12,884 research outputs found
Photon-Mediated Quantum Gate between Two Trapped Neutral Atoms in an Optical Cavity
Quantum logic gates are fundamental building blocks of quantum computers.
Their integration into quantum networks requires strong qubit coupling to
network channels, as can be realized with neutral atoms and optical photons in
cavity quantum electrodynamics. Here we demonstrate that the long-range
interaction mediated by a flying photon performs a gate between two stationary
atoms inside an optical cavity from which the photon is reflected. This single
step executes the gate in . We show an entangling operation
between the two atoms by generating a Bell state with 76(2)% fidelity. The gate
also operates as a CNOT. We demonstrate 74.1(1.6)% overlap between the observed
and the ideal gate output, limited by the state preparation fidelity of
80.2(0.8)%. As the atoms are efficiently connected to a photonic channel, our
gate paves the way towards quantum networking with multiqubit nodes and the
distribution of entanglement in repeater-based long-distance quantum networks.Comment: 10 pages including appendix, 5 figure
Linear optics quantum Toffoli and Fredkin gates
We design linear optics multiqubit quantum logic gates. We assume the
traditional encoding of a qubit onto state of a single photon in two modes
(e.g. spatial or polarization). We suggest schemes allowing direct
probabilistic realization of the fundamental Toffoli and Fredkin gates without
resorting to a sequence of single- and two-qubit gates. This yields more
compact schemes and potentially reduces the number of ancilla photons. The
proposed setups involve passive linear optics, sources of auxiliary single
photons or maximally entangled pairs of photons, and single-photon detectors.
In particular, we propose an interferometric implementation of the Toffoli gate
in the coincidence basis, which does not require any ancilla photons and is
experimentally feasible with current technology.Comment: 8 pages, 4 figures, RevTeX
Heralded Storage of a Photonic Quantum Bit in a Single Atom
Combining techniques of cavity quantum electrodynamics, quantum measurement,
and quantum feedback, we have realized the heralded transfer of a polarization
qubit from a photon onto a single atom with 39% efficiency and 86% fidelity.
The reverse process, namely, qubit transfer from the atom onto a given photon,
is demonstrated with 88% fidelity and an estimated efficiency of up to 69%. In
contrast to previous work based on two-photon interference, our scheme is
robust against photon arrival-time jitter and achieves much higher
efficiencies. Thus, it constitutes a key step toward the implementation of a
long-distance quantum network.Comment: 6 pages, 4 figure
Repeat-Until-Success quantum computing using stationary and flying qubits
We introduce an architecture for robust and scalable quantum computation
using both stationary qubits (e.g. single photon sources made out of trapped
atoms, molecules, ions, quantum dots, or defect centers in solids) and flying
qubits (e.g. photons). Our scheme solves some of the most pressing problems in
existing non-hybrid proposals, which include the difficulty of scaling
conventional stationary qubit approaches, and the lack of practical means for
storing single photons in linear optics setups. We combine elements of two
previous proposals for distributed quantum computing, namely the efficient
photon-loss tolerant build up of cluster states by Barrett and Kok [Phys. Rev.
A 71, 060310(R) (2005)] with the idea of Repeat-Until-Success (RUS) quantum
computing by Lim et al. [Phys. Rev. Lett. 95, 030505 (2005)]. This idea can be
used to perform eventually deterministic two-qubit logic gates on spatially
separated stationary qubits via photon pair measurements. Under non-ideal
conditions, where photon loss is a possibility, the resulting gates can still
be used to build graph states for one-way quantum computing. In this paper, we
describe the RUS method, present possible experimental realizations, and
analyse the generation of graph states.Comment: 14 pages, 7 figures, minor changes, references and a discussion on
the effect of photon dark counts adde
Corpuscular Event-by-Event Simulation of Quantum Optics Experiments: Application to a Quantum-Controlled Delayed-Choice Experiment
A corpuscular simulation model of optical phenomena that does not require the
knowledge of the solution of a wave equation of the whole system and reproduces
the results of Maxwell's theory by generating detection events one-by-one is
discussed. The event-based corpuscular model gives a unified description of
multiple-beam fringes of a plane parallel plate and single-photon Mach-Zehnder
interferometer, Wheeler's delayed choice, photon tunneling, quantum eraser,
two-beam interference, Einstein-Podolsky-Rosen-Bohm and Hanbury Brown-Twiss
experiments. The approach is illustrated by application to a recent proposal
for a quantum-controlled delayed choice experiment, demonstrating that also
this thought experiment can be understood in terms of particle processes only.Comment: Invited paper presented at FQMT11. Accepted for publication in
Physica Scripta 27 June 201
Photonic architecture for scalable quantum information processing in NV-diamond
Physics and information are intimately connected, and the ultimate
information processing devices will be those that harness the principles of
quantum mechanics. Many physical systems have been identified as candidates for
quantum information processing, but none of them are immune from errors. The
challenge remains to find a path from the experiments of today to a reliable
and scalable quantum computer. Here, we develop an architecture based on a
simple module comprising an optical cavity containing a single
negatively-charged nitrogen vacancy centre in diamond. Modules are connected by
photons propagating in a fiber-optical network and collectively used to
generate a topological cluster state, a robust substrate for quantum
information processing. In principle, all processes in the architecture can be
deterministic, but current limitations lead to processes that are probabilistic
but heralded. We find that the architecture enables large-scale quantum
information processing with existing technology.Comment: 24 pages, 14 Figures. Comment welcom
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