Quantum non-demolition detection of an itinerant single photon using a superconducting qubit
Research Center for Advanced Science and Technology
Nakamura - Usami Group
The University of Tokyo
Superconducting qubits have been successfully applied in many experiments on microwave quantum optics. However, it remains a challenging task to efficiently couple superconducting qubits and photons in a propagating mode, rather than in a cavity mode. Here, we propose a new scheme for generating entanglement between them. Furthermore, we realize quantum non-demolition detection of an itinerant single photon using a superconducting qubit.
In the experiment, we use a superconducting qubit coupled to a 3D microwave cavity in the strong dispersive regime. When a resonant microwave pulse propagating through a waveguide is reflected by the cavity, the photon field interacts with the qubit dispersively through the cavity. If the input state of the microwave pulse contains a single photon, the qubit acquires a phase shift. With a proper tuning of the experimental parameters, the phase shift per photon can be adjusted to π, resulting in a phase-flip of the qubit. After the interaction, we detect the phase-flip of the qubit with a single-shot projective measurement of the qubit and find whether a photon has been reflected or not