Tunable phase shifters for microwaves

We investigate tunable phase shifters for propagating microwave photons consisting of lumped elements coupled to a transmission line. We show that these types of phase shifters can exhibit full transmission over wide range of frequencies while maintaining high tunability. In this framework, we demonstrate a magnetic-flux-tunable phase shifter based on three equidistant superconducting quantum interference devices (SQUIDs) on a transmission line. We experimentally implement the phase shifter and demonstrate that it produces a broad range of phase shifts and full transmission within the experimental uncertainty. Together with previously demonstrated beam splitters, this phase shifter can be utilized to implement arbitrary single-qubit gates for qubits based on propagating microwave photons. These results complement previous demonstrations of on-demand single-photon sources and detectors, and hence assist in the pursuit of an all-microwave quantum computer based on propagating photons.