In a Spanish-French collaboration, Tomás Ramos and Juan José García-Ripoll from the CSIC Institute of Fundamental Physics together with the group of Olivier Buisson and Nicolas Roch at the Institute Néel, have proposed and experimentally demonstrated a new read-out scheme for superconducting qubits. The new scheme provides provides reliable quantum non-demolition (QND) measurements using a strong “cross-Kerr” coupling to polariton read-out modes, while minimizing other sources of noise. In a first experimental demonstration of this new technique, it has been possible to measure a 99% preservation of probabilities or “QND-ness”, a readout fidelity of 97.4%, and a short measurement time of 50 ns.
The refinement of our new readout scheme may allow measurements with a high signal-to-noise ratio even without amplification of the signals. This may reduce the overhead and complexity of superconducting quantum chips and thus facilitate the scaling up of these quantum technologies to large sizes, as well as the implementation of quantum error correction and fault-tolerant quantum computation in the future.
The results of this research have been recently published in Physical Review X (open access), which can be found in the link: Fast High-Fidelity Quantum Nondemolition Qubit Readout via a Nonperturbative Cross-Kerr Coupling