Kai Mei C Fu

Resonant enhancement of the zero-phonon emission from a colour centre in a diamond cavity

Integrated quantum photonic technologies are key for future applications in quantum information, ultralow-power opto-electronics and sensing. As individual quantum bits, nitrogen-vacancy centres in diamond are among the most promising solid-state systems identified to date, because of their long-lived electron and nuclear spin coherence, and capability for individual optical initialization, readout and information storage. The major outstanding hurdle lies in interconnecting many nitrogen vacancies for large-scale computation. One of the most promising approaches in this regard is to couple them to optical resonators, which can be further interconnected in a photonic network. Here, we demonstrate coupling of the zero-phonon line of individual nitrogen vacancies to the modes of microring resonators fabricated in single-crystal diamond. Zero-phonon line enhancement by more than a factor of 10 is estimated from lifetime measurements. The devices are fabricated using standard semiconductor techniques and off-the-shelf materials, thus enabling integrated diamond photonics.

Diamonds with a high density of nitrogen-vacancy centers for magnetometry applications

V. M. Acosta, E. Bauch, 2 M. P. Ledbetter, C. Santori, K.-M. C. Fu, P. E. Barclay, R. G. Beausoleil, H. Linget, J. F. Roch, F. Treussart, S. Chemerisov, W. Gawlik, and D. Budker 8, 9 1 Department of Physics, University of California, Berkeley, CA 94720-7300 2 Technische Universität Berlin, Hardenbergstraÿe 28, 10623 Berlin, Germany 3 Hewlett-Packard Laboratories, 1501 Page Mill Rd., Palo Alto, CA 94304 4 Ecole Normale Supérieure de Cachan, 61 Avenue du Président Wilson, 94235 Cachan CEDEX, France 5 Laboratoire de Photonique Quantique et Moléculaire (CNRS UMR 8537), Ecole Normale Supérieure de Cachan, 61 Avenue du Président Wilson, 94235 Cachan CEDEX, France 6 Argonne National Laboratory, Argonne, IL, 60439, U.S.A. 7 Center for Magneto-Optical Research, Institute of Physics, Jagiellonian University, Reymonta 4, 30-059 Kraków, Poland Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley CA 94720, USA budker@berkeley.edu (Dated: July 31, 2009)

Chip-based microcavities coupled to nitrogen-vacancy centers in single crystal diamond

Optical coupling of nitrogen-vacancy centers in single-crystal diamond to an on-chip microcavity is demonstrated. The microcavity is fabricated from a hybrid gallium phosphide and diamond material system and supports whispering gallery mode resonances with spectrometer resolution limited Q>25 000.

Conversion of neutral nitrogen-vacancy centers to negatively charged nitrogen-vacancy centers through selective oxidation

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.

Coherent interference effects in a nano-assembled diamond NV center cavity-QED system.

Diamond nanocrystals containing NV color centers are positioned with 100-nanometer-scale accuracy in the near-field of a high-Q SiO(2) microdisk cavity using a fiber taper. The cavity modified nanocrystal photoluminescence is studied, with Fano-like quantum interference features observed in the far-field emission spectrum. A quantum optical model of the system is proposed and fit to the measured spectra, from which the NV(-) zero phonon line coherent coupling rate to the microdisk is estimated to be 28 MHz for a nearly optimally placed nanocrystal.

Nanophotonics for quantum optics using nitrogen-vacancy centers in diamond

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.

Vertical distribution of nitrogen-vacancy centers in diamond formed by ion implantation and annealing

Etching experiments were performed that reveal the vertical distribution of optically active nitrogen-vacancy (NV) centers in diamond created in close proximity to a surface through ion implantation and annealing. The NV distribution depends strongly on the native nitrogen concentration, and spectral measurements of the neutral and negatively-charged NV peaks give evidence for electron depletion effects in lower-nitrogen material. The results are important for potential quantum information and magnetometer devices where NV centers must be created in close proximity to a surface for coupling to optical structures.

Coupling of nitrogen-vacancy centers in diamond to a GaP waveguide

The optical coupling of guided modes in a GaP waveguide to nitrogen-vacancy (NV) centers in diamond is demonstrated. The electric field penetration into diamond and the loss of the guided mode are measured. The results indicate that the GaP-diamond system could be useful in realizing coupled microcavity-NV devices for quantum information processing in diamond.

Hybrid photonic crystal cavity and waveguide for coupling to diamond NV-centers

A design for an ultra-high Q photonic crystal nanocavity engineered to interact with nitrogen-vacancy (NV) centers located near the surface of a single crystal diamond sample is presented. The structure is based upon a nanowire photonic crystal geometry, and consists of a patterned high refractive index thin film, such as gallium phosphide (GaP), supported by a diamond substrate. The nanocavity supports a mode with quality factor Q > 1.5 x 10(6) and mode volume V < 0.52(lambda/nGaP)(3), and promises to allow Purcell enhanced collection of spontaneous emission from an NV located more than 50 nm below the diamond surface. The nanowire photonic crystal waveguide can be used to efficiently couple light into and out of the cavity, or as an efficient broadband collector of NV phonon sideband emission. The proposed structures can be fabricated using existing materials and processing techniques.

Van der Waals engineering of ferromagnetic semiconductor heterostructures for spin and valleytronics

A van der Waals heterostructure of monolayer WSe2 and ferromagnetic CrI3 enables exceptional control of valley pseudospin. The integration of magnetic material with semiconductors has been fertile ground for fundamental science as well as of great practical interest toward the seamless integration of information processing and storage. We create van der Waals heterostructures formed by an ultrathin ferromagnetic semiconductor CrI3 and a monolayer of WSe2. We observe unprecedented control of the spin and valley pseudospin in WSe2, where we detect a large magnetic exchange field of nearly 13 T and rapid switching of the WSe2 valley splitting and polarization via flipping of the CrI3 magnetization. The WSe2 photoluminescence intensity strongly depends on the relative alignment between photoexcited spins in WSe2 and the CrI3 magnetization, because of ultrafast spin-dependent charge hopping across the heterostructure interface. The photoluminescence detection of valley pseudospin provides a simple and sensitive method to probe the intriguing domain dynamics in the ultrathin magnet, as well as the rich spin interactions within the heterostructure.