The Shaping of Flying Qubits based on Quantum Optimal Control Theory

The control of flying qubits carried by itinerant photons is ubiquitous in quantum communication networks. In addition to their logical states, the shape of flying qubits must also be tailored to match the remote receiver. In this paper, we introduce the quantum optimal control theory to the design of flying-qubit shaping protocols. A gradient-based algorithm is proposed for the generation of arbitrary-shape flying qubits with general non-ideal emitters. Simulations show that, as a joint control with the traditionally used tunable coupler, coherent driving fields can be applied to the shaping when the coupling strength is fixed or limited. The optimized control protocols can effectively suppress unwanted level leakage and multi-photon radiation. The method provides a systematic approach to high-fidelity control of flying qubits using realistic quantum devices.