Quantum leakage detection using a model-independent dimension witness

Understand

Users of quantum computers must be able to confirm they are indeed functioning as intended, even when the devices are remotely accessed.

• In particular, if the Hilbert space dimension of the components are not as advertised -- for instance if the qubits suffer leakage -- errors can ensue and protocols may be rendered insecure.
• We refine the method of delayed vectors, adapted from classical chaos theory to quantum systems, and apply it remotely on the IBMQ platform -- a quantum computer composed of transmon qubits.
• The method witnesses, in a model-independent fashion, dynamical signatures of higher-dimensional processes.