Manipulations of a transmon qubit with a null-biased electro-optic fiber link.

In recent years, significant progress has been made in the field of superconducting quantum circuits, particularly in improving the complexity of quantum processors for large-scale quantum computing and quantum simulation tasks. To enable the execution of quantum information processing tasks on large-scale quantum circuits containing millions of qubits, it is essential to minimize thermal effects on control and measurement lines, ensuring that circuit components are superconducting and that qubits are not significantly thermally excited. Recent studies have shown that a quadrature-biased electro-optic fiber link can operate qubits with a much reduced thermal load, thereby facilitating the simultaneous operation of a large number of qubits. Expanding on this, here we propose and demonstrate that coherent manipulations of superconducting qubits can also be achieved by setting the bias point of the electro-optic modulator at the null point instead of the quadrature point. Major advantages of our null-point bias method include further reduction of the thermal load and improvement of the signal-to-noise ratio, and relaxed requirement for experimental implementations. Simultaneous control of two qubits is also demonstrated using the proposed null-biased fiber-optic link, which is the first time to the best of our knowledge.