Quantum Information Processing with Stroboscopic Qubit Interactions

Microwave dressing of superconducting qubits arranges energy level structures that allow bath-engineered cooling, single photon detection, and electromagnetically induced transparency. Application of an additional stroboscopic dispersive tone can induce interactions analogous both to back-action evading measurements in cavity optomechanics and to stimulated Raman transitions in trapped ions. With such stroboscopic interactions, we have recently demonstrated the ability to measure the state of a superconducting transmon qubit via synthetic longitudinal coupling, to adjust dynamically the measurement axes, and to improve such measurements using squeezed vacuum. We now apply the stroboscopic interaction to realize an entangling gate for superconducting qubits, similar to entangling gates routinely employed for trapped ion qubits. This gate generates simultaneous multi-qubit entanglement via a shared photonic mode. The introduction of such periodic interactions in multi-particle systems under constant drive may additionally permit studies of out-of-equilibrium many-body states.