75 research outputs found
Deterministic atom-light quantum interface
The notion of an atom-light quantum interface has been developed in the past
decade, to a large extent due to demands within the new field of quantum
information processing and communication. A promising type of such interface
using large atomic ensembles has emerged in the past several years. In this
article we review this area of research with a special emphasis on
deterministic high fidelity quantum information protocols. Two recent
experiments, entanglement of distant atomic objects and quantum memory for
light are described in detail.Comment: 50 pages (bookstyle) 15 graphs, to be published in "Advances in
Atomic, Molecular, and Optical Physics" Vol. 54. (2006)(Some of the graphs
here have lower resolution than in the version to be published
Measurement-induced two-qubit entanglement in a bad cavity: Fundamental and practical considerations
An entanglement-generating protocol is described for two qubits coupled to a
cavity field in the bad-cavity limit. By measuring the amplitude of a field
transmitted through the cavity, an entangled spin-singlet state can be
established probabilistically. Both fundamental limitations and practical
measurement schemes are discussed, and the influence of dissipative processes
and inhomogeneities in the qubits are analyzed. The measurement-based protocol
provides criteria for selecting states with an infidelity scaling linearly with
the qubit-decoherence rate.Comment: 13 pages, 7 figures, submitted to Phys. Rev.
Quantum memory for microwave photons in an inhomogeneously broadened spin ensemble
We propose a multi-mode quantum memory protocol able to store the quantum
state of the field in a microwave resonator into an ensemble of electronic
spins. The stored information is protected against inhomogeneous broadening of
the spin ensemble by spin-echo techniques resulting in memory times orders of
magnitude longer than previously achieved. By calculating the evolution of the
first and second moments of the spin-cavity system variables for realistic
experimental parameters, we show that a memory based on NV center spins in
diamond can store a qubit encoded on the |0> and |1> Fock states of the field
with 80% fidelity.Comment: 5 pages, 4 figures, 11 pages supplementary materia
Exciton spin-flip rate in quantum dots determined by a modified local density of optical states
The spin-flip rate that couples dark and bright excitons in self-assembled
quantum dots is obtained from time-resolved spontaneous emission measurements
in a modified local density of optical states. Employing this technique, we can
separate effects due to non-radiative recombination and unambiguously record
the spin-flip rate. The dependence of the spin-flip rate on emission energy is
compared in detail to a recent model from the literature, where the spin flip
is due to the combined action of short-range exchange interaction and acoustic
phonons. We furthermore observe a surprising enhancement of the spin-flip rate
close to a semiconductor-air interface, which illustrates the important role of
interfaces for quantum dot based nanophotonic structures. Our work is an
important step towards a full understanding of the complex dynamics of quantum
dots in nanophotonic structures, such as photonic crystals, and dark excitons
are potentially useful for long-lived coherent storage applications.Comment: 5 pages, 4 figure
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