Neutral silicon vacancy (SiV0) centers in diamond are promising candidates for quantum networks because of their excellent optical properties and long spin coherence times. In this work, we present the observation of previously unreported optical transitions in SiV0 that are capable of efficiently polarizing the ground state spin. We assign groups of transitions from 825 to 890 nm to higher-lying excited states of SiV0 through a combination of optical and spin measurements. We interpret these spectroscopic lines as transitions to bound exciton states of the defect. Optical spin polarization via these bound exciton states enables the observation of optically detected magnetic resonance of SiV0.
We demonstrate optical spin polarization of the neutrally charged silicon-vacancy defect in diamond (SiV^{0}), an S=1 defect which emits with a zero-phonon line at 946 nm. The spin polarization is found to be most efficient under resonant excitation, but nonzero at below-resonant energies. We measure an ensemble spin coherence time T_{2}>100 μs at low-temperature, and a spin relaxation limit of T_{1}>25 s. Optical spin-state initialization around 946 nm allows independent initialization of SiV^{0} and NV^{-} within the same optically addressed volume, and SiV^{0} emits within the telecoms down-conversion band to 1550 nm: when combined with its high Debye-Waller factor, our initial results suggest that SiV^{0} is a promising candidate for a long-range quantum communication technology.
Neutral silicon-vacancy (
Si-V0) centers in diamond are promising candidates for quantum network applications because of their exceptional optical properties and spin coherence. However, the stabilization of
Si-V0 centers requires careful Fermi-level engineering of the diamond host material, making further technological development challenging. Here, we show that
Si-V0 centers can be efficiently stabilized by photoactivated itinerant carriers. Even in this nonequilibrium configuration, the resulting
Si-V0 centers are stable enough to allow for resonant optical excitation and optically detected magnetic resonance. Our results pave the way for on-demand generation of
Si-V0 centers as well as other emerging quantum defects in diamond.
Neutral silicon vacancy centers (SiV^{0}) in diamond are promising candidates for quantum applications; however, stabilizing SiV^{0} requires high-purity, boron-doped diamond, which is not a readily available material. Here, we demonstrate an alternative approach via chemical control of the diamond surface. We use low-damage chemical processing and annealing in a hydrogen environment to realize reversible and highly stable charge state tuning in undoped diamond. The resulting SiV^{0} centers display optically detected magnetic resonance and bulklike optical properties. Controlling the charge state tuning via surface termination offers a route for scalable technologies based on SiV^{0} centers, as well as charge state engineering of other defects.
The neutrally charged silicon vacancy in diamond is a promising system for quantum technologies that combines high-efficiency optical spin initialization with long spin lifetimes (${T}_{2}\ensuremath{\approx}1$ ms at 4 K) and up to 90% of optical emission into its 946-nm zero-phonon line. However, the electronic structure of
SiV0 is poorly understood, making further exploitation difficult. Performing photoluminescence spectroscopy of
SiV0 under uniaxial stress, we find the previous excited electronic structure of a single
3A1u state is incorrect, and identify instead a coupled $^{3}E_{u}\text{\ensuremath{-}}^{3}A_{2u}$ system, the lower state of which has forbidden optical emission at zero stress and efficiently decreases the total emission of the defect. We propose a solution employing finite strain to define a spin-photon interface scheme using
SiV0 .
Atomic defects in solids offer access to atom-like quantum properties without complex trapping methods while displaying a rich physics due to interactions with their solid-state environment. Such properties have made them an advantageous building block for quantum information processing, in particular to construct a quantum network, where information would be encoded in spins and transferred between nodes through photons. Among defects in solids, the negatively charged silicon-vacancy centre in diamond (SiV
−) has attracted attention for its very promising optical properties for such a network. In this thesis, we investigate the spin properties of the silicon-vacancy centre as a potential spin-photon interface. First, we use resonant excitation of an SiV
− centre in an external magnetic field to selectively address different electronic states and analyse the resulting fluorescence. We find evidence of selection rules in the optical transitions revealing that the centre possesses an electronic spin S = 1/2. Making use of the dependence of such selection rules on the applied magnetic field orientation, we resonantly drive two optical transitions forming a
Λ-scheme. In the double resonance condition, we achieve coherent population trapping, whereby the SiV
− is pumped into a dark state corresponding to a superposition of the two addressed ground states of opposite spin. This technique allows us to evaluate the coherence time of the dark state and hence of the spin, while demonstrating the possibility of all-optical control of the spin when a
Λ-scheme is available. We then use resonant optical pulses to initialise and read out the spin state of a single SiV
−. By tuning a microwave pulse into resonance between two ground states of opposite spin, we demonstrate optically detected magnetic resonance. Subsequently, by varying the duration of a resonant microwave pulse, we achieve coherent control of a single SiV
− electronic spin. Through Ramsey interferometry, we measure a spin dephasing time of 115
± 9 ns. We then investigate interactions of the SiV
− with its environment. We analyse the hyperfine interaction of the SiV
− spin with the nuclear spin of
29Si, with a view to taking advantage of the long-lived nuclear spin in the future. We show that single-phonon-mediated excitations between electronic states of the SiV
− are the dominant spin dephasing and population decay mechanism and evaluate how external strain alters optical selection rules and can be used to improve the coherence time of the spin.