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].

A technique is demonstrated which efficiently transfers light between a tapered standard single-mode optical fiber and a high-Q, ultra-small mode volume, silicon photonic crystal resonant cavity. Cavity mode quality factors of 4.7x10(4) are measured, and a total fiber-to-cavity coupling efficiency of 44% is demonstrated. Using this efficient cavity input and output channel, the steady-state nonlinear absorption and dispersion of the photonic crystal cavity is studied. Optical bistability is observed for fiber input powers as low as 250 microW, corresponding to a dropped power of 100 microW and 3 fJ of stored cavity energy. A high-density effective free-carrier lifetime for these silicon photonic crystal resonators of ~ 0.5 ns is also estimated from power dependent loss and dispersion measurements.

The optical transition linewidth and emission polarization of single nitrogen-vacancy (NV) centers are measured from 5 K to room temperature. Interexcited state population relaxation is shown to broaden the zero-phonon line and both the relaxation and linewidth are found to follow a T(5) dependence for T < 100 K. This dependence indicates that the dynamic Jahn-Teller effect is the dominant dephasing mechanism for the NV optical transitions at low temperatures.

The conversion of neutral nitrogen-vacancy centers to negatively charged nitrogen-vacancy centers is demonstrated for centers created by ion implantation and annealing in high-purity diamond. Conversion occurs with surface exposure to an oxygen atmosphere at 465 °C. The spectral properties of the charge-converted centers are investigated. Charge state control of nitrogen-vacancy centers close to the diamond surface is an important step toward the integration of these centers into devices for quantum information and magnetic sensing applications.

Dissipative and dispersive optomechanical couplings are experimentally observed in a photonic crystal split-beam nanocavity optimized for detecting nanoscale sources of torque. Dissipative coupling of up to approximately $500$ MHz/nm and dispersive coupling of $2$ GHz/nm enable measurements of sub-pg torsional and cantilever-like mechanical resonances with a thermally-limited torque detection sensitivity of 1.2$\times 10^{-20} \text{N} \, \text{m}/\sqrt{\text{Hz}}$ in ambient conditions and 1.3$\times 10^{-21} \text{N} \, \text{m}/\sqrt{\text{Hz}}$ in low vacuum. Interference between optomechanical coupling mechanisms is observed to enhance detection sensitivity and generate a mechanical-mode-dependent optomechanical wavelength response.Comment: 11 pages, 6 figure

High refractive index contrast optical microdisk resonators fabricated from silicon-on-insulator wafers are studied using an external silica fiber taper waveguide as a wafer-scale optical probe. Measurements performed in the 1500 nm wavelength band show that these silicon microdisks can support whispering-gallery modes with quality factors as high as 5.2ϫ 10 5 , limited by Rayleigh scattering from fabrication induced surface roughness. Microdisks with radii as small as 2.5 m are studied, with measured quality factors as high as 4. 7ϫ 10 6 Applications for such devices include quantum networking, 7 low threshold nonlinear optical sources, 8 and compact micro-optical circuits. 4 The ability to create similar high quality factor ͑Q͒ WGM resonators in III-V or silicon ͑Si͒ semiconductors has thus far been hampered by the large refractive index of most semiconductors and the resulting sensitivity to surface roughness. 9,10 In this letter we describe measurements of micron-sized Si microdisk resonators supporting TM WGMs with significantly reduced sensitivity to disk-edge roughness. These modes have measured Q values as high as 5.2ϫ 10 5 and effective modal volumes ͑V eff ͒ as small as 5.3 cubic wavelengths in the material. The largest Q / V eff ratio is measured to be 8.8ϫ 10 4 , greater than the values measured in ultrasmall volume photonic crystals 11 and comparable to the values measured in ultrahigh-Q microspheres and microtoroids.

Optical microcavities and waveguides coupled to diamond are needed to enable efficient communication between quantum systems such as nitrogen-vacancy centers which are known already to have long electron spin coherence lifetimes. This paper describes recent progress in realizing microcavities with low loss and small mode volume in two hybrid systems: silica microdisks coupled to diamond nanoparticles, and gallium phosphide microdisks coupled to single-crystal diamond. A theoretical proposal for a gallium phosphide nanowire photonic crystal cavity coupled to diamond is also discussed. Comparing the two material systems, silica microdisks are easier to fabricate and test. However, at low temperature, nitrogen-vacancy centers in bulk diamond are spectrally more stable, and we expect that in the long term the bulk diamond approach will be better suited for on-chip integration of a photonic network.