Readout and control of a single nuclear spin with a metastable electron spin ancilla

Abstract

Electron and nuclear spins associated with point defects in insulators are promising systems for solid state quantum technology [1][2][3] . While the electron spin usually is used for readout and addressing, nuclear spins are exquisite quantum bits 4,5 and memory systems 3,6 . With these systems single-shot readout of nearby nuclear spins 5 as well as entanglement 4,7,8 aided by the electron spin has been shown. While the electron spin in this example is essential for readout it usually limits nuclear spin coherence 9. This has set of the quest for defects with spin-free ground states 8,10 . Here, we isolate a hitherto unidentified defect in diamond and use it at room temperature to demonstrate optical spin polarization and readout with exceptionally high contrast (up to 45%), coherent manipulation of an individual excited triplet state spin, and coherent nuclear spin manipulation using the triplet electron spin as a meta-stable ancilla. By this we demonstrate nuclear magnetic resonance and Rabi oscillations of the uncoupled nuclear spin in the spin-free electronic ground state. Our study demonstrates that nuclei coupled to single metastable electron spins are useful quantum systems with long memory times despite electronic relaxation processes.Coupled electron and nuclear spins in solids are promising candidates for quantum memories and registers and present a particular class in the emerging field of hybrid quantum systems 7,[11][12][13][14] , in which different types of qubits perform distinct functions according to their advantageous properties. In this particular case, the nuclear spin, which is weakly coupled to the environment, serves as a long-lived arXiv:1302.4608v1 [quant-ph] 19 Feb 2013 quantum memory, whereas the electron spin, which has a short coherence time, but interacts strongly with external fields, serves as a readout gate 4,7,9 . In this architecture, the permanent presence of the electron spin is a source of decoherence to the nuclear spin 8 . To avoid such electron spin induced decoherence, the electron that carries the spin should be physically removed when it is not needed and returned to the nuclear spin only when the initialization or readout gate is applied. One approach to address this problem is to frequently remove the electron, e.g. by photo-ionization with a strong laser, resulting in a motional narrowing type of decoupling 9 . Another approach -that is followed in this workis to choose an electronic system with a spin-free ground state and a meta-stable excited spin state that can be optically pumped and activated prior to the application of the readout gate 8 . Such a system implemented with a single solid state defect would enable a universal nuclear spin gate. In the following we present a suitable defect in diamond and demonstrate coherent control of a single nuclear spin in the spin-free electronic ground state. Notably, besides the NV center, this is the second known single spin defect in the solid state, whose coherent spin motion is detectable at room temperature....

Characterization of oxygen defects in diamond by means of density functional theory calculations

“…and it may be employed as a qubit similar to the ST1 center in diamond 57 . Therefore, we study the shelving and excited states of O S (0) in detail.…”

Universal control and error correction in multi-qubit spin registers in diamond

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Quantum registers of nuclear spins coupled to electron spins of individual solid-state defects are a promising platform for quantum information processing [1][2][3][4][5][6][7][8][9][10][11][12][13]. Pioneering experiments selected defects with favourably located nuclear spins having particularly strong hyperfine couplings [4][5][6][7][8][9][10].

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“…These results provide multiple qubits per defect with high certainty and are compatible with control of the intrinsic nitrogen spin and potential strongly coupled 13 C spins. Our techniques can be applied to a wide variety of other electron-nuclear spin systems [2,3,10,13]. The resulting reliable multi-qubit registers can be combined with recently demonstrated coherent coupling between (distant) electron spins [11,18] to realize novel surface-code quantum-computation architectures that use four qubits per defect node [19] and extended quantum networks for long-distance quantum communication.…”

Optical signatures of silicon-vacancy spins in diamond

“…Recent studies of such centres include chromium- 17,18 , xenon- 19 nickel- 20 and possibly oxygen-related centres 21 , as well as the negatively charged silicon-vacancy (SiV) centre [22][23][24] . The latter has the advantage of being the brightest reported colour centre in diamond 24 .…”