A quantum switch for itinerant microwave single photons with superconducting quantum circuits

A classical switch determines which of several inputs to the device passes through the output [1]. In analogy, a quantum switch that coherently links the input to a superposition of several outputs plays an important role in QIP, especially when operating at the fundamental limit where a single photon can be controlled [2]. In this work, we realize such a quantum switch in the microwave regime with superconducting quantum circuits. A microwave cavity, dispersively coupled with a transmon qubit, is used to coherently switch the input single microwave photons emitted from another superconducting circuit. We show that the propagation path of single photons can be coherently manipulated by the qubit and confirm the existence of entanglement between the qubit and the photons’ propagation path. We further demonstrate that the quantum switch can effectively generate heralded entanglement between the qubit and the propagating photonic qubit, thus providing a versatile approach to generate reconfigurable multi-node entanglement in one step. As such, our work provides a prime building block for microwave quantum networks and modular superconducting quantum computing.

[1] M. Pechal, et. al., Physical Review Applied 6, 024009 (2016).

[2] H. J. Kimble, Nature 453, 1023 (2018).