Can Quantum Computers Do Nothing?
Quantum computing platforms are subject to contradictory engineering
requirements: qubits must be protected from mutual interactions when idling
('doing nothing'), and strongly interacting when in operation. If idling qubits
are not sufficiently protected, information can 'leak' into neighbouring
qubits, become non-locally distributed, and ultimately inaccessible. Candidate
solutions to this dilemma include patterning-enhanced many-body localization,
dynamical decoupling, and active error correction. However, no
information-theoretic protocol exists to actually quantify this information
loss due to internal dynamics in a similar way to e.g. SPAM errors or dephasing
times. In this work, we develop a scalable, flexible, device non-specific
protocol for quantifying this bitwise idle information loss based on the
exploitation of tools from quantum information theory. We implement this
protocol in over 3500 experiments carried out across 4 months (Dec 2023 - Mar
2024) on IBM's entire Falcon 5.11 series of processors. After accounting for
other sources of error, and extrapolating results via a scaling analysis in
shot count to zero shot noise, we detect idle information leakage to a high
degree of statistical significance. This work thus provides a firm quantitative
foundation from which the protection-operation dilemma can be investigated and
ultimately resolved.
Alexander Nico