Hybrid Nanocavity Resonant Enhancement of Color Center Emission in Diamond

Abstract

Resonantly enhanced emission from the zero-phonon line of a diamond nitrogen-vacancy (NV) center in single crystal diamond is demonstrated experimentally using a hybrid whispering gallery mode nanocavity. A 900 nm diameter ring nanocavity formed from gallium phosphide, whose sidewalls extend into a diamond substrate, is tuned onto resonance at a low temperature with the zero-phonon line of a negatively charged NV center implanted near the diamond surface. When the nanocavity is on resonance, the zero-phonon line intensity is enhanced by approximately an order of magnitude, and the spontaneous emission lifetime of the NV is reduced by as much as 18%, corresponding to a 6.3X enhancement of emission in the zero photon line. DOI: 10.1103/PhysRevX.1.011007 Subject Areas: Nanophysics, Photonics, Quantum InformationThe diamond nitrogen-vacancy (NV) center is an optically active impurity which combines many of the desirable properties of quantum dots and laser-trapped atoms. Optical transitions of diamond NV centers can display low inhomogeneous broadening, and have been used to generate single photons [1], manipulate single electron spins [2], and control nearby nuclear spin impurities [3][4][5]. Remarkably, the room temperature electron spin coherence times of NVs can exceed a millisecond [6]. These properties make NVs a promising qubit for proposed quantum networks [7], and an attractive system for applications such as magnetometry [8] and low power optical switching [9]. An outstanding challenge limiting the use of NV centers as qubits in quantum information processing is the creation of a platform for mediating interactions between them. A promising approach to this problem is to create an onchip quantum network in which NVs interact optically via nanophotonic interconnects [10]. Coupling NVs to optical cavities plays a crucial role in this implementation by enhancing the NV emission into a well-defined optical mode, which can be efficiently coupled to waveguides and routed on-chip. Cavity enhancement of the emission is particularly important for NV centers, as it provides a means for increasing the relative brightness of the narrowband zero-phonon line (ZPL) emission relative to the broadband phonon assisted emission. The selection of the emission into the ZPL is necessary for protocols involving coherent interactions or indistinguishable photons.Demonstrating diamond-based quantum networks has recently prompted significant research into integrating NV centers with photonic devices [11]. Efforts to efficiently couple NVs in nanocrystalline diamond to nanophotonic structures [12][13][14][15] have been limited by poor NV optical properties in nanocrystals compared to those found in single crystal diamond. Fabricating nanophotonic devices directly from single crystal diamond has recently made important progress [11,16,17], limited primarily by fabrication difficulties related to creating thin films of single crystal diamond necessary for optical confinement in three dimensions. An alternative approach, which levera...

Waveguide-integrated single-crystalline GaP resonators on diamond

“…The ZPL emission makes up only a small fraction of the total spontaneous emission rate γ NV : ~ 3% [11,22,23]. However, if an NV -is placed within the field of a hybrid GaP/diamond cavity, its emission rate into the ZPL can be enhanced by a Purcell factor F ZPL [19,24]. Under weak coupling, the enhancement is given by…”

“…Coupling of the optical emission of near-surface NV -defects in diamond to isolated GaP optical resonators and Purcell enhancement in these structures has previously been demonstrated [18,19]. However, the fabrication approach utilized does not allow for the deterministic placement of those resonators on the substrate, and hence cannot be employed for the fabrication of waveguide-integrated cavity structures.…”

Design and low-temperature characterization of a tunable microcavity for diamond-based quantum networks

“…6 Purcell enhancement of the ZPL has been demonstrated in several cavity architectures such as diamond photonic crystal cavities, 7-11 microring resonators, 12 and hybrid structures with evanescently coupled nanodiamonds. [13][14][15][16] In recent years, the open Fabry-Perot microcavity 17 has emerged as a promising platform for diamond emitters. [18][19][20][21][22] Such a microcavity provides in-situ spatial and spectral tunability, while reaching strong field confinement due to its small mode volume V and high quality factor Q.…”

Hybrid Group IV Nanophotonic Structures Incorporating Diamond Silicon-Vacancy Color Centers

“…9,10 Hybrid solid- state schemes consisting of quantum emitters in individual nanocrystals coupled to semiconductor optical cavities in other materials have also been demonstrated; 11 however, they typically require AFM 'pick-and-place' assembly techniques 12 or complex film transfers. [13][14][15][16] Silicon-vacancy (SiV − ) color centers in diamond have recently emerged as promising candidates for QIP applications. 17 Due to the inversion symmetry of the SiV − centers, they display superior spectral stability and narrow inhomogeneous broadening, with room temperature linewidths of a few nanometers and nearly transform-limited linewidths at low temperature.…”