242 research outputs found
Investigation of defect cavities formed in three-dimensional woodpile photonic crystals
We report the optimisation of optical properties of single defects in
three-dimensional (3D) face-centred-cubic (FCC) woodpile photonic crystal (PC)
cavities by using plane-wave expansion (PWE) and finite-difference time-domain
(FDTD) methods. By optimising the dimensions of a 3D woodpile PC, wide photonic
band gaps (PBG) are created. Optical cavities with resonances in the bandgap
arise when point defects are introduced in the crystal. Three types of single
defects are investigated in high refractive index contrast (Gallium
Phosphide-Air) woodpile structures and Q-factors and mode volumes ()
of the resonant cavity modes are calculated. We show that, by introducing an
air buffer around a single defect, smaller mode volumes can be obtained. We
demonstrate high Q-factors up to 700000 and cavity volumes down to
. The estimates of and are then used to
quantify the enhancement of spontaneous emission and the possibility of
achieving strong coupling with nitrogen-vacancy (NV) colour centres in diamond.Comment: 12 pages, 11 figure
Experimental demonstration of a graph state quantum error-correction code
Scalable quantum computing and communication requires the protection of
quantum information from the detrimental effects of decoherence and noise.
Previous work tackling this problem has relied on the original circuit model
for quantum computing. However, recently a family of entangled resources known
as graph states has emerged as a versatile alternative for protecting quantum
information. Depending on the graph's structure, errors can be detected and
corrected in an efficient way using measurement-based techniques. In this
article we report an experimental demonstration of error correction using a
graph state code. We have used an all-optical setup to encode quantum
information into photons representing a four-qubit graph state. We are able to
reliably detect errors and correct against qubit loss. The graph we have
realized is setup independent, thus it could be employed in other physical
settings. Our results show that graph state codes are a promising approach for
achieving scalable quantum information processing
Giant optical Faraday rotation induced by a single electron spin in a quantum dot: Applications to entangling remote spins via a single photon
We propose a quantum non-demolition method - giant Faraday rotation - to
detect a single electron spin in a quantum dot inside a microcavity where
negatively-charged exciton strongly couples to the cavity mode. Left- and
right-circularly polarized light reflected from the cavity feels different
phase shifts due to cavity quantum electrodynamics and the optical spin
selection rule. This yields giant and tunable Faraday rotation which can be
easily detected experimentally. Based on this spin-detection technique, a
scalable scheme to create an arbitrary amount of entanglement between two or
more remote spins via a single photon is proposed.Comment: 5 pages, 3 figure
Investigation of a single-photon source based on quantum interference
We report on an experimental investigation of a single-photon source based on
a quantum interference effect first demonstrated by Koashi, Matsuoka, and
Hirano [Phys. Rev. A 53, 3621 (1996)]. For certain types of measurement-based
quantum information processing applications this technique may be useful as a
high rate, but random, source of single photons.Comment: Submitted to the New J. Phys. Focus Issue on "Measurement-based
quantum information processing
Probabilistic Quantum Encoder for Single-Photon Qubits
We describe an experiment in which a physical qubit represented by the
polarization state of a single-photon was probabilistically encoded in the
logical state of two photons. The experiment relied on linear optics,
post-selection, and three-photon interference effects produced by a parametric
down-conversion photon pair and a weak coherent state. An interesting
consequence of the encoding operation was the ability to observe entangled
three-photon Greenberger-Horne-Zeilinger states.Comment: 4 pages, 4 figures; submitted to Phys. Rev.
Quantum-scissors device for optical state truncation: A proposal for practical realization
We propose a realizable experimental scheme to prepare superposition of the
vacuum and one-photon states by truncating an input coherent state. The scheme
is based on the quantum scissors device proposed by Pegg, Phillips, and Barnett
[Phys. Rev. Lett. 81, 1604 (1998)] and uses photon-counting detectors, a
single-photon source, and linear optical elements. Realistic features of the
photon counting and single-photon generation are taken into account and
possible error sources are discussed together with their effect on the fidelity
and efficiency of the truncation process. Wigner function and phase
distribution of the generated states are given and discussed for the evaluation
of the proposed scheme.Comment: 11 pages, 12 figures, the final version to appear in Phys. Rev. A64,
0638xx (2001
Poles and zeros of the scattering matrix associated to defect modes
We analyze electromagnetic waves propagation in one-dimensional periodic
media with single or periodic defects. The study is made both from the point of
view of the modes and of the diffraction problem. We provide an explicit
dispersion equation for the numerical calculation of the modes, and we
establish a connection between modes and poles and zeros of the scattering
matrix.Comment: 6 pages (Revtex), no figure
Modelling Defect Cavities Formed in Inverse Three-Dimensional Rod-Connected Diamond Photonic Crystals
Defect cavities in 3D photonic crystal can trap and store light in the
smallest volumes allowable in dielectric materials, enhancing non-linearities
and cavity QED effects. Here, we study inverse rod-connected diamond (RCD)
crystals containing point defect cavities using plane-wave expansion and
finite-difference time domain methods. By optimizing the dimensions of the
crystal, wide photonic band gaps are obtained. Mid-bandgap resonances can then
be engineered by introducing point defects in the crystal. We investigate a
variety of single spherical defects at different locations in the unit cell
focusing on high-refractive-index contrast (3.3:1) inverse RCD structures;
quality factors (Q-factors) and mode volumes of the resonant cavity modes are
calculated. By choosing a symmetric arrangement, consisting of a single sphere
defect located at the center of a tetrahedral arrangement, mode volumes < 0.06
cubic wavelengths are obtained, a record for high index cavities.Comment: 7 pages, 8 figure
Strongly enhanced photon collection from diamond defect centres under micro-fabricated integrated solid immersion lenses
The efficiency of collecting photons from optically active defect centres in
bulk diamond is greatly reduced by refraction and reflection at the diamond-air
interface. We report on the fabrication and measurement of a geometrical
solution to the problem; integrated solid immersion lenses (SILs) etched
directly into the surface of diamond. An increase of a factor of 10 was
observed in the saturated count-rate from a single negatively charged
nitrogen-vacancy (NV-) within a 5um diameter SIL compared with NV-s under a
planar surface in the same crystal. A factor of 3 reduction in background
emission was also observed due to the reduced excitation volume with a SIL
present. Such a system is potentially scalable and easily adaptable to other
defect centres in bulk diamond.Comment: 5 Pages, 5 figures (4 subfigures) - corrected typ
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