Photonic crystal defect cavities coupled to N-V centres in diamond
Luca Marseglia, J. P. Harrison, John Patrick Hadden, A. B. Young, Fedor Jelezko, Boris Naydenov, Jan Meijer, A. C. Stanley‐Clarke, Y.-L. D. Ho, Jeremy L. O’Brien, John Rarity
We use focused ion beam (FIB) etching to create suspended photonic crystal cavities in diamond. Our goal is to enhance and control the spontaneous emission of single N-V colour centres, which act like single `two-level atoms' emitting single photons. The single nitrogen-vacancy (N-V) colour centre in diamond has attracted a lot of interest because it can be optically addressed, is photostable at room temperature and has a paramagnetic ground state whose spin can be initialized and read-out optically. By enclosing the (N-V) colour centre in a resonant cavity we aim to develop rapid readout of this optically addressable single spin. We show a technique using FIB and confocal microscopy to locate single N-V centres and discuss progress towards etching cavities around single centres.
We use focused ion beam (FIB) etching to create suspended photonic crystal cavities in diamond. Our goal is to enhance and control the spontaneous emission of single N-V colour centres, which act like single `two-level atoms' emitting single photons. The single nitrogen-vacancy (N-V) colour centre in diamond has attracted a lot of interest because it can be optically addressed, is photostable at room temperature and has a paramagnetic ground state whose spin can be initialized and read-out optically. By enclosing the (N-V) colour centre in a resonant cavity we aim to develop rapid readout of this optically addressable single spin. We show a technique using FIB and confocal microscopy to locate single N-V centres and discuss progress towards etching cavities around single centres.
The nitrogen-vacancy (N-V) defect in ultra-pure diamond shows great promise for the implementation of qubits for quantum computing. The N-V defect is a three level system which behaves as an efficient room temperature source of single photons at a wavelength of 637 nm. The N-V centre ground state spin strongly modulates the rate of spontaneous emission providing a mechanism for spin read out. Recently, it is shown that spin-readout with the minimum number of photons can be achieved by efficiently coupling light to the transition in a sub- wavelength scale micro-cavity. The aim of this paper is to place the N-V centre into a cavity at the centre of a suspended slab photonic crystal structure made from hexagonal array of cylindrical air holes. The light is confined by distributed Bragg reflection in the plane of periodicity (xy) and by total internal reflection in the perpendicular plane (z). The work consists of both modelling the photonic crystal to optimise the parameters and fabricating the structures using focussed ion beam milling.
In this work we aim to exploit one of the most studied defect color centers in diamond , the negatively charged nitrogen vacancy (NV -) color center, a three level system which emits a single photon at a wavelength of 637nm providing a possible deterministic single photon emitter very useful for quantum computing applications.Moreover the possibility of placing aNV -in a photonic crystal cavity will enhance the coupling between photons and NV -center.This could also allow us to address the ground state of the NV -center, whose spin, could be used as qubit.It is also remarkable to notice that for quantum computing purposes it is very useful to increase the light collection from the NV -centers, and in order to do that we performed a study of another structure, the solid immersion lens, which consists of an hemisphere whose center is at the position of an emitter, in this case the NV -center, increasing the collection of the light from it.In order to create these structures we used a method called focused ion beam which allowed us to etch directly into the diamond many different kinds of structures.In order to allow an interaction between these structures and the NV -centers we need to have a method to locate the NV -center precisely under the etched structures.We developed a new technique (Marseglia et al. (2011)) where we show how to mark a single NV -center and how to etch a desired structure over it on demand.This technique gave very good results allowing us to etch a solid immersion lens onto a NV -previously located and characterized, increasing the light collection from the NV -of a factor of 8×.
Single negatively charged nitrogen-vacancy (NV-) defect centres in diamond are attractive systems for the implementation of solid state quantum information processing (QIP) and quantum key distribution (QKD). In both approaches, the coupling of an individual NV-centre to a resonant microcavity is of interest: it would improve the optical readout of the NV-centre electron spin state in QIP and enhance the collection efficiency of the single photon fluorescence in QKD while increasing the coherence length of the emission. We theoretically demonstrate that, at room temperature, the coupling to a single-mode Fabry-Perot microcavity can be used to obtain a fluorescence spectrum narrowing without loss of total intensity. We also experimentally demonstrate the control of the fluorescence spectrum of a single NV-centre by adjusting the thickness of the microcavity. Finally, we report a doubling of the emission spectral density with respect to the single mirror configuration.
