Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session S33: Focus Session: Pathway to Practical Quantum Computing |
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Sponsoring Units: GQI DAMOP DCOMP Chair: Daniel Greenberger, City College of New York Room: LACC 511C |
Wednesday, March 23, 2005 2:30PM - 3:06PM |
S33.00001: Measurement and control in quantum information science Invited Speaker: Quantum information science has a broad interface with control theory. In the region of overlap between these two thriving fields, one finds compelling problems ranging from robust and time-optimal control of quantum dynamics to the analysis and design of concatenated coding schemes. In this talk I will begin with a brief overview of recent work on applications of control theory in quantum information science, and then provide a more detailed review of my own group's research on quantum feedback control, quantum state preparation and quantum metrology. [Preview Abstract] |
Wednesday, March 23, 2005 3:06PM - 3:18PM |
S33.00002: Exploiting the Quantum Zeno Effect to Beat Photon Loss in Linear Optical Quantum Information Processors Jonathan Dowling We devise a new technique to enhance transmission of quantum information through linear optical quantum information processors. The idea is based on applying the Quantum Zeno effect to the process of photon absorption. By frequently monitoring the presence of the photon through a QND (quantum non-demolition) measurement the absorption is suppressed. Quantum information is encoded in the polarization degrees of freedom and is therefore not affected by the measurement. Some implementations of the QND measurement are proposed. [Preview Abstract] |
Wednesday, March 23, 2005 3:18PM - 3:30PM |
S33.00003: Control of Anisotropic Spin Exchange in Quantum Dots Dimitrije Stepanenko, Layla Hormozi, Nicholas Bonesteel, Kerwin Foster To first order in spin-orbit coupling, the exchange interaction between spins in coupled quantum dots has the form $J ({\bf S}_1 \cdot {\bf S}_2 + \vec\beta\cdot ({\bf S}_1 \times {\bf S}_2))$. Recently we have shown that the ability to control the Dzyaloshinski-Moriya vector ${\vec\beta}$ is a potentially useful resource for quantum computation.\footnote{D.Stepanenko, N.E.Bonesteel, PRL {\bf 93}, 140501 (2004).} Here we study microscopically the degree of this control for coupled quantum dots in III-V semiconductors. At the level of the Hund-Mulliken (HM) approximation, in which one orbital is kept per dot, spin-orbit coupling enters as a small spin precession during interdot tunneling. $\vec \beta$ is proportional to this precession angle, and its dependence on dot parameters (e.g., interdot distance and dot size) can be strongly enhanced by ferromagnetic direct exchange. We determine the range of effective $\vec \beta$ values in quantum gates produced by pulsing the exchange interaction through numerical integration of the Schr\"odinger equation. Anisotropy in any particular gate is determined by the pulse duration, which is limited by decoherence for slow pulses and adiabaticity for fast pulses. The effects of going beyond the HM approximation, keeping more than one orbital per dot, are also discussed. [Preview Abstract] |
Wednesday, March 23, 2005 3:30PM - 3:42PM |
S33.00004: Conductance peak splitting in coupled Si/SiGe quantum dots L.J. Klein, Srijit Goswami, K.A. Slinker, S.N. Coppersmith, M.A. Eriksson, J.O. Chu, P.M. Mooney The fabrication and electrical characterization of double quantum dots in modulation doped Si/SiGe heterostructure are presented. Trench line defined quantum dots and in plane gates are fabricated by electron beam lithography and reactive ion etching. Low temperature transport measurements (0.2 K) show split Coulomb blockade peaks over a large range of voltages on the side gates. The split conductance peaks indicates a tunnel coupling between the pair of quantum dots and this coupling can be tuned by varying the voltages applied to the gates. The stability plot diagram of the double dot reveals similar conductance diamonds for the individual dots with well resolved excited states. The possible applications of tunnel coupled quantum dots for quantum information processing are discussed. [Preview Abstract] |
Wednesday, March 23, 2005 3:42PM - 4:18PM |
S33.00005: Thresholds for reliable quantum computation Invited Speaker: |
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S33.00006: Entanglement and quantum computational speed-up Guifre Vidal I will discus recent results on the role of entanglement in quantum computation [G. Vidal, Phys. Rev. Lett. 91, 147902 (2003)] and in the efficient numerical simulation of quantum many-body dynamics [G. Vidal, Phys. Rev. Lett. 93, 040502 (2004)]. A pure-state quantum computation can be efficiently simulated with a classical computer provided that only a restricted amount of entanglement is involved. More generally, an upper bound on the computational speed-up offered by a quantum computation can be given in terms of its amount of entanglement. These results follow from an explicit simulation algorithm that can also be applied to efficiently simulate quantum dynamics in one spatial dimension, including spin chain dynamics. [Preview Abstract] |
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