Diamond Spins Shining Bright

Abstract

The silicon-vacancy (SiV − ) color center in diamond has attracted attention because of its unique optical properties. It exhibits spectral stability and indistinguishability that facilitate efficient generation of photons capable of demonstrating quantum interference. Here we show optical initialization and readout of electronic spin in a single SiV − center with a spin relaxation time of T 1 ¼ 2.4 AE 0.2 ms. Coherent population trapping (CPT) is used to demonstrate coherent preparation of dark superposition states with a spin coherence time of T ⋆ 2 ¼ 35 AE 3 ns. This is fundamentally limited by orbital relaxation, and an understanding of this process opens the way to extend coherence by engineering interactions with phonons. Hyperfine structure is observed in CPT measurements with the 29 Si isotope which allows access to nuclear spin. These results establish the SiV − center as a solid-state spin-photon interface. DOI: 10.1103/PhysRevLett.113.263602 PACS numbers: 42.50.Gy, 03.67.Lx, 42.50.Ex, 61.72.jn Coherent quantum systems which efficiently couple long-lived quantum memories to optical photons are a key resource for realizing quantum networks [1]. Color centers in diamond [2] are attractive candidates owing to unique properties of diamond, which include optical transparency and a high lattice quality that allows spin to function as long-lived quantum memory [3]. The negative silicon-vacancy (SiV − ) defect in diamond [4-6] has exceptional optical properties that facilitate efficient generation of indistinguishable photons from multiple distinct emitters [7]. Here we show optical initialization and readout of electronic spin in a single SiV − center with a spin relaxation time of T 1 ¼ 2.4 AE 0.2 ms. Two-photon resonance [8] is used to demonstrate coherent preparation of dark superposition states with a spin coherence time of T ⋆ 2 ¼ 35 AE 3 ns. This is shown to be limited by orbital relaxation that may be suppressed by engineering interactions with phonons. We present the first evidence of hyperfine interaction with a 29 Si nuclear spin in SiV − which can potentially be used as a memory qubit [9].Quantum information processing efforts in diamond have mainly focused on the nitrogen-vacancy (NV − ) center because of its excellent spin properties at ambient conditions [10]. All-optical access to NV − spin is possible [11][12][13][14]; however, its large phonon sideband and spectral diffusion reduce coherent photon generation rates and limit the development of NV − quantum networks [15][16][17]. The main optical advantage provided by the SiV − center is that 70% of its fluorescence is concentrated in a sharp zero-phonon line (ZPL), making it ideal for single photon source applications [18,19]. It is spectrally stable at 737 nm, exhibits line widths limited by the excited state lifetime [20], and can be coupled to optical cavities [21,22]. Physically, the SiV − center consists of a single silicon atom replacing two carbon atoms in the diamond lattice, forming D 3d symmetry as illustrated in Fig. 1(a) [4][5]...

Building Blocks for Quantum Network Based on Group‐IV Split‐Vacancy Centers in Diamond

“…[165] One possible solution is to use the electron spin within XV − color center as the photonic interface to gate the interaction between nucleus and photons, such that when the gate is on, the nuclear spin can be easily controlled via external fields, while when the gate is off, information stored in a nucleus enjoy the long coherence time granted by this exquisite qubit. [15,16,19] Previously, such hybrid quantum system has been realized on 15 N nuclear spins coupled to a single NV − center, where level anticrossing and optical pumping are used to polarize 15 N nuclei to an effective temperature of K. [166] Later on, qubit formed by a single 13 C nucleus in the vicinity of an NV − center, [16,167] or next to an ST1 center [168] is also demonstrated. Recently, Metsch et al [169] show that SiV − center can also be used as a sensitive probe to initialize and read out the nuclear spin of a nearby 13 C atom that dynamically couples to the SiV − electron via Hartmann-Hahn double resonance.…”

“…Recently, Metsch et al [169] show that SiV − center can also be used as a sensitive probe to initialize and read out the nuclear spin of a nearby 13 C atom that dynamically couples to the SiV − electron via Hartmann-Hahn double resonance. [170] By carefully matching the Rabi frequency of electron spin (driven by a resonant microwave) to the Larmor frequency of 13 C nucleus (defined by external magnetic field), cross-relaxation between the two spin species can be initiated, empowering a coherent transfer of spin polarization from electron to 13 C, as shown in Figure 5b. After a repetitive application of this transferring process, a maximum polarization of 60% on nuclear spin is demonstrated, limited by the electron spin decay during each polarization loop.…”

“…After a repetitive application of this transferring process, a maximum polarization of 60% on nuclear spin is demonstrated, limited by the electron spin decay during each polarization loop. Together with a direct control of 13 C nuclear spin by using resonant radio-frequency (RF) waves, a coherence time of T nuc 2 = 6.8 ms is determined via spin-echo experiment, limited by electron spin flipping rate during spinlattice relaxation process, as shown in Figure 5d.…”

“…On the other hand, strong interaction with the controlling field (such as light field, micro‐, and radiowave) is needed to boost the operation speed and lower the power consumption of the operation. Eventually, a tradeoff has to be made between coherence time and operation speed for each system . For example, trapped ions possess an exceptionally long coherence time , approaching minute timescale thanks to the outstanding isolation of the qubits from the noisy environment, but maneuvering these qubits is a slow process.…”

“…Eventually, a tradeoff has to be made between coherence time and operation speed for each system. [13] For example, trapped ions possess an exceptionally long coherence time T ⋆ 2 , approaching minute timescale [3] thanks to the outstanding isolation of the qubits from the noisy environment, but maneuvering these qubits is a slow process. In contrast, electron spin confined in a semiconductor quantum dot can be optically or electrically rotated within tens of picoseconds, but its coherence time is no more than a few microseconds, limited by the interaction with the nuclear spin bath of the host material.…”