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

TL;DR

This paper explores the dynamics of a strongly-driven, microwave-dressed electron spin qubit in silicon, demonstrating the breakdown of the rotating wave approximation through experimental and numerical analysis.

Contribution

It introduces a method to study the regime where the rotating wave approximation fails using frequency modulation, avoiding high microwave powers incompatible with cryogenic environments.

Findings

Deviations from normal Rabi oscillations observed

Numerical simulations match experimental data well

Demonstrates a new regime for driven spin qubits

Abstract

We investigate the dynamics of a strongly-driven, microwave-dressed, donor-bound electron spin qubit in silicon. A resonant oscillating magnetic field $B_1$ is used to dress the electron spin and create a new quantum system with a level splitting proportional to $B_1$. The dressed two-level system can then be driven by modulating the detuning $\Delta\nu$ between the microwave source frequency $\nu_{\rm MW}$ and the electron spin transition frequency $\nu_e$ at the frequency of the level splitting. The resulting dressed qubit Rabi frequency $\Omega_{R\rho}$ is defined by the modulation amplitude, which can be made comparable to the level splitting 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.