Controlling the interaction of a single quantum emitter with its environment is a key challenge in quantum optics. Here, we demonstrate deterministic coupling of single nitrogen-vacancy ͑NV͒ centers to high-quality photonic crystal cavities. We preselect single NV centers and position their 50-nm-sized host nanocrystals into the mode maximum of photonic crystal S1 cavities with few-nanometer accuracy. The coupling results in a strong enhancement of NV center emission at the cavity wavelength. © 2011 American Institute of Physics. ͓doi:10.1063/1.3571437͔Spontaneous light emission can be controlled by enhancing or suppressing the vacuum fluctuations of the electromagnetic field at the location of the light source. 1 When placed into highly confined optical fields, such as those created in optical cavities or plasmonic structures, the optical properties of single quantum emitters can change drastically. [2][3][4][5] In particular, photonic crystal ͑PC͒ cavities show high quality factors combined with an extremely small mode volume. 6 It is challenging however to efficiently couple single photon sources to a PC cavity because the emitter has to be positioned in the localized optical mode, which is confined to an extremely small volume with a size of about a wavelength. [7][8][9] Nitrogen-vacancy ͑NV͒ centers in diamond are promising candidates for application as solid state quantum bits. [10][11][12] Long distance entanglement between NV centers enabling quantum repeater protocols may be achieved by two-photon quantum interference, 13,14 but is hindered by the NV centers' weak coherent photon emission rate. Being able to control and reshape the emission spectrum of a single NV center is therefore not only of fundamental interest but could also have potential applications in solid state quantum information processing. 15 Fabrication of high-quality PC cavities in diamond would be a natural way to control the emission properties of embedded NV centers but this is challenging because of the difficulties in growing and etching diamond single-crystal thin films. 16,17 An alternative, hybrid approach is to position a diamond nanocrystal with a single NV center near a PC cavity of a different material. [18][19][20][21] Because of the small size of such a crystal, the NV center can be placed in the highly confined optical mode where coupling can be efficient.Here, we demonstrate the deterministic nanoassembly of coupled single NV center-PC cavity systems by positioning ϳ50 nm sized diamond nanocrystals into gallium phosphide S1 cavities located on a different chip. The S1 cavity offers unique advantages over the well-studied L3 cavity. 19,20 Whereas in the L3 cavity the mode maximum is confined within the dielectric material, the mode maximum of the S1 cavity is localized in the air holes surrounding the cavity, making it accessible for coupling to external emitters. We are able to pick up and place a preselected diamond nanocrystal exactly into the mode maximum of a PC cavity, due to the versatility of our nanopositioning ...

Abstract:Hybrid quantum information protocols are based on local qubits, such as trapped atoms, NV centers, and quantum dots, coupled to photons. The coupling is achieved through optical cavities. Here we demonstrate far-field optimized H1 photonic crystal membrane cavities combined with an additional back reflection mirror below the membrane that meet the optical requirements for implementing hybrid quantum information protocols. Using numerical optimization we find that 80% of the light can be radiated within an objective numerical aperture of 0.8, and the coupling to a single-mode fiber can be as high as 92%. We experimentally prove the unique external mode matching properties by resonant reflection spectroscopy with a cavity mode visibility above 50%.

Systems of photonic crystal cavities coupled to quantum dots are a promising architecture for quantum networking and quantum simulators. The ability to independently tune the frequencies of laterally separated quantum dots is a crucial component of such a scheme. Here, we demonstrate independent tuning of laterally separated quantum dots in photonic crystal cavities coupled by in-plane waveguides by implanting lines of protons which serve to electrically isolate different sections of a diode structure.Quantum dots coupled to optical microcavities represent a viable candidate for integrated quantum information technologies such as single photon sources and quantum memory/repeater networks 1-3 . A long-term goal would be to combine on a single chip multiple cavities, each one embedding a single emitter, and connect them through waveguides. Such a system would be a basic building block for a scalable quantum information processing architecture, allowing the implementation of multi-atom entangled states via photon manipulation 4-6 . Furthermore, coupled cavity arrays have been proposed as a quantum simulation tool to investigate the dynamics of quantum many-body systems, originally encountered in condensed-matter physics (like the Bose-Hubbard or Heisenberg models) 7,8 .Photonic crystals are ideal platforms for such a system because defect cavities can easily be integrated with waveguides in the same planar photonic lattice structures 9,10 . Coupling between the cavities and waveguides can be turned off and on relatively easily by, for instance, modifying the local refractive index in a waveguide region via a localized intense laser pulse 11 . A significant barrier to practical implementation of coupled cavity-quantum dots systems is, however, the possibility to independently tune the quantum dot wavelengths in different cavity regions. Because of the large quantum dot ensemble frequency spread of self-assembled InGaAs quantum dots during the growth process, independent frequency control of spatially separated quantum dots is a vital tool. Currently existing methods designed to independently tune different quantum dots have significant limitations. Temperature tuning via local heating 12 requires large distances between the QDs for thermal separation and tends to degrade the quantum dot optical quality at high temperature. Lateral electric field tuning of quantum dots in Schottky diode devices has also been studied 13 , but lateral electric fields provide limited QD emission frequency tuning ranges and do not allow for control of the QD charging states. An ideal tuning mechanism would be all-electrical in implementation and have the flexibility to address quantum dots on any area of the chip with only a small modification of the standard fabrication process.Here, we demonstrate such a mechanism, by implanting protons in a localized area which electrically isolates regions of quantum dots embedded in a diode structure. Ion or proton implantation is used in semiconductor processing as an isolating technique, since it c...

We experimentally characterize the spatial far-field emission profiles for the two lowest confined modes of a photonic crystal cavity of the L3 type, finding a good agreement with FDTD simulations. We then link the far-field profiles to relevant features of the cavity mode near-fields, using a simple Fabry-Perot resonator model. The effect of disorder on far-field cavity profiles is clarified through comparison between experiments and simulations. These results can be useful for emission engineering from active centers embedded in the cavity.

Single quantum emitters can be coupled to photonic crystal (PC) cavities by placing their host nanoparticles into the cavity field. We describe fabrication, characterization, and tuning of gallium-phosphide PC cavities that resonate in the visible, and simulations and measurements of the effect of a nanoparticle on the optical properties of these cavities. Simulations show that introducing a 50 nm (100 nm) sized nanoparticle into S1 and L3-type cavities, with original quality factors of 18 · 10 3 and 73 · 10 3 , respectively, reduces the quality factor by <10% (∼50%). Furthermore, simulations indicate that an emitter embedded in a 50 nm (100 nm) sized nanoparticle can be coupled 3.5 (9) times more effectively to an S1 cavity than to an L3 cavity. We employ a nanopositioning technique to position individual, 50 nm sized nanocrystals into S1 cavities, and find that the quality factors are reduced by a factor of 0.9 0.1 from the original values of order 10 3 .