Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session V17: Spin Control and Measurement for Quantum Computation |
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Sponsoring Units: DCMP Chair: Ilya Ponomarev, Naval Research Laboratory Room: LACC 404B |
Thursday, March 24, 2005 11:15AM - 11:27AM |
V17.00001: Spin Charging Sequence in Laterally-Coupled Vertical Triple Quantum Dots Jihan Kim, Dmitriy Melnikov, Jean-Pierre Leburton, Guy Austing We use three-dimensional self-consistent Kohn Sham's Equations coupled with Poisson's Equation to investigate the behavior of a few (N=2,3 and 4) electron system in three co-linear and laterally-coupled quantum dots made with the vertical technology. Under the influence of the central dot gate, we observe the relocation of the ground-state electrons from the central dot to the side dots during both the charging regime ($\Delta$N=1)and the Coulomb blockade regime ($\Delta$N=0). With varying gate voltage, the evolution of the single-particle wavefunctions for N=3 and 4 electrons is also accompanied by changes in the spin states in the case of symmetry breaking in the dot confinement. We discuss various charging scenarios as a function of the different gate bias configurations as well as the possibility to achieve super-exchange with this technolgy. [Preview Abstract] |
Thursday, March 24, 2005 11:27AM - 11:39AM |
V17.00002: Double-dot charge qubit and transport via dissipative cotunneling Mei-Rong Li, Karyn Le Hur We investigate electron cotunneling through an exotic charge qubit composed of two strongly capacitively coupled quantum dots (QDs), each being independently connected to a side gate which in general exhibits a fluctuating electrostatic field ({\em i.e.}, Johnson-Nyquist noise). Two quantum phases are found: the Kondo phase where an orbital- Kondo entanglement emerges and a local moment phase in which the noise destroys the Kondo effect leaving the orbital spin unscreened and resulting in a clear suppression of the conductance. In the Kondo realm, the cotunneling differs from the usual cotunneling through a single dot due to the peculiar phase space for particle-hole excitations; The transfer of charge across the setting is also accompanied by zero-point charge fluctuations in the two dissipative environments and the I-V characteristics are governed by what we call dissipative cotunneling. [Preview Abstract] |
Thursday, March 24, 2005 11:39AM - 11:51AM |
V17.00003: On-site confinement of excitations in a strongly anisotropic Heisenberg spin and qubit chain Lea Santos, Mark Dykman We study localization of many-excitation states in a system of spins and qubits, and the equivalent problem of many-particle localization of spinless fermions. Recently we proposed a bounded sequence of site energies that leads to the lifetime of all on-site localized single- and many-particle states that is orders of magnitude longer than the reciprocal intersite hopping integral.\footnote{L.F. Santos {\rm et al.}, Phys. Rev. A {\bf 71} (2005).} The method was based on mapping delocalization on particle-particle scattering and eliminating resonant scattering processes up to a high order. However, the required bandwidth of site energies increased linearly with the energy of inter-particle interaction, or with the energy of the Ising part of the spin-spin (qubit-qubit) interaction. It therefore became inconvenient for the models of quantum computers (QCs) where this coupling is strong, such as a QC based on electrons on helium. Here we develop an alternative approach which leads to long localization lifetime for strong interaction for much smaller bandwidth of site energies. It takes advantage of the band-like spectrum of energies that can be transferred in two-particle scattering, with bands being formed by processes where the number of nearest neighbors changes by 0, 1, 2, etc. By opening gaps in the combined site energies in the region of these bands, we can eliminate resonant scattering up to high order in the hopping integral. [Preview Abstract] |
Thursday, March 24, 2005 11:51AM - 12:03PM |
V17.00004: Control of nanodot-cavity-waveguide QED and solid-state quantum network Ren-Bao Liu, Wang Yao, L. J. Sham The interaction of an n-doped nanodot and its electromagnetic environment can be controlled by modifying the quantum states of the environment via cavities and waveguides and driving the dot with optical pulses. Thus an efficient quantum pathway is established to connect in sequence the electron spin states, the trion, the cavity mode, and the photon wavepacket in the waveguide. The photon flying in the directional quantum channel formed by the waveguide, with its shape well-controlled by the optical pulses, can be used either to dump the spin entropy or to carry the quantum information of the spin, which enables the implementations of ultrafast initialization of the spin qubit, quantum non-demolition readout, deterministic single photon sources, and faithful interface between stationary and flying qubits. With these functional elements in hand, scalable quantum networking in solid-state systems is feasible. This work was supported by ARDA/ARO DAAD19-02-1-0183, NSF DMR- 0099572, and QuIST/AFOSR F49620-01-1-0497. [Preview Abstract] |
Thursday, March 24, 2005 12:03PM - 12:15PM |
V17.00005: Coherent rotations of a single spin-based qubit in a single quantum dot at fixed Zeeman energy Jordan Kyriakidis, Stephen Penney Coherent rotations of single spin-based qubits may be accomplished electrically at fixed Zeeman energy with a qubit defined solely within a single electrostatically-defined quantum dot; the $g$-factor and the external magnetic field are kept constant. All that is required to be varied are the voltages on metallic gates which effectively change the shape of the elliptic quantum dot. The pseudospin-1/2 qubit is constructed from the two-dimensional $S=1/2$, $S_z=-1/2$ subspace of three interacting electrons in a two-dimensional potential well. Rotations are created by altering the direction of the pseudomagnetic field through changes in the shape of the confinement potential. By deriving an exact analytic solution to the long-range Coulomb interaction matrix elements, we calculate explicitly the range of magnitudes and directions the pseudomagnetic field can take. Numerical estimates are given for GaAs. [Preview Abstract] |
Thursday, March 24, 2005 12:15PM - 12:27PM |
V17.00006: Singlet current pumping Sungjun Kim, Kunal Das, Ari Mizel We study adiabatic quantum pumping of electron spin singlets in a one dimensional channel. The electron propagation is described using a tight-binding Hamiltonian with two Hubbard impurities. As the strengths of the impurities change periodically in time, a current of spin singlets develops. The calculation employs a two-particle Green's function formalism that assumes no bias in the channel and zero temperature. [Preview Abstract] |
Thursday, March 24, 2005 12:27PM - 12:39PM |
V17.00007: Long-range entanglement and coherent qubit coupling via spin transport: implications for scalability Jacob Taylor, Wolfgang D\"ur, Geza Giedke, Charles Marcus, Peter Zoller, Atac Imamoglu, Mikhail Lukin Solid state approaches to quantum computation offer intriguing prospects for large scale integration and long term stability. Most of the current approaches restrict the computation to nearest-neighbors interactions. This condition generally decreases thresholds for fault tolerant computation. We explore the prospects for improving the scalability of quantum dot-based quantum computation schemes via long range transport of electron spin entangled pairs. Specifically we investigate dominant sources of errors in such a transport and study techniques to purify and correct these errors. Finally, we discuss several approaches for long-lived storage of electronic spin qubits and investigate novel architectures that utilize these resources for scalable quantum computation. [Preview Abstract] |
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