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A low-control and robust quantum refrigerator and applications with electronic spins in diamond

Mohammady, M. ; Choi, H. ; Trusheim, M. ; Bayat, A. ; Englund, D. ; Omar, Y.

Physical Review A - Atomic, Molecular, and Optical Physics Vol. 97, Nº 042124, pp. 042124-1 - 042124-16, April, 2018.

ISSN (print): 1050-2947
ISSN (online): 1094-1622

Journal Impact Factor: 2,808 (in 2014)

Digital Object Identifier: 10.1103/PhysRevA.97.042124

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We propose a general protocol for low-control refrigeration and thermometry of thermal qubits, which can
be implemented using electronic spins in diamond. The refrigeration is implemented by a probe, consisting of a
network of interacting spins. The protocol involves two operations: (i) free evolution of the probe; and (ii) a swap
gate between one spin in the probe and the thermal qubitwewish to cool.We showthat if the initial state of the probe
falls within a suitable range, and the free evolution of the probe is both unital and conserves the excitation in the z direction,
then the cooling protocolwill always succeed,with an efficiency that depends on the rate of spin dephasing
and the swap-gate fidelity. Furthermore, measuring the probe after it has cooled many qubits provides an estimate
of their temperature. We provide a specific example where the probe is a Heisenberg spin chain, and suggest a
physical implementation using electronic spins in diamond. Here, the probe is constituted of nitrogen vacancy
(NV) centers, while the thermal qubits are dark spins. By using a novel pulse sequence, a chain of NV centers can
be made to evolve according to a Heisenberg Hamiltonian. This proposal allows for a range of applications, such
as NV-based nuclear magnetic resonance of photosensitive molecules kept in a dark spot on a sample, and it opens
up possibilities for the study of quantum thermodynamics, environment-assisted sensing, andmany-body physics.