Magnetic strong coupling in a spin-photon system and transition to classical regime
I. Chiorescu, Nickolas Groll, Sylvain Bertaina, Takashi Mori, Seiji Miyashita · Physical Review B · 2010
We study the energy level structure of the Tavis-Cumming model applied to an ensemble of independent magnetic spins $s=1/2$ coupled to a variable number of photons. Rabi splittings are calculated and their distribution is analyzed as a function of photon number ${n}_{\text{max}}$ and spin system size $N$. A sharp transition in the distribution of the Rabi frequency is found at ${n}_{\text{max}}\ensuremath{\approx}N$. The width of the Rabi frequency spectrum diverges as $\sqrt{N}$ at this point. For increased number of photons ${n}_{\text{max}}>N$, the Rabi frequencies converge to a value proportional to $\sqrt{{n}_{\text{max}}}$. This behavior is interpreted as analogous to the classical spin-resonance mechanism where the photon is treated as a classical field and one resonance peak is expected. We also present experimental data demonstrating cooperative, magnetic strong coupling between a spin system and photons, measured at room temperature. This points toward quantum computing implementation with magnetic spins, using cavity quantum-electrodynamics techniques.