Breaking the rotating wave approximation for a strongly-driven, dressed, single electron spin

Arne Laucht, Stephanie Simmons, Rachpon Kalra, Guilherme Tosi, Juan P. Dehollain, Juha T. Muhonen, Solomon Freer, Fay E. Hudson, Kohei M. Itoh, David N. Jamieson, Jeffrey C. McCallum, Andrew S. Dzurak, Andrea Morello

Published 2016-06-08Version 1

We investigate the dynamics of a strongly-driven, microwave-dressed, donor-bound electron spin qubit in silicon. A resonant oscillating magnetic field $B_1$ dresses the electron spin and creates a new quantum system with a level splitting defined by the spin Rabi frequency $\Omega_R$. The dressed two-level system can then be driven by modulating the detuning $\Delta$ between the microwave source frequency $\omega_{\rm MW}$ and the electron spin transition frequency $\omega_e$ at frequency $\Omega_R$. Here, the dressed qubit Rabi frequency $\Omega_{R\rho}$ is defined by the modulation amplitude, which can be made comparable to $\Omega_R$ using frequency modulation on the microwave source. This allows us to investigate the regime where the rotating wave approximation breaks down, without requiring microwave power levels that would be incompatible with a cryogenic environment. We observe clear deviations from normal Rabi oscillations and can numerically simulate the time evolution of the states in excellent agreement with the experimental data.