Passive leakage removal unit based on a disordered transmon array
Phys. Rev. A 112, 032408 – Published 3 September, 2025
DOI: https://doi.org/10.1103/bxqs-y662
Abstract
Leakage out from the qubit subspace compromises standard quantum error correction protocols and poses a challenge for practical quantum computing. We propose here a passive leakage removal unit based on an array of coupled disordered transmons and last-site reset by feedback-measurement or dissipation. We find that the unit effectively removes leakage with minimal effect on the qubit subspace by taking advantage of energy level disorder for the qubit subspace and resonant leakage energy levels. There are two optimal measurement rates for removing leakage, which we show analytically to correspond to the characteristic timescales of the propagation and disintegration of the leakage excitation. The performance of the leakage removal unit depends on the strength of disorder, coupling between the transmons, and the length of the array. We simulate the system under experimentally feasible parameters and present an optimal configuration. Our approach is readily compatible with existing superconducting quantum processors, considering realistic conditions.
