Geometric entanglement of a photon and spin qubits in diamond.

Sekiguchi, Yuhei; Yasui, Yuki; Tsurumoto, Kazuya; Koga, Yuta; Reyes, Raustin; Kosaka, Hideo

Geometric nature, which appears in photon polarization, also appears in spin polarization under a zero magnetic field. These two polarized quanta, one travelling in vacuum and the other staying in matter, behave the same as geometric quantum bits or qubits, which are promising for noise resilience compared to the commonly used dynamic qubits. Here we show that geometric photon and spin qubits are entangled upon spontaneous emission with the help of the spin − orbit entanglement inherent in a nitrogen-vacancy center in diamond. The geometric spin qubit is defined in a degenerate subsystem of spin triplet electrons and manipulated with a polarized microwave. An experiment shows an entanglement state fidelity of 86.8%. The demonstrated entangled emission, combined with previously demonstrated entangled absorption, generates purely geometric entanglement between remote matters in a process that is insensitive of time, frequency, and space mode matching, which paves the way for building a noise-resilient quantum repeater network or a quantum internet. Preserving the entanglement of quantum bits is essential for the operation for all quantum technologies. Here, the geometric nature of spins in a diamond nitrogen vacancy is leveraged to improve the fidelity of entanglement with a spontaneously emitted photon.

QUBITS; POLARIZED photons; QUANTUM entanglement; PHOTONS; ELECTRON spin; PHOTON pairs; QUANTUM networks (Optics)

Communications Physics, 2021, Vol 4, Issue 1, p1

2399-3650

Academic Journal

10.1038/s42005-021-00767-1