High-fidelity projective read-out of a solid-state spin quantum register

Abstract

Initialization and read-out of coupled quantum systems are essential ingredients for the implementation of quantum algorithms. Single-shot read-out of the state of a multi-quantum-bit (multi-qubit) register would allow direct investigation of quantum correlations (entanglement), and would give access to further key resources such as quantum error correction and deterministic quantum teleportation. Although spins in solids are attractive candidates for scalable quantum information processing, their single-shot detection has been achieved only for isolated qubits. Here we demonstrate the preparation and measurement of a multi-spin quantum register in a low-temperature solid-state system by implementing resonant optical excitation techniques originally developed in atomic physics. We achieve high-fidelity read-out of the electronic spin associated with a single nitrogen-vacancy centre in diamond, and use this read-out to project up to three nearby nuclear spin qubits onto a well-defined state. Conversely, we can distinguish the state of the nuclear spins in a single shot by mapping it onto, and subsequently measuring, the electronic spin. Finally, we show compatibility with qubit control: we demonstrate initialization, coherent manipulation and single-shot read-out in a single experiment on a two-qubit register, using techniques suitable for extension to larger registers. These results pave the way for a test of Bell's inequalities on solid-state spins and the implementation of measurement-based quantum information protocols.

Maximizing the purity of a qubit evolving in an anisotropic environment

“…The procedure described here can be used to predict an optimal state in which to store an ancilla. This may be useful in other systems with anisotropic interactions, including nitrogen-vacancy (NV) centers in diamond, 13 or phosphorus donors in silicon, 14 where the high-fidelity preparation of electron-spin ancillas is important for nuclear-spin readout.…”

“…This topic has become especially interesting in the context of spin-bath dynamics. [17][18][19][20] For slowly-evolving nuclear-spin baths, it is indeed possible to approach pure-state initial conditions through algorithmic cooling [9][10][11] or direct measurement of the bath state, 13,[21][22][23][24][25] so studying the purity for these systems is especially important from both a practical and a fundamental point of view.…”

Dual-channel lock-in magnetometer with a single spin in diamond

“…Recent improvements in these factors, e.g. through photonic nanostructures 12,41 or resonant excitation 46 can result in decreasing R → 1, while increasing the measurement time t M ≈ 20 µ sec. Correspondingly our time constant can thus be reduced by almost three orders of magnitude.…”

Nanoscale nuclear magnetic imaging with chemical contrast

“…In future, two attractive extensions appear realistic. First, improved readout techniques for the NV sensor promise to accelerate acquisition by three orders of magnitude down to a speed of 20 milliseconds/pixel by using advanced spin readout techniques 24 or nuclear quantum memories 25 . Second, exploiting advanced NMR techniques will provide a much greater variety of contrast mechanisms than simple isotope-labeling used in this study.…”