Controllable interaction between photons and distant spins via vacuum Rabi oscillations

This study investigates the coherent interaction between distant semiconductor spin qubits and microwave photons. Specifically, the authors aim to demonstrate time-domain vacuum Rabi oscillations between single electron spins and a superconducting resonator, and to use these oscillations to transfer quantum information between two spatially separated qubits on the same chip.

The researchers engineered a hybrid device featuring two double quantum dots (DQDs) located at opposite ends of a superconducting NbTiN resonator. Each DQD hosts a single electron spin qubit. By applying magnetic field gradients via integrated micromagnets, the team achieved strong spin-photon coupling. The experiment involved pulsing the system between uncoupled, resonant, and dispersive regimes to initialize the spins, drive vacuum Rabi oscillations, and perform state transfer. The team also verified the Fock-state nature of the photons by observing the acceleration of Rabi oscillations, which scales with the square root of the photon number.

The study successfully observed multiple vacuum Rabi oscillations between each spin qubit and the cavity. By concatenating these oscillations, the authors demonstrated the transfer of a single excitation from one spin to the other via the cavity. Furthermore, they confirmed that the cavity is prepared in a Fock state after a single photon emission, evidenced by the accelerated Rabi frequency when the second qubit interacts with the populated resonator. These results validate the use of superconducting cavities as a bus for interconnecting semiconductor spin qubits.

This work provides a critical building block for scalable quantum computing architectures. By demonstrating that spin qubits can interact coherently with microwave photons over macroscopic distances (250 micrometers), the study establishes a pathway for linking distant quantum processing modules. This capability is essential for building distributed quantum networks and interfacing spin-based processors with photonic links.