30,411 research outputs found
Quantum-dot-spin single-photon interface
Using background-free detection of spin-state-dependent resonance
fluorescence from a single-electron charged quantum dot with an efficiency of
0:1%, we realize a single spin-photon interface where the detection of a
scattered photon with 300 picosecond time resolution projects the quantum dot
spin to a definite spin eigenstate with fidelity exceeding 99%. The bunching of
resonantly scattered photons reveals information about electron spin dynamics.
High-fidelity fast spin-state initialization heralded by a single photon
enables the realization of quantum information processing tasks such as
non-deterministic distant spin entanglement. Given that we could suppress the
measurement back-action to well below the natural spin-flip rate, realization
of a quantum non-demolition measurement of a single spin could be achieved by
increasing the fluorescence collection efficiency by a factor exceeding 20
using a photonic nanostructure
Polarons in semiconductor quantum-dots and their role in the quantum kinetics of carrier relaxation
While time-dependent perturbation theory shows inefficient carrier-phonon
scattering in semiconductor quantum dots, we demonstrate that a quantum kinetic
description of carrier-phonon interaction predicts fast carrier capture and
relaxation. The considered processes do not fulfill energy conservation in
terms of free-carrier energies because polar coupling of localized quantum-dot
states strongly modifies this picture.Comment: 6 pages, 6 figures, accepted for publication in Phys.Rev.
Loss Tolerant Optical Qubits
We present a linear optics quantum computation scheme that employs a new
encoding approach that incrementally adds qubits and is tolerant to photon loss
errors. The scheme employs a circuit model but uses techniques from cluster
state computation and achieves comparable resource usage. To illustrate our
techniques we describe a quantum memory which is fault tolerant to photon loss
Loss-tolerant operations in parity-code linear optics quantum computing
A heavy focus for optical quantum computing is the introduction of
error-correction, and the minimisation of resource requirements. We detail a
complete encoding and manipulation scheme designed for linear optics quantum
computing, incorporating scalable operations and loss-tolerant architecture.Comment: 8 pages, 6 figure
Quantum information processing with single photons and atomic ensembles in microwave coplanar waveguide resonators
We show that pairs of atoms optically excited to the Rydberg states can
strongly interact with each other via effective long-range dipole-dipole or van
der Waals interactions mediated by their non-resonant coupling to a common
microwave field mode of a superconducting coplanar waveguide cavity. These
cavity mediated interactions can be employed to generate single photons and to
realize in a scalable configuration a universal phase gate between pairs of
single photon pulses propagating or stored in atomic ensembles in the regime of
electromagnetically induced transparency
Mesoporous matrices for quantum computation with improved response through redundance
We present a solid state implementation of quantum computation, which improves previously proposed optically driven schemes. Our proposal is based on vertical arrays of quantum dots embedded in a mesoporous material which can be fabricated with present technology. The redundant encoding typical of the chosen hardware protects the computation against gate errors and the effects of measurement induced noise. The system parameters required for quantum computation applications are calculated for II-VI and III-V materials and found to be within the experimental range. The proposed hardware may help minimize errors due to polydispersity of dot sizes, which is at present one of the main problems in relation to quantum dot-based quantum computation. (c) 2007 American Institute of Physics
Entanglement Witnesses from Single-Particle Interference
We describe a general method of realizing entanglement witnesses in terms of
the interference pattern of a single quantum probe. After outlining the
principle, we discuss specific realizations both with electrons in mesoscopic
Aharonov-Bohm rings and with photons in standard Young's double-slit or
coherent-backscattering interferometers.Comment: 5 pages, 3 figures, epl2, uses pstricks.st
Stability of quantum motion and correlation decay
We derive a simple and general relation between the fidelity of quantum
motion, characterizing the stability of quantum dynamics with respect to
arbitrary static perturbation of the unitary evolution propagator, and the
integrated time auto-correlation function of the generator of perturbation.
Surprisingly, this relation predicts the slower decay of fidelity the faster
decay of correlations is. In particular, for non-ergodic and non-mixing
dynamics, where asymptotic decay of correlations is absent, a qualitatively
different and faster decay of fidelity is predicted on a time scale 1/delta as
opposed to mixing dynamics where the fidelity is found to decay exponentially
on a time-scale 1/delta^2, where delta is a strength of perturbation. A
detailed discussion of a semi-classical regime of small effective values of
Planck constant is given where classical correlation functions can be used to
predict quantum fidelity decay. Note that the correct and intuitively expected
classical stability behavior is recovered in the classical limit hbar->0, as
the two limits delta->0 and hbar->0 do not commute. In addition we also discuss
non-trivial dependence on the number of degrees of freedom. All the theoretical
results are clearly demonstrated numerically on a celebrated example of a
quantized kicked top.Comment: 32 pages, 10 EPS figures and 2 color PS figures. Higher resolution
color figures can be obtained from authors; minor changes, to appear in
J.Phys.A (March 2002
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