N@C-60 and P@C-60 as quantum bits

Due to their long electron spin relaxation times, the endohedral fullerenes N@C-60 and P@C-60 are good candidates for the implementation of qubits in an electron spin quantum computer. A central operation in this context is the rotation of the spin direction by an arbitrary angle. In the present experiment, this nutation behavior was studied in pulsed electron spin resonance measurements. We show that, even at room temperature, about 50 Rabi oscillations (about 100 qubit operations) can be performed without refocusing the spin system, although inhomogeneities are present. A special feature of the group V endohedral fullerenes is the electron spin S = 3/2, which complicates the nutation behavior. The zero-field splitting at low temperature gives rise to different nutation frequencies for the (1/2,-1/2) transition and the (+/-3/2, +/-1/2) transitions. The frequency ratio is 2/3(1/2).