Diamond Materials

Diamond Materials for Quantum Application

23. September 2014: The DFG research group FOR 1493 “Diamond Materials and Quantum Applications” goes into its second funding period. FOR1493 is a national research consortium funded by the Deutsche Forsch-ungsgemeinschaft.

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ERC Advanced Grant


A new color center in diamond and its application:

Initialization and readout of a single nuclear spin with a meta-stable electron spin ancilla

Electron spins in solids have been considered as one of promising candidates for solid state quantum qubit because their spin states can be well detected – even on the single spin level – either electrically or optically owing to their abilities to strongly interact with electrical charges and optical photons. Because the initialization and readout process can limit the coherence of such delicate quantum object, hybrid quantum systems consisting of electron and nuclear spins have been proposed. While the electron spins usually are used for readout, the quantum information can be stored in the nuclear spins which usually have longer coherence time.

The coupling between electron and nuclear spins in this hybrid quantum system is essential for readout and transfer of quantum information. It can, however, meditate the electron-nuclear spin flip-flops which also limits nuclear spin coherence. This has motivated searching for new spin systems in which the nuclear spins can be decoupled during the storage process. A spin system which has a spin-free ground state can be a favorable one [1].

For our study, a newly found color center in diamond nano-wires, the ST1 center, has been used. This new color center has an electronic singlet ground state and a meta-stable triplet state and shows exceptionally high (up to 45 %) optical spin signal contrast. The strong coupling between the metastable electron spin and a nearby nuclear spin is used for the initialization of the nuclear spin memory which is then stored for at least 1 ms at room temperature, while the electronic spin decays to the singlet ground state [2]. Even though the memory time is currently limited by either intrinsic nuclear spin bath decoherence or paramagnetic impurities in nano-wires, this study demonstrates that nuclear spins coupled to single metastable electron spins are useful quantum systems with potentially long memory times.

Left: An illustrative image showing diamond nano-wires coupled to green Laser light, middle: Optically detected resonance transitions of a metastable electronic triplet spin of a single ST1 center coupled to a 13C nuclear spin. Some transitions get weaker because of the optical nuclear polarization induced by the level anti-crossing around 42 mT, right: the observed nuclear spin Rabi oscillation at dark condition.

[1] V. Filidou et al., Nat. Phys 8, 596 (2012).
[2] S.-Y. Lee et al., arXiv:1302.4608 (2013), to be published in Nat. Nano.