# Physicists Model Andreev Qubit Readout Without Ancillae at up to 99.85% Accuracy

- Published: 2026-11-07 00:41 UTC
- Section: Digital & Computing › Quantum technology
- Tags: Andreev qubit readout, quantum dot Josephson junction, nondestructive measurement, quantum error correction, Josephson effect, superconducting circuit
- URL: https://realtech.media/news/rt-c6af410e7456db45d4adddb8_physicists_model_andreev/

**Researchers calculated that dynamic interference supercurrents allow nondestructive readout of Andreev quantum dots without auxiliary qubits.**

![Physicists Model Andreev Qubit Readout Without Ancillae at up to 99.85% Accuracy](https://realtech.media/media/2026/11/65570be0d1b904c6.jpg)
*Lab mol (Ilia Litvinov), Wikimedia Commons, CC BY 4.0*

Physicists from the Beijing Institute of Technology and the University of São Paulo reported a method to read Andreev quantum dot qubits without auxiliary ancilla qubits in Physical review. B. [1]. The theoretical protocol uses the macroscopic oscillatory supercurrent produced by the quantum dot Josephson junction itself to measure arbitrary superposition states. According to the team's numerical simulations, the readout achieves accuracies of 99.52%, 99.81%, and 99.85%, depending on the number of measurement cycles [1].

Existing quantum nondemolition protocols typically transfer quantum information to helper ancilla systems, which requires extra steps and repeated reinitializations. In the proposed setup, an indium arsenide nanowire forms a quantum dot coupled to superconductors in a closed circuit. The interference between the many-body eigenstates of the Andreev qubit creates an alternating-current-like supercurrent without an applied external voltage [1].

## Intrinsic Current Oscillations

The authors demonstrated that information about the qubit is directly encoded into the time-dependent behavior of this macroscopic current [1]. The constant component of the supercurrent and the oscillation amplitude define the relative probabilities of states 0 and 1 in the superposition. Meanwhile, the initial phase of the time-dependent oscillation reveals the relative quantum phase between the two eigenstates [1].

## Magnetic Detection via SQUID

To perform measurements with minimal backaction, the proposal employs an external superconducting quantum interference device placed near the circuit. The sensor monitors the weak magnetic field generated by the oscillating supercurrent through inductive coupling [1]. Because this coupling remains faint, the backaction on the quantum dot remains low enough to approach the nondestructive measurement limit under standard noise conditions [1].

The authors noted that the protocol relies on established components and realistic experimental parameters, requiring no auxiliary qubits or repetitive system reinitializations [1].

## Sources

1. [Physical review. B./Physical review. B](https://doi.org/10.1103/6gkt-hghj)
2. [SciTechDaily](https://scitechdaily.com/scientists-find-a-clever-way-to-read-quantum-information-without-destroying-it)

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Source: RealTech, realtech.media — https://realtech.media/news/rt-c6af410e7456db45d4adddb8_physicists_model_andreev/