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 2016
DOI:https://doi.org/10.1103/PhysRevX.6.021040
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Published by the American Physical Society
Physics Subject Headings (PhySH)
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Hiding a Quantum Cache in Diamonds
Published 22 June 2016
Entanglement purification, a vital enabler for practical quantum networks, has been shown to be feasible with secluded nuclear memories in diamond.
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Popular Summary
A future quantum internet that links network nodes through quantum entanglement will enable ultrasecure communication, the clustering of quantum computers, and quantum-secured computing in the cloud. In recent years, several point-to-point quantum links have been demonstrated. However, in order to realize a true quantum network, a node needs to contain robust memories that can reliably store previously established quantum entanglement while a new connection with another node is being set up. Here, we investigate the physics of one of the most promising quantum network platforms: single nuclei in a diamond lattice surrounding an electron that provides an interface to light.
Our experimental setup, which is conducted at 4 K, focuses on the individual control and readout of five nuclear spin qubits within one node. These nuclear spins have coherence times on the order of tens of milliseconds. We unravel the main limitation to the performance of such nuclear quantum memories, and we overcome this limitation by creating a novel type of memory that is composed of multiple individual nuclei prepared in special resilient quantum states.
Our results demonstrate a clear path toward the first demonstration of key quantum network protocols, thereby constituting a critical step toward a future quantum internet.