We report on multiple photon monochromatic quantum oscillations (Rabi oscillations) observed by pulsed EPR (Electron Paramagnetic Resonance) of Mn$^{2+}$ (S=5/2) impurities in MgO. We find that when the microwave magnetic field is similar or large th
an the anisotropy splitting, the Rabi oscillations have a spectrum made of many frequencies not predicted by the S=1/2 Rabi model. We show that these new frequencies come from multiple photon coherent manipulation of the multi-level spin impurity. We develop a model based on the crystal field theory and the rotating frame approximation, describing the observed phenomenon with a very good agreement.
We report on multi-photon Rabi oscillations and controlled tuning of a multi-level system at room temperature (S=5/2 for Mn2+:MgO) in and out of a quasi-harmonic level configuration. The anisotropy is much smaller than the Zeeman splittings, such as
the six level scheme shows only a small deviation from an equidistant diagram. This allows us to tune the spin dynamics by either compensating the cubic anisotropy with a precise static field orientation, or by microwave field intensity. Using the rotating frame approximation, the experiments are very well explained by both an analytical model and a generalized numerical model. The calculated multi-photon Rabi frequencies are in excellent agreement with the experimental data.
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 functin of pho
ton number $n_{rm max}$ and spin system size $N$. A sharp transition in the distribution of the Rabi frequency is found at $n_{rm max}approx N$. The width of the Rabi frequency spectrum diverges as $sqrt{N}$ at this point. For increased number of photons $n_{rm max}>N$, the Rabi frequencies converge to a value proportional to $sqrt{n_{rm max}}$. 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 towards quantum computing implementation with magnetic spins, using cavity quantum-electrodynamics techniques.
On-chip Electron Spin Resonance (ESR) of magnetic molecules requires the ability to precisely position nanosized samples in antinodes of the electro-magnetic field for maximal magnetic interaction. A method is developed to entrap micro-crystals conta
ining spins in a well defined location on a substrates surface. Traditional cavity ESR measurements are then performed on a mesoscopic crystal at 34 GHz. Polycrystalline diluted Cr$^{5+}$ spins were entrapped as well and measured while approaching the lower limit of the ESR sensitivity. This method suggests the feasibility of on-chip ESR measurements at dilution refrigerator temperatures by enabling the positioning of samples atop an on-chip superconducting cavity.
