All-optical quantum thermometry based on spin-level cross-relaxation and multicenter entanglement under ambient conditions in SiC

All-optical thermometry technique based on the energy level cross-relaxation in atomic-scale spin centers in SiC is demonstrated. This technique exploits a giant thermal shift of the zero-field splitting for centers in the triplet ground state, S=1, undetected by photoluminescence (so called dark centers) coupling to neighbouring spin-3/2 centers which can be optically polarized and read out (bright centers), and does not require radiofrequency fields. EPR was used to identify defects. The width of the cross-relaxation line is almost an order of magnitude smaller than the width of the excited state level-anticrossing line, which was used in all-optical thermometry and which can not be significantly reduced since determined by the lifetime of the excited state. With approximately the same temperature shift and the same signal intensities as for excited state level-anticrossing, cross-relaxation signal makes it possible to increase the sensitivity of the temperature measurement by more than an order of magnitude. Temperature sensitivity is estimated to be approximately 10 mK/Hz(1/2) within a volume about 1 mu(3), allocated by focused laser excitation in a scanning confocal microscope. Using cross-relaxation in the ground states of bright spin-3/2 centers and dark S=1 centers for temperature sensing and ground state level anti-crossing of bright spin-3/2 centers an integrated magnetic field and temperature sensor with submicron space resolution can be implemented using the same spin system. The coupling of individually addressable bright spin-3/2 centers connected by a chain of dark S=1 spins, could be considered in quantum information processing and multicenter entanglement under ambient conditions. (C) 2018 Author(s).