Quantum-dot spin-photon entanglement via frequency downconversion to telecom wavelength

TLDR: The present technique advances the III–V semiconductor quantum-dot spin system as a promising platform for long-distance quantum communication by frequency downconversion of a spontaneously emitted photon from a singly charged quantum dot to a wavelength of 1,560 nanometres.

Abstract: Future quantum networks will combine ideally stationary quantum bits (qubits), such as single electron spins, with 'flying' qubits, which are photons that transfer quantum states between distant qubits. It has therefore been a long-standing challenge in the field of quantum computation and communication to couple a single electron spin to a single photon in a solid-state platform. Two groups working independently have now achieved that goal, by demonstrating entanglement between a photon and a single electron spin trapped in a semiconductor 'quantum dot' structure. The quantum dot acts as the stationary node. This achievement is a small step towards eventual implementation of quantum networks that can support long-distance quantum communication.