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


Quantum error correction

Quantum error correction in a small spin-based quantum computer in diamond

Error correction is a central paradigm in classical and quantum computation. Decoherence caused by the inevitable interaction of quantum bits with their environment leads to dephasing or even relaxation. Correcting the concomitant errors thus is a fundamental requirement for scalable quantum computation. Although algorithms for error correction are known since quite some time experimental realizations are scarce. In this work we demonstrate a high degree of control sufficient for quantum error correction on a hybrid solid-spin system, based on the nitrogen-vacancy defect (NV) in diamond. Nuclear spins randomly distributed within the diamond are addressed, read out and initialized by the electron spin of the defect. The electron spin in turn is polarized and readout by optical means. Specifically, we use three nuclear spins 14 N and two
13 C as quantum bits. All nuclear spins of the register can be individually addressed via their hyperfine interaction, which allows for universal quantum control and quantum computation.

We demonstrate that joint initialization, projective readout and fast local and non-local gate operations are no conflicting requirements in such spin systems, even under ambient conditions. High-fidelity initialization of a whole spin register (99%) and single-shot readout of multiple individual nuclear spins is achieved by using the ancillary electron spin of a nitrogen-vacancy defect. Implementation of a novel non-local gate generic to our electron-nuclear quantum register allows to prepare entangled states of three nuclear spins, with fidelities exceeding 85%. With these techniques, we finally demonstrate three-qubit phase-flip error correction. Utilizing optimal control, all of the above algorithms achieve fidelities approaching fault tolerant quantum operation, thus paving the way to large scale integrations. Besides diamond spins, our techniques can be used to improve scaling of quantum networks relying on phosphorous in silicon, quantum dots, silicon carbide or rare earth ions in solids.

a Illustration of the quantum register consisting of three nuclear spins coupled to the central NV electron spin. b Reconstructed density matrix for a GHZ-like state within the three nuclear spins. c Measured process fidelity of the quantum error correction protocol, depending of the error probability.

Quantum error correction in a solid-state hybrid spin register.
G.Waldherr, Y.Wang, S. Zaiser, M. Jamali, T. Schulte-Herbrüggen, H. Abe, T. Ohshima, J. Isoya, J. F. Du, P. Neumann, J. Wrachtrup.
Nature (2014) DOI: 10.1038/nature12919