Cavity Quantum Electrodynamics Effects with Nitrogen Vacancy Center Spins in Diamond and Microwave Resonators at Room Temperature

Abstract

Cavity quantum electrodynamics (C-QED) effects, such as Rabi splitting, Rabi oscillations and superradiance, have been demonstrated with nitrogen vacancy center spins in diamond in microwave resonators at cryogenic temperature. In this article we explore the possibility to realize strong collective coupling and the resulting C-QED effects with ensembles of spins at room temperature. Thermal excitation of the individual spins by the hot environment leads to population of collective Dicke states with low symmetry and a reduced collective spin-microwave field coupling. However, we show with simulations that the thermal excitation can be compensated by spin-cooling via optical pumping. The resulting population of Dicke states with higher symmetry implies strong coupling with currently available high-quality resonators and enables C-QED effects with potential applications in quantum sensing and quantum information processing.

Cavity Quantum Electrodynamics Effects of Optically Cooled Nitrogen-Vacancy Centers Coupled to a High Frequency Microwave Resonator

“…To proceed, we firstly translate the spin population polarization into the average of the Dicke states numbers J, M to illustrate more intuitively the collective coupling strength. In our previous study [14], we show that these averaged numbers can be calculated as M = J 0 (2p − 1), J(J + 1) = (2p − 1) 2 J 0 (J 0 + 1) + 6p(p − 1)J 0 with shows the dynamics of the normalized intra-resonator photon number for the laser power 0.01, 0.3, 1, 10 W (black solid, blue dashed, red dash-dotted and green solid line), where the curves are vertically shifted for the sake of clarity. Panel (c) shows the steady-state intra-resonator photon number as function of the detuning of the microwave driving field frequency ω d and the microwave resonator frequency ωc for the laser power 0.01, 0.3, 1, 10 W(black solid, blue dashed, red dash-dotted and green solid line).…”

“…In this section, we demonstrate that it can be also utilized to realize the collective strong coupling with the cooled microwave mode, and to manifest the cavity-QED effects at room temperature. These effects have been studied previously by us [14] with a model, which treats the NV spins as two-level systems and the optical spin cooling effectively with single spin relaxation rate. Here, with the more advanced model, we are able to estimate the laser power required to observe these C-QED effects, which can guide directly the experimental research in future.…”

“…A sufficiently cooled microwave mode may ap-proach pure quantum states and permit study of quantum entanglement [10], quantum gate operations [13] and quantum thermodynamics [11], and it can also improve the measurement sensitivity in electron and nuclear spin resonance experiments [3,12]. Encouraged by the unambiguous demonstration of cavity quantum electrodynamics (C-QED) effects with the triplet spins of pentacene molecules at room temperature [21], we showed in a recent publication [14], that the optically cooled NV spins permit the realization of C-QED effects at room temperature, such as Rabi oscillations, Rabi splittings and stimulated superradiance.…”

“…To describe more precisely the optical spin cooling and the NV spin-resonator collective coupling, we extend the standard Jaynes-Cumming (JC) model for many twolevel systems as used in Ref. [14] to account for all the electronic and spin levels of NV centers in Sec. II, see Fig.…”