn, Nature {\bf 409}, 46] can be implemented using polarization encoding, thus reducing the number of path modes required by half. One of the main advantages of this new implementation is that it naturally incorporates a loss detection mechanism that makes the probability of a gate introducing a non-detected error, when non-ideal detectors are considered, dependent only on the detector dark-count rate and independent of its efficiency. Since very low dark-count rate detectors are currently available, a high-fidelity gate (probability of error of order $10^{-6}$ conditional on the gate being successful) can be implemented using polarization encoding. The detector efficiency determines the overall success probability of the gate but does not affect its fidelity. This can be applied to the efficient construction of optical cluster states with very high fidelity for quantum computing. [Preview Abstract] |
Thursday, March 16, 2006 11:27AM - 11:39AM |
V40.00002: Single Photon Source Using Chiral Nematic Liquid Crystal Ganesh Selvaraj, Anand Jha, Pavel Lougovski, Marian Florescu, Robert Boyd, Jonathan Dowling With the development of Linear Optics Quantum Computing, a demand for a good single photon source has increased. Here we describe how a cholesteric liquid crystal can be used as a photonic band-gap material to design a single-photon source.We have a dipole embedded in a liquid crystal for which we find the spontaneous emission rate. We calculate the band structureof the cholesteric liquid crystal using the eigenfuncton expansion method and ultimately compute the density of modes. We also determine the field of the dipole embedded inside the cholesteric liquid crystal using the Green's function method from which we determine the spontaneous emmission rate. [Preview Abstract] |
Thursday, March 16, 2006 11:39AM - 11:51AM |
V40.00003: How to construct a Universal Linear Optical State Generator? Pavel Lougovski, Hwang Lee, Jonathan Dowling We consider all optical realization of a universal quantum state generator utilizing projective photon measurements to create an effective non-linearity. Specifically we are interested in finding a set of unitary optical devices required in order to generate a given quantum state for a given input and a projective measurement. We illustrate the formalism for a case of multi-photon path entangled states (N00N states). We conjecture an existence of necessary criteria connecting a size of a N00N state to a number of input modes of a generator. [Preview Abstract] |
Thursday, March 16, 2006 11:51AM - 12:27PM |
V40.00004: Towards one-way quantum computation with realistic devices Invited Speaker: The one-way model seems particularly suited to certain proposed architectures for quantum computation, particularly those involving non-deterministic quantum gates. This talk will focus on strategies for dealing with faulty devices in the one-way model, particularly within the framework of linear optical quantum computation, although the results have more general significance. Special mention will made of strategies for dealing with faulty single photon sources and detectors, which are the primary experimental challenge for many proposed implementations of optical quantum computation. [Preview Abstract] |
Thursday, March 16, 2006 12:27PM - 12:39PM |
V40.00005: Single-photon sources for linear optics quantum computation Todd Pittman, Bryan Jacobs, James Franson Although single-photon sources have recently been realized in a number of physical systems, only of few of them have experimentally demonstrated the types of properties required for linear optics quantum computing. In this talk, we review these requirements, and discuss the technical and fundamental challenges in meeting them. We will focus on a periodic source in which single-photons heralded from parametric down-conversion pairs are trapped and released from a storage loop. [Preview Abstract] |
Thursday, March 16, 2006 12:39PM - 12:51PM |
V40.00006: Optical Switches for Quantum Information Processing Bryan Jacobs, Todd Pittman, James Franson Many of the basic components required for optical quantum computing and quantum communications have recently been demonstrated, including: single photon sources, quantum memories, logic operations, and photon number resolving detectors. Although the results of these proof-of-concept demonstrations are encouraging, errors in the current devices limit the range of applications to relatively small quantum circuits. The majority of the errors in the current devices originates from photon loss and decoherence in the switching elements. The single-photon nature of the signal, when coupled with quantum coherence requirements, limits the feasibility of using standard telecom switches in these applications. Here we discuss our recent work toward the development of optical switches specifically designed to accommodate the characteristics of photonic qubits. [Preview Abstract] |
Thursday, March 16, 2006 12:51PM - 1:03PM |
V40.00007: Entangled Photon Holes James Franson The probabilistic failure events of linear optics logic gates can be suppressed using the quantum Zeno effect enforced by strong two-photon absorption [1]. This would allow deterministic logic operations as a possible alternative to the use of cluster states. We have recently shown, however, that the rate of two-photon absorption can be substantially reduced by the generation of entangled photon holes that are analogous to the holes of semiconductor theory [2]. This reduction in the two-photon absorption rate is inconsistent with classical or semiclassical theory, and the entangled photon holes can violate Bell's inequality as well. As a practical matter, these difficulties can be avoided if the photons travel in opposite directions, in which case the entangled photon holes propagate away from each. The theory of entangled photon holes and their implications for the design of Zeno gates will be discussed. \begin{enumerate} \item J.D. Franson, B.C. Jacobs, and T.B. Pittman, Phys. Rev. A \textbf{70}, 062302 (2004). \item J.D. Franson, submitted to Phys. Rev. Lett. (quant-ph/0510175). \end{enumerate} [Preview Abstract] |
