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Register a new userEntanglement of dark electron-nuclear spin defects in diamond
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A promising approach for multi-qubit quantum registers is to use optically addressable spins to control multiple dark electron-spin defects in the environment. While recent experiments have observed signatures of coherent interactions with such dark spins, it is an open challenge to realize the individual control required for quantum information processing. Here we demonstrate the initialisation, control and entanglement of individual dark spins associated to multiple P1 centers, which are part of a spin bath surrounding a nitrogen-vacancy center in diamond. We realize projective measurements to prepare the multiple degrees of freedom of P1 centers - their Jahn-Teller axis, nuclear spin and charge state - and exploit these to selectively access multiple P1s in the bath. We develop control and single-shot readout of the nuclear and electron spin, and use this to demonstrate an entangled state of two P1 centers. These results provide a proof-of-principle towards using dark electron-nuclear spin defects as qubits for quantum sensing, computation and networks.
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We demonstrate operation of a rotation sensor based on the $^{14}$N nuclear spins intrinsic to nitrogen-vacancy (NV) color centers in diamond. The sensor employs optical polarization and readout of the nuclei and a radio-frequency double-quantum pulse protocol that monitors $^{14}$N nuclear spin precession. This measurement protocol suppresses the sensitivity to temperature variations in the $^{14}$N quadrupole splitting, and it does not require microwave pulses resonant with the NV electron spin transitions. The device was tested on a rotation platform and demonstrated a sensitivity of 4.7 $^{circ}/sqrt{rm{s}}$ (13 mHz/$sqrt{rm{Hz}}$), with bias stability of 0.4 $^{circ}$/s (1.1 mHz).
Atomic-size spin defects in solids are unique quantum systems. Most applications require nanometer positioning accuracy, which is typically achieved by low energy ion implantation. So far, a drawback of this technique is the significant residual implantation-induced damage to the lattice, which strongly degrades the performance of spins in quantum applications. In this letter we show that the charge state of implantation-induced defects drastically influences the formation of lattice defects during thermal annealing. We demonstrate that charging of vacancies localized at e.g. individual nitrogen implantation sites suppresses the formation of vacancy complexes, resulting in a tenfold-improved spin coherence time of single nitrogen-vacancy (NV) centers in diamond. This has been achieved by confining implantation defects into the space charge layer of free carriers generated by a nanometer-thin boron-doped diamond structure. Besides, a twofold-improved yield of formation of NV centers is observed. By combining these results with numerical calculations, we arrive at a quantitative understanding of the formation and dynamics of the implanted spin defects. The presented results pave the way for improved engineering of diamond spin defect quantum devices and other solid-state quantum systems.
The emerging field of quantum acoustics explores interactions between acoustic waves and artificial atoms and their applications in quantum information processing. In this experimental study, we demonstrate the coupling between a surface acoustic wave (SAW) and an electron spin in diamond by taking advantage of the strong strain coupling of the excited states of a nitrogen vacancy center, while avoiding the short lifetime of these states. The SAW-spin coupling takes place through a lamda-type three-level system where two ground spin states couple to a common excited state through a phonon-assisted as well as a direct dipole optical transition. Both coherent population trapping and optically-driven spin transitions have been realized. The coherent population trapping demonstrates the coupling between a SAW and an electron spin coherence through a dark state. The optically-driven spin transitions, which resemble the sideband transitions in a trapped ion system, can enable the quantum control of both spin and mechanical degrees of freedom and potentially a trapped-ion-like solid state system for applications in quantum computing. These results establish an experimental platform for spin-based quantum acoustic, bridging the gap between spintronics and quantum acoustics.
We experimentally investigate the protection of electron spin coherence of nitrogen vacancy (NV) center in diamond by dynamical nuclear polarization. The electron spin decoherence of an NV center is caused by the magnetic ield fluctuation of the $^{13}$C nuclear spin bath, which contributes large thermal fluctuation to the center electron spin when it is in equilibrium state at room temperature. To address this issue, we continuously transfer the angular momentum from electron spin to nuclear spins, and pump the nuclear spin bath to a polarized state under Hartman-Hahn condition. The bath polarization effect is verified by the observation of prolongation of the electron spin coherence time ($T_2^*$). Optimal conditions for the dynamical nuclear polarization (DNP) process, including the pumping pulse duration and depolarization effect of laser pulses, are studied. Our experimental results provide strong support for quantum information processing and quantum simulation using polarized nuclear spin bath in solid state systems.
We present systematic measurements of longitudinal relaxation rates ($1/T_1$) of spin polarization in the ground state of the nitrogen-vacancy (NV$^-$) color center in synthetic diamond as a function of NV$^-$ concentration and magnetic field $B$. NV$^-$ centers were created by irradiating a Type 1b single-crystal diamond along the [100] axis with 200 keV electrons from a transmission electron microscope with varying doses to achieve spots of different NV$^-$ center concentrations. Values of ($1/T_1$) were measured for each spot as a function of $B$.
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