Abstract
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 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 internode 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 realization of a quantum repeater using nitrogen-vacancy center quantum-network nodes.Received 9 March 2016DOI:https://doi.org/10.1103/PhysRevX.6.021040This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasOpen quantum systems & decoherenceQuantum memoriesPhysical SystemsNitrogen vacancy centers in diamondQuantum Information
Highlights
Linking multiqubit nodes into a large-scale quantum network [1,2,3,4] will open up exciting opportunities ranging from fundamental tests [5] and enhanced timekeeping [6] to applications in quantum computing and cryptography [1,7,8,9]
This dephasing can be mitigated by a suited dynamical decoupling sequence [33], which is inherent in the BarrettKok entangling sequence [Fig. 1(c)]: for τ 1⁄4 0, the time interval between the microwave (MW) π=2 pulse and the MW π pulse has the same duration as the time interval between the MW π pulse and the start of the electronic spin reset
We study a prototype quantum-network node consisting of nuclear spin qubits hyperfine coupled to an optically active electronic spin in a diamond with natural isotope abundance
Summary
Linking multiqubit nodes into a large-scale quantum network [1,2,3,4] will open up exciting opportunities ranging from fundamental tests [5] and enhanced timekeeping [6] to applications in quantum computing and cryptography [1,7,8,9]. Pioneering experiments with atomic ensembles [3], single atoms trapped in vacuum [2,4,10,11], and spins in solids [12,13,14] have demonstrated entanglement between two optically connected nodes Extending these schemes to quantum networks involving many nodes and spanning large distances is hindered by unavoidable imperfections, including photon loss and local control errors, which cause the success probability and entanglement fidelity to decay rapidly both with the number of nodes and with distance. We use decoherenceprotected subspaces (DPSs) to enhance the robustness of quantum state storage, which enables us to increase the exponential decay constant of the qubit fidelity above 1000 repetitions of the internode entangling sequence
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