Nitrogen-vacancy (NV) centers feature outstanding properties such as a spin coherence time of up to 1 s as well as a level structure offering the possibility to initialize, coherently manipulate, and optically read-out the spin degree of freedom of the ground state. However, only about 3% of their photon emission is channeled into the zero phonon line (ZPL), limiting both the rate of indistinguishable single photons and the signal-to-noise ratio (SNR) of coherent spin-photon interfaces. We here report on the enhancement of the SNR of the optical spin read-out achieved by tuning the mode of a two-dimensional photonic crystal (PhC) cavity into resonance with the NV-ZPL. PhC cavities are fabricated by focused ion beam milling in thin reactive ion etched ultrapure single crystal diamond membranes featuring modes with Q-factors of up to 8250 at mode volumes below one cubic wavelength. NV centers are produced in the cavities in a controlled fashion by a high resolution atomic force microscope implantation technique. On cavity resonance, we observe a lifetime shortening from 9.0 ns to 8.0 ns as well as an enhancement of the ZPL emission by almost one order of magnitude. Although on resonance the collection efficiency of ZPL photons and the spin-dependent fluorescence contrast are reduced, the SNR of the optical spin read-out is almost tripled for the cavity-coupled NV centers.
Recently, developments in novel and high-purity materials allow for the presence of a single, solitary crystalline defect to define the electronic, magnetic, and optical functionality of a device. The discrete nature of the active dopant, whose properties are defined by a quantum mechanical description of its structure, enables radically new quantum investigations and applications in these arenas. Finally,there has been significant development in large-scale device engineering due to mature semiconductor manufacturing techniques. The diverse set of photonic device architectures offering light confinement, guiding, and extraction is a prime example. These three paradigms – solitary dopant photonics and optoelectronics (solotronics), quantum science\tand technology, and device engineering – merge in the development of novel quantum photonic devices for the next generation of information processing systems. We present in this thesis a series of investigations of optical nanostructures for single optically active spins in single crystal diamond. Chapter 1 introduces the Nitrogen-Vacancy (NV) color center, summarizes its applications, and motivates the need for their integration into photonic structures. Chapter 2 describes two prototype nanobeam photonic crystal cavities for generating strong light-matter interactions with NV centers. The first device consists of a silicon nitride photonic crystal nanobeam cavity with high quality factor \\(Q \\sim 10^5\\) and small mode volume \\(V \\sim 0.5*(\\lambda/n)^3\\). The second device consists of a monolithic diamond nanobeam cavity fabricated with the focused ion beam (FIB) directly in a single crystal diamond sample. Chapter 3 presents a high-efficiency source of single photons consisting of a single NV center in a photonic diamond nanowire. Early FIB prototypes are described, as is the first successful realization of the device achieved via reactive ion etching nanowires in a single crystal diamond containing NV centers, and finally a variation of this approach based on incorporation of NV centers in pure diamond via ion implantation. In chapter 4 we consider the optimal design of photonic devices offering both collection efficiency and cavity-enhancements and extend the model of the NV center to include photonic effects. In chapter 5 we briefly introduce a novel optically active spin discovered in a diamond nanowire. Finally, in chapter 6 we conclude with several proposals to extend this research program.
A huge variety of optical colour centres can be found in diamond, emitting in its whole wide transparency range. Although several of these centres have been demonstrated as single-photon emitters, none of them meets all of the requirements of an ideal single-photon source. In this view, we discuss the properties of prominent optical centres, such as the nitrogen vacancy, the silicon vacancy or the so-called NE8 centre, as well as recently found centres ascribed to defects containing Ni, Si, Cr and Xe. Besides suitable intrinsic properties, it is necessary for practical applications that optical centres can be created artificially on demand. Of all known methods, only ion implantation allows for the most controlled creation of such defect centres. In this paper, we discuss how nanoscalability, that is, the nanometre placement and the deterministic creation of optical centres, can, could or cannot be achieved by the available ion implantation techniques. A fine analysis of individual optical centres is now possible, thanks to the recently developed subdiffraction optical microscopy methods.