Control on the Sensor Coherence of Transmon Superconducting Qubit via the Gradient Descent Algorithm

Abstract

Quantum systems based on superconducting circuits with qubits with quantized energy levels serve as an efficient physical background for constructing different quantum devices, for instance, quantum sensors. The important class of such engineering devices belongs to the systems with quantum tunneling effects, like Josephson junctions, where the set of energy levels is influenced by the external fields. These fields change the phase properties of the measuring qubits, and, in this way, they can be detected. The weakly anharmonic oscillator is often referred as a transmon qubit. Such qubits are constructed with superconducting capacitor structures connected by Josephson junctions, they can be controlled by microwave pulses of a few nanoseconds. The quantum sensing mechanism studied here is based on coupling the measuring transmon superconducting qubits with magnetic materials. The sensing protocol of Ramsey Fringes interferometry covers several stages and demands high-quality control over the sensor coherence. Although the weakly nonlinear properties of transmons prevent the sensing procedure from the strong influence of external perturbations, nevertheless, the extension of the coherence time interval and minimization of the dephasing effects are still a matter of great importance. Here we discuss the improvement of the quantum sensor performance by the application of feedback control in the form of gradient descent algorithm over the dephasing factor-function.