Protecting a Diamond Quantum Memory by Charge State Control

Abstract

In recent years, solid-state spin systems have emerged as promising candidates for quantum information processing (QIP). Prominent examples are the nitrogen-vacancy (NV) center in diamond [1][2][3], phosphorous dopants in silicon (Si:P) [4][5][6], rare-earth ions in solids [7][8][9] and VSi-centers in silicon-carbide (SiC) [10][11][12]. The Si:P system has demonstrated that its nuclear spins can yield exceedingly long spin coherence times by eliminating the electron spin of the dopant. For NV centers, however, a proper charge state for storage of nuclear spin qubit coherence has not been identified yet [13]. Here, we identify and characterize the positively-charged NV center as an electron-spin-less and optically inactive state by utilizing the nuclear spin qubit as a probe [13]. We control the electronic charge and spin utilizing nanometer scale gate electrodes. We achieve a lengthening of the nuclear spin coherence times by a factor of 20. Surprisingly, the new charge state allows switching the optical response of single nodes facilitating full individual addressability.Spin defects are excellent quantum systems. Particularly, defects that possess an electron spin together with a set of well-defined nuclear spins make up excellent, small quantum registers [3,14]. They have been used for demonstrations in quantum information processing [3,15], long distance entanglement [16] and sensing [17]. In such systems the electron spin is used for efficient readout (sensing or interaction with photons) whereas the nuclear spins are used as local quantum bits. Owing to their different magnetic and orbital angular momentum, electron and nuclear spins exhibit orders of magnitude different spin relaxation times. As an example, NV electron spins typically relax on a timescale of ms under ambient conditions [18], while nuclear spins do have at least minutes-long spin relaxation times [19]. However, the hyperfine coupling of nuclear spins to the fast relaxing electron spins in most cases significantly deteriorates the nuclear spin coherence, and eventually its relaxation time, down to time scales similar to the electron spin. For NV centers at room-temperature, this limits coherence times to about 10 ms [17,19,20]. For other hybrid spin ensembles e.g. in Si:P, this strict limit was overcome by ionizing the electron spin donors and thereby removing the electron spin. The resulting T 2 times were on the order of minutes for Si:P ensembles [5] and less than a second for single spins [6,21].It is known that the NV center in diamond exists in various charge states. Besides the widely employed negative charge state (NV − ), it is known to have a stable NV 0 and eventually NV + configurations. NV − has a spin triplet ground state with total spin angular momentum S = 1. Calculations as well as spectroscopic data suggest that the NV 0 ground state is S = 1/2 while NV + is believed to be S = 0, i.e. diamagnetic. Several experiments have demonstrated the optical ionization from NV − to the neutral NV 0 charge-state [13,[22][23][24][25][26...

All-optical hyperpolarization of electron and nuclear spins in diamond

“…4). The spin lifetimes of nuclei in strongly-hyperfine-coupled paramagnetic systems are typically limited by the lifetime of the associated electron: nuclear-spin lifetimes have been extended in silicon and diamond by actively "removing" the unpaired electron from such a system for a given duration, then returning it for readout via the electron [41,42]. We therefore interpret our effective nuclear T 1 in terms of a highly polarized population of N s + , which is nonparamagnetic and therefore can sustain long nuclear-spin lifetimes.…”

Selective measurement of charge dynamics in an ensemble of nitrogen-vacancy centers in nanodiamond and bulk diamond

“…Therefore, controlling the charge state of the NV centers is crucial. A stable and well-controlled NV charge state not only improves the sensitivity of detection, but also leads to applications such as sensing of electrochemical potentials [11], and enhanced nuclear spin coherence time [12].…”

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

“…Spin qubits associated with color centers in diamond lie somewhere at the middle of these two extremes, rendering these qubits compelling systems for various applications including quantum memory construction, nuclear spin addressing, and nanoscale sensing of magnetism, proteins, and chemicals . These remarkable achievements, in turn, justify the advantages of diamond as host material for spin qubits: the wide bandgap of diamond allows the formation of deep impurity levels by the defects, and the well separation from the band edges effectively reduces the number of channels for spin decay.…”