Thursday, March 16, 2006 1:03PM - 1:15PM |
V40.00008: Creating single time-bin entangled photon pairs Christoph Simon, Jean-Philippe Poizat When a single emitter is excited by two phase-coherent pulses with a time delay, each of the pulses can lead to the emission of a photon pair, thus creating a ``time-bin entangled'' state. Double pair emission can be avoided by initially preparing the emitter in a metastable state. We show how photons from separate emissions can be made indistinguishable, permitting their use for multi-photon interference. Possible realizations with single atoms or ions and with quantum dots are discussed. The method might also allow the direct creation of {\$}n{\$}-photon entangled states (n$>$2). [Preview Abstract] |
Thursday, March 16, 2006 1:15PM - 1:27PM |
V40.00009: Towards a Quantum Memory for Photons in Erbium Doped Materials Sara Hastings-Simon, Matthias Staudt, Barbara Kraus, Wolfgang Tittel, Mikael Afzelius, Nicolas Gisin, Ignacio Cirac, Mattias Nilsson, Stefan Kroll Quantum memories for single photons could play an important role in quantum communication and optical quantum computing. We present a proposal for the efficient storage and recall of photonic time-bin qubits, based on reversible absorption in a controllably broadened homogeneous absorption line. We report on the first experimental steps towards the realization of this quantum memory protocol. In particular, we have measured the homogenous lifetime of the relevant optical transition in erbium doped optical fibers and erbium doped lithium niobate waveguides by spectral hole burning and photon echo. We have also observed the controlled reversible broadening of spectral holes and spectral hole line shifts due to the Stark effect. [Preview Abstract] |
Thursday, March 16, 2006 1:27PM - 1:39PM |
V40.00010: Design of an on demand single photon source using a metal-insulator-semiconductor capacitor structure B.H. Hu, C.H. Yang, M.J. Yang We propose an on-demand single photon source for unconditionally secure quantum cryptography. Similar to a typical metal-insulator-semicondoctor capacitor structure, the main component in the semiconductor is a p-doped quantum well, and the cylindrical gate under consideration is only nanometers in diameter. This MIS system can be biased to inversion, and, due to the small gate area, there are only a few electrons residing in a quantum dot at the onset of inversion. Considering the strong size quantization and large Coulomb energy, the number of electrons can be precisely controlled by the gate voltage. After holding just one electron in the inversion layer, the capacitor is quickly biased back to the flat band condition and the subsequent radiative recombination across the bandgap results in single photon emission. Using GaAs/AlAs as the model system, we present a numerical simulation of three-dimensional band bending and merits of this single photon source. [Preview Abstract] |
Thursday, March 16, 2006 1:39PM - 1:51PM |
V40.00011: Superconducting Bolometric Photon Detectors Using Epitaxial Niobium Thin Films Kevin M. Inderhees, Paul B. Welander, Seongshik Oh, James N. Eckstein Efficient single photon detection is a key part of optical qubit systems. We have made and tested superconducting bolometric photon detectors constructed from high quality epitaxial single crystal niobium films that are very flat. The devices operate at 4.2K and consist of narrow links which are current biased close to their critical current value. Absorption of a photon drives a portion of the device into the normal state, generating an observable voltage signal. The sensitivity is maximized when the link is biased near the critical current. The time averaged output voltage is linearly dependent on the optical power that illuminates the link. In order to optimize detector characteristics, we have studied the effects of changing the film thickness, the device geometry, and adding a protective cap. [Preview Abstract] |
Thursday, March 16, 2006 1:51PM - 2:03PM |
V40.00012: Quantum dots as a source of entangled photon pairs. Mark Stevenson, Robert Young, Paola Atkinson, Ken Cooper, David Ritchie, Andrew Shields Quantum dots are considered an attractive system for applications in quantum communication and quantum logic, confirmed by experimental demonstrations of quantum dot based single photon emission devices. Another key quantum optics resource is the on-demand generation of entangled photon pairs, for which the radiative decay of the biexciton state in a quantum dot has been proposed. The realization of such a device has been prevented due to polarization splitting of the exciton fine structure, caused by anisotropies of various structural parameters of the dot. We present the results of recent experiments that manage the splitting in quantum dots, in order to allow entangled photon emission. We demonstrate that dots with splitting within the homogeneous linewidth can be realized by carefully controlling the thickness of the dot layer. Furthermore, we show that the splitting can be reduced to zero by the application of an in-plane magnetic field. Polarization dependent correlation measurements on these dots will be presented that show characteristic features of entanglement, such as polarization correlation for all linear detection bases, and circular polarization anti-correlation. Our results indicate that for the first time, we have observed triggered entangled photon pair emission from a quantum dot. [Preview Abstract] |
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