Transducer leakage error suppression using invariant-based shortcut

Research Question and Approach

This paper addresses the challenge of leakage errors in hybrid quantum systems, which consist of a semiconductor spin qubit and a superconducting transmon qubit coupled via a superconducting resonator. In these systems, unwanted transitions to non-computational energy levels—often caused by the multi-level nature of the transmon and the complex charge configurations of the spin qubit—degrade gate fidelity. The authors employ the theory of Lewis-Riesenfeld (LR) dynamical invariants to design optimized control pulses. By treating leakage as a perturbation, they derive a control scheme that minimizes the sensitivity of the system to out-of-subspace transitions, effectively confining the quantum dynamics within the desired computational subspace.

The study demonstrates that the invariant-based shortcut protocol significantly outperforms traditional control methods, such as the standard pi-pulse, derivative removal by adiabatic gate (DRAG), and counter-diabatic driving. Numerical simulations show that the optimized pulses can suppress the leakage probability to a minimum of 0.01. Furthermore, the protocol maintains a gate fidelity exceeding 99% even in the presence of decoherence and control errors. The authors show that their method provides a robust framework for high-fidelity iSWAP gate operations and entanglement generation, offering a scalable path for manipulating hybrid quantum systems.

Hybrid quantum systems are promising for quantum computing because they combine the long coherence times of spin qubits with the fast, high-fidelity gate operations of superconducting qubits. However, the complex energy landscapes of these systems make them prone to leakage errors that can destroy quantum information. This research provides a systematic, analytical framework to mitigate these errors, which is essential for the practical implementation of robust, high-performance quantum information processing in solid-state architectures.