Nitrogen-vacancy (NV) centers in millimeter-scale diamond samples were produced by irradiation and subsequent annealing under varied conditions. The optical and spin relaxation properties of these samples were characterized using confocal microscopy, visible and infrared absorption, and optically detected magnetic resonance. The sample with the highest NV concentration, approximately 16 ppm (2.8 × 10 18 cm −3 ), was prepared with no observable traces of neutrally-charged vacancy defects. The eective transverse spin-relaxation time for this sample was T * 2 = 118(48) ns, predominately limited by residual paramagnetic nitrogen which was determined to have a concentration of 49(7) ppm. Under ideal conditions, the shot-noise limited sensitivity is projected to be ∼ 150 fT/ √ Hz for a 100 µm-scale magnetometer based on this sample. Other samples with NV concentrations from .007 to 12 ppm and eective relaxation times ranging from 27 to over 291 ns were prepared and characterized.

We demonstrate coupling of the zero-phonon line of individual nitrogen-vacancy centers and the modes of microring resonators fabricated in single-crystal diamond. A zero-phonon line enhancement exceeding ten-fold is estimated from lifetime measurements at cryogenic temperatures. The devices are fabricated using standard semiconductor techniques and off-the-shelf materials, thus enabling integrated diamond photonics.Integrated quantum photonic technologies are key for future applications in quantum information [1, 2], ultralow-power opto-electronics [3], and sensing [4]. As individual quantum bits, nitrogen-vacancy (NV) centers in diamond are among the most attractive solid-state systems identified to date, owing to their long-lived electron and nuclear spin coherence, and capability for individual optical initialization, readout and information storage [5][6][7][8][9]. The major outstanding problem is interconnecting many NVs for large-scale computation. One of the most promising approaches is to couple them to optical resonators, that enhance the zero-phonon line (ZPL) emission, and can be further interconnected in a photonic network [10][11][12].

The zero-phonon transition rate of a nitrogen-vacancy center is enhanced by a factor of ∼ 70 by coupling to a photonic crystal resonator fabricated in monocrystalline diamond using standard semiconductor fabrication techniques. Photon correlation measurements on the spectrally filtered zero-phonon line show antibunching, a signature that the collected photoluminescence is emitted primarily by a single nitrogen-vacancy center. The linewidth of the coupled nitrogen-vacancy center and the spectral diffusion are characterized using high-resolution photoluminescence and photoluminescence excitation spectroscopy.Nitrogen-vacancy (NV) centers in diamond represent one of the best test-beds for future quantum photonic technologies [1, 2] due to their outstanding properties as spin qubits [3] that can be coupled to optical photons [4]. Applications include quantum information [5] and electro-magnetic field sensing [6][7][8]. For quantum information applications, multiple NV centers need to be interconnected. One approach relies on integrating NVs in photonic networks, where large-scale entanglement between NV centers is created using interference of identical photons at the zero-phonon line (ZPL) frequency. However, in bulk diamond the ZPL transition accounts for only a few percent of the NV emission. Here we report ∼ 70 fold enhancement of the transition rate through the ZPL for a single NV coupled to a photonic crystal cavity in monocrystalline diamond. These cavities are fabricated using scalable semiconductor fabrication techniques and can be further coupled into photonic networks [2].The spontaneous emission rate enhancement of a particular dipole transition i of an emitter coupled to a microresonator relative to the uniform dielectric medium of the resonator is enhanced by the factor τ0where 1/τ 0 is the emission rate in the uniform dielectric medium, 1/τ leak is the emission rate outside the cavity mode, and

No abstract

We describe a method to project photonic two-qubit states onto the symmetric and antisymmetric subspaces of their Hilbert space. This device utilizes an ancillary coherent state, together with a weak cross-Kerr non-linearity, generated, for example, by electromagnetically induced transparency. The symmetry analyzer is non-destructive, and works for small values of the cross-Kerr coupling. Furthermore, this device can be used to construct a non-destructive Bell state detector. 03.67.Hk, 42.50.Gy, Two-qubit measurements are an important resource in Quantum Information Processing (QIP), enabling key applications such as the teleportation of states and gate, dense coding and error correction. In particular, a measurement device that does not destroy the qubits is a very powerful tool, since it allows entanglement distillation [1] and efficient quantum computing based on measurements [2,3,4]. This is especially useful when the qubits interact weakly, and interaction-based quantum gates are hard to implement (for example, photonic qubits have negligible interaction). Furthermore, a non-destructive two-qubit measurement device can act as an deterministic source of entangled qubits.Optical QIP is of special interest, because electromagnetic fields are ideal information carriers for long distance quantum communication. Photonic quantum states generally suffer low decoherence rates compared to most massive qubit systems, but we need optical information processing devices that overcome the negligible interaction between the photons. Optical quantum computation and communication will therefore benefit greatly from non-destructive two-qubit measurements. Arguably the most important two-photon measurement is the measurement in the maximally entangled Bell basis. When the computational basis of a single-photon qubit is given by two orthogonal polarization states (H and V ), then the Bell states can be written asA non-destructive Bell measurement then projects the two photons onto one of the Bell states. This can be used in the teleportation of probabilistic gates into optical circuits [5,6], and consequently enables efficient linear optical quantum computing. In addition, a deterministic non-destructive Bell measurement would also act as a bright source of entangled photons.Braunstein and Mann presented a linear optical method to distinguish two out of the four optical Bell states [7]. In 1999, it was shown independently by Vaidman and Yoran, and Lütkenhaus et al. that the Braunstein-Mann method is optimal [8, 9]: When one is restricted to linear optics and photon counting (in-cluding feed-forward processing) at most half of the Bell states can be identified perfectly. This detection method is therefore probabilistic. Furthermore, it destroys the photons in the photon counting process, and is thus of limited use in efficient large-scale QIP.One way to improve on this scheme is to move beyond linear optics, i.e. to induce an interaction between the photons. This can be achieved using a cross-Kerr medium, i.e., a nonlinear mediu...