Strong coupling of a single electron in silicon to a microwave photon

We demonstrate a hybrid circuit quantum electrodynamics (cQED) architecture in which a single electron in a Si/SiGe double quantum dot is dipole-coupled to the electric field of microwave photons in a superconducting cavity. Vacuum Rabi splitting is observed in the cavity transmission when the transition energy of the single-electron charge qubit matches that of a cavity photon, demonstrating that our device is in the strong coupling regime. The achievement of strong coupling is largely facilitated by an exceptionally low charge decoherence rate of 5 MHz and paves the way toward a wide range of cQED experiments with quantum dots, such as non-local qubit interactions \footnote{J. Majer \textit{et al.}, \textit{Nature} \textbf{449}, 443 (2007).}, strong spin-cavity coupling \footnote{J. J. Viennot \textit{et al.}, \textit{Science} \textbf{349}, 408 (2015).} and single photon generation \footnote{A. A. Houck \textit{et al.}, \textit{Nature} \textbf{449}, 328 (2007).}.