Isophoric News · Tuesday, October 27, 2026
Physicists propose reading an Andreev qubit through the supercurrent it produces, in a theoretical study
A study in Physical Review B proposes a way to read the state of an Andreev qubit, a type of quantum bit built from a quantum dot between two superconductors, without the extra "ancilla" qubits that other non-destructive readout methods need, according to a release from FAPESP, Brazil's São Paulo research foundation, carried by Phys.org. The authors, led by José Carlos Egues of the University of São Paulo and Yugui Yao of the Beijing Institute of Technology, calculate that the qubit's own oscillating supercurrent carries its state and that a nearby SQUID, a sensitive magnetic-field detector, could read it with little disturbance. The paper's abstract says the readout could come "arbitrarily close to the nondestructive limit" under currently available experimental capabilities. The study is entirely theoretical. The authors ran simulations with noise and the detector's back-action and report accuracies of 99.52%, 99.81% and 99.85%, depending on the number of measurements, according to the release. Egues said the method "doesn't eliminate the fundamental problem of quantum measurement," and that the numbers used are realistic but the proposed device geometry does not yet exist. If experiments confirm the prediction, the release says, it could give a simpler way to read such qubits.
