Device-independent dimension leakage null test on qubits at low operational cost

TL;DR

This paper introduces a low-cost, device-independent null test for qubit dimension leakage, demonstrating its effectiveness on IBM Quantum hardware and revealing deviations beyond known technical imperfections.

Contribution

The paper presents a novel, resource-efficient null test for qubit dimension leakage that is device-independent and experimentally feasible on current quantum hardware.

Findings

Most qubits failed the test by over 10 standard deviations

The test is robust against decoherence and phase shifts

Deviations suggest unknown sources beyond common imperfections

Abstract

We construct a null test of the two-level space of a qubit, which is both device independent and needs a small number of different experiments. We demonstrate its feasibility on IBM Quantum, with most qubits failing the test by more than 10 standard deviations. The robustness of the test against common technical imperfections, like decoherence and phase shifts, and supposedly negligible leakage, indicates that the origin of deviations is beyond known effects.