Nitrogen-Vacancy Centers in Diamond
NV centers are atomic defects in diamond whose electron spin is a qubit readable by light and stable at room temperature.
A defect as a qubit
A nitrogen-vacancy center is a point defect in diamond where a nitrogen atom replaces a carbon and sits next to a missing carbon (a vacancy). The negatively charged NV center has an electron spin ground state that acts as a qubit. Remarkably, it retains useful spin coherence even at room temperature, unusual among qubit modalities.
Optical control and readout
The NV center can be initialized and read out optically: green laser light pumps it into a known spin state, and the red fluorescence it emits is brighter for one spin projection than the other, giving a direct optical readout. Microwave pulses drive spin rotations for single-qubit gates. Nearby carbon-13 nuclear spins provide additional long-lived quantum memory registers.
Uses
- Quantum sensing of magnetic and electric fields, temperature, and strain at nanometer scale
- Quantum network nodes, because the spin can emit entangled photons
- Small quantum registers combining the electron spin with nuclear spins
Coherence and limits
In isotopically purified diamond, NV electron-spin coherence can reach milliseconds; coupled nuclear spins last far longer. The obstacles to large processors are placing many NV centers precisely, coupling distant centers, and the modest photon collection efficiency that slows optical entanglement between nodes.
NV centers are less a route to a large monolithic processor than a strong platform for sensing and for the nodes of a quantum network, where room-temperature operation and a clean spin-photon interface are decisive advantages.