Realization of a Universal Quantum Gate Set for Itinerant Microwave Photons

Abstract

Large-scale quantum computing will likely employ distributed network architectures in which photons, the fundamental quantum units of light, act as mobile carriers of quantum information to communicate between network nodes. Engineering the necessary interactions between two photons is challenging at optical frequencies but is more readily achievable at microwave frequencies. Here, we experimentally demonstrate an entangling two-qubit gate—a fundamental building block of any quantum algorithm—using controlled interactions between itinerant microwave photons.Our setup makes use of the strong coupling between microwave photons and superconducting circuit devices. We use one device to generate single-photon wave packets acting as flying qubits, which are then funneled to a second superconducting circuit engineered to perform one of two operations on the received qubit. The receiving circuit can absorb, act on, and reemit a qubit (a single-qubit gate) or it can shift the phase of a qubit depending on the state of another (a controlled-phase gate). These operations represent a universal set of quantum gates of microwave-photon qubits.We envision this setup being used to generate larger entanglement among many microwave-photon qubits and finding a wide range of applications in superconducting quantum networks.