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 ($V_{eff}$) 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 $V_{eff}<0.2(\lambda/n)^3$. The estimates of $Q$ and $V_{eff}$ 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