Microwave photonic quantum processor

A quantum computing circuit for performing state operations on qubits, the quantum computing circuit comprising:

• a dual-rail structure comprising a set of dual-rail transmission-line elements, each dual-rail transmission-line element comprising a first transmission line and a second transmission line for allowing microwave photons to propagate through the first and/or second transmission lines, a respective propagating microwave photon having a specific quantum state, and encoding a qubit, the quantum state depending at least on which one of the first and second transmission lines the respective microwave photon propagates;
• a set of single-qubit gates, each single-qubit gate comprising a) a first phase shifter, a second phase shifter, and a first directional coupler, or b) a first directional coupler, a second directional coupler, and a first phase shifter, the respective phase shifter being configured to introduce a phase shift to a carrier wave of the microwave photon propagating through the respective phase shifter, the respective directional coupler being configured to transfer or partially transfer a respective microwave photon propagating through the respective single-qubit gate from the first transmission line to the second transmission line, or vice versa;
• and
• a set of two-qubit gates, each two-qubit gate comprising an oscillator system, the oscillator system comprising an artificial atom, an oscillator coupled to the artificial atom, two inputs and two corresponding outputs, each inputs and its corresponding output being coupled to the same transmission line of a respective dual-rail transmission-line element, two-qubit gate forms a Rabi oscillator configured to induce an additional phase-shift when two microwave photons are simultaneously received at the oscillator system, one at each of its two inputs, compared to a phase-shift induced when only a single microwave photon is received at the oscillator system.