A Dressed Spin Qubit in Silicon*

Coherent dressing of a quantum two-level system has been demonstrated on a variety of systems, including atoms, self-assembled quantum dots, and superconducting quantum bits, and can be demonstrated by measuring Rabi oscillations, or a Mollow triplet in the spectrum. It can be used to gain access to a new quantum system with improved properties - a different and tunable level splitting, faster and easier control, and longer coherence times. In our work we investigate the properties of the dressed, donor-bound electron spin in silicon, and probe its potential for the use as quantum bit in scalable architectures. Here, the two dressed spin-polariton levels constitute the quantum bit. The dressed qubit can be coherently driven with an oscillating magnetic field, an oscillating electric field, by frequency modulating the driving field, or by a simple detuning pulse. We measure coherence times of T2* $=$ 2.4 ms and T2 $=$ 9 ms (Hahn echo), one order of magnitude longer than those of the undressed qubit.