Single-Qubit Operations with the Nitrogen-Vacancy Center in Diamond

Abstract

A concept combining optics and microwave pulses with the negative charge-state of the nitrogenvacancy (NV --) center in diamond is demonstrated through experiments that are equivalent to single-qubit gates, and decoherence for this qubit is examined. The spin levels of the ground state provide the two-level system. Optical excitation provides polarization of these states. The polarized state is operated coherently by 35 GHz microwave pulses. The final state is read out through the photoluminescence intensity. Decoherence arises from different sources for different samples. For high-pressure, high-temperature synthetic diamonds, the high concentration of substitutional N limits the phase-memory to a few ms. In a single-crystal CVD diamond, the phase memory time is at least 32 ms at 100 K. 14 N is tightly coupled to the electronic spin and produces modulation of the electron-spin echo decay under certain conditions. A two-qubit gate is proposed using this nuclear spin. This demonstration provides a great deal of insight into quantum devices in the solid state with some possibility for real application. IntroductionThe nitrogen-vacancy center in its negative charge-state (NV --) in diamond is a defect/host system with remarkable properties. Its optical transition and spin were established through optical studies and EPR [1,2]. A long spin lifetime and more details of the energy levels were obtained through Optically Detected Magnetic Resonance (ODMR) and Raman heterodyne spectroscopy at zero and small magnetic fields [3,4]. These studies and others confirmed that the center has a strong optical transition and a long-lived spin with S ¼ 1 in the ground state. Many further experiments have been performed including room temperature ODMR of single NV --centers [5].The strong optical transition, long spin lifetimes, and stability of NV --in diamond have led naturally to concepts and demonstrations aimed at quantum information technology. One approach employs the 13 C nuclear spins as qubits with radio-frequency pulses as gates to implement a quantum computer [6]. A second approach makes use of cavity dark states for quantum computing [7]. Other works use the NV --center as a single-photon source for application in quantum communication [8,9].In this work, a concept is demonstrated that uses the electronic spin of the NV --in diamond as the qubit with optical polarization, microwave pulses as operators, and optical emission for readout. Gates involving a single qubit are demonstrated with ensembles of NV --centers. Previous work with one sample [10] has been extended to a set of samples, and some of the causes of decoherence can now be given. The involvement of

Detecting the presence of weak magnetic fields using nitrogen-vacancy centers

“…Such a unitary operator can be implemented experimentally for nitrogen-vacancy centers [54]. To sum up, in this case, we first allow the nitrogenvacancy center to interact with the magnetic field, apply the operator U R to the nitrogen-vacancy center state, and then perform the measurement in the {|0 ,|1 } basis.…”

Optical spin polarisation of the N-V centre in diamond

“…However, if polarisation occurred by a two-photon process, such as that suggested in Ref. [12], the strength of the EPR signal would be expected to increase quadratically with optical pumping power. We measured the strength of the EPR signal for laser powers in the 100-850 mW range (measured at the laser output).…”

Electrical detection of coherent 31P spin quantum states

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In recent years, a variety of solid-state qubits has been realized, including quantum dots [1,2], superconducting tunnel junctions [3,4] and point defects [5,6]. Due to its potential compatibility with existing microelectronics, the proposal by Kane [7,8] based on phosphorus donors in Si has also been pursued intensively [9,10,11].

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