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The negatively-charged nitrogen-vacancy centers in diamond has motivated many groups building scalable quantum information processors based on diamond photonics. This is owning to the long-lived electronic spin coherence and the capability for spin manipulation and readout of NV centers.1-4 The primitive operation is to create entanglement between two NV centers, based on schemes such as 'atom-photon entanglement' proposed by Cabrillo et al.5To scale this type of scheme beyond two qubits, one important component is an optical switch that allows light emitted from a particular device to be routed to multiple locations. With such a switch, one has choices of routing photons to specified paths and has the benefit of improving the entanglement speed by entangling multiple qubits at the same time. Yield of the existing diamond cavities coupled with NV centers are inevitably low, due to the nature of randomness for NV placement and orientation, variation of spectral stability, and variation of cavity resonance frequency and quality factor. An optical switch provides the capability to tolerate a large fraction of defective devices by routing only to the working devices. Many type of switching devices were built on conventional semiconductor materials with mechanisms from mechanical, thermal switching to carrier injection, photonics crystal, and polymer refractive index tuning .6-8 In this paper, we build an optical-thermal switch on diamond with micro-ring waveguides, mainly for the simplicity of the diamond fabrication. The the switching function was realized by locally tuning the temperature of the diamond waveguides. Switching efficiency of 31% at 'drop' port and 73% at 'through' port were obtained.

We demonstrate coupling between the zero phonon line (ZPL) of nitrogen-vacancy centers in diamond and the modes of optical micro-resonators fabricated in single crystal diamond membranes sitting on a silicon dioxide substrate. A more than ten-fold enhancement of the ZPL is estimated by measuring the modification of the spontaneous emission lifetime. The cavity-coupled ZPL emission was further coupled into on-chip waveguides thus demonstrating the potential to build optical quantum networks in this diamond on insulator platform.

The combination of the long electron state spin coherence time and the optical coupling of the ground electronic states to an excited state manifold makes the nitrogen-vacancy (NV) center in diamond an attractive candidate for quantum information processing. To date the best spin and optical properties have been found in centers deep within the diamond crystal. For useful devices it will be necessary to engineer NVs with similar properties close to the diamond surface. We report on properties including charge state control and preferential orientation for near surface NVs formed either in CVD growth or through implantation and annealing. © 2011 SPIE., Advances in Photonics of Quantum Computing, Memory, and Communication IV, January 25-27, 2011, San Francisco, CA, USA, Series: Proceedings of SPIE

Nitrogen-vacancy centers in diamond are widely studied both as a testbed for solid state quantum optics and for their applications in quantum information processing and magnetometry. Here we demonstrate coupling of the nitrogen-vacancy centers to gap plasmons in metal nano-slits. We use diamond samples where nitrogen-vacancy centers are implanted tens of nanometers under the surface. Silver nano-slits are patterned on the sample such that diamond ridges tens of nanometers wide fill the slit gap. We measure enhancement of the spontaneous emission rate of the zero photon line by a factor of 3 at a temperature of 8K.

Ultrasound-modulated optical tomography is a hybrid imaging technique based on detection of the diffused light modulated by a focused ultrasonic wave inside a scattering medium. With the combined advantages of ultrasonic resolution and optical contrast, UOT is ideal for deep tissue imaging. Its growth in popularity and application, however, is hindered by the low efficiency in detecting the modulated diffused photons. Research activities on UOT have therefore been centered on improving its signal detection efficiency by exploring various technical solutions. A prime example is the use of spectral-hole burning (SHB) in UOT. By applying SHB crystal as a spectral filter, one modulation sideband of the diffused light can be efficiently selected while all the other frequency components are strongly suppressed. Immune to both the spatial and temporal incoherence of the signal with a high enough on/off ratio, SHB can boost the UOT imaging ability dramatically and push it towards practical applications. We compare SHB with the other technologies that have been applied to UOT, and identify the unique features that make SHB a preferable tool for UOT. We also discuss the desired improvements from the SHB side, which will help UOT pave the way from research to everyday life.

Single InAs quantum dots can be used to control the transmission function of photonic crystal cavities, as we have already shown for systems that operate both in strong and weak coupling regime. Here we present our most recent work on devices where the cavity is connected in a micron-scale optical network via multiple photonic crystal waveguides terminated with input and output optical couplers. This architecture allows for multiple signal and control beams to be coupled simultaneously in the cavity via distinct ports. The devices are equipped with two input ports where the waveguides are terminated with input grating-couplers that allow for coupling into the waveguide from an out-of-plane direction. A third waveguide coupled to the cavity is terminated with a different kind of grating out-coupler that allows for improved directional scattering of the light transmitted through the cavity. We have already shown in previous experiments with a single cavity with coupled quantum dots, that this system acts as a highly nonlinear medium that enables all optical switching at powers down to the single photon level. In our most recent experiments we take significant steps towards demonstrating that this switching can be done in integrated structures, as needed for optical signal processing devices for both classical and quantum information science.

The single photon character of nonclassical states of light that can be generated using photon blockade is analyzed for time domain operation. We show that improved single photon statistics (single photon around 85% with a multi-photon of 8%) can be obtained by adequately choosing the parameters (mainly amplitude and pulse-duration) of the driving laser pulses. An alternative method, where the system is driven via a continuous wave laser and the frequency of the dipole is controlled (e.g. electrically) at very fast timescales is presented. We also show that this non-classical state performs better than a weak coherent pulse, when applied to BB84 quantum cryptography protocol.

In this paper, we review some recent cavity quantum electrodynamic (CQED) experiments with single quantum dot exciton coupled to photonic crystal cavities, performed in our group. We show how the coupled quantum-dot/cavity system can be used to modulate light with at a very fundamental level with very low power and discuss some applications of these low power modulators.