93,200 research outputs found
Robust quantum-network memory using decoherence-protected subspaces of nuclear spins
The realization of a network of quantum registers is an outstanding challenge
in quantum science and technology. We experimentally investigate a network node
that consists of a single nitrogen-vacancy (NV) center electronic spin
hyperfine-coupled to nearby nuclear spins. We demonstrate individual control
and readout of five nuclear spin qubits within one node. We then characterize
the storage of quantum superpositions in individual nuclear spins under
repeated application of a probabilistic optical inter-node entangling protocol.
We find that the storage fidelity is limited by dephasing during the electronic
spin reset after failed attempts. By encoding quantum states into a
decoherence-protected subspace of two nuclear spins we show that quantum
coherence can be maintained for over 1000 repetitions of the remote entangling
protocol. These results and insights pave the way towards remote entanglement
purification and the realisation of a quantum repeater using NV center quantum
network nodes
Stabilisation of Quantum Computations by Symmetrisation
We propose a method for the stabilisation of quantum computations (including
quantum state storage). The method is based on the operation of projection into
, the symmetric subspace of the full state space of redundant
copies of the computer. We describe an efficient algorithm and quantum network
effecting --projection and discuss the stabilising effect of the
proposed method in the context of unitary errors generated by hardware
imprecision, and nonunitary errors arising from external environmental
interaction. Finally, limitations of the method are discussed.Comment: 20 pages LaTeX, 2 postscript figure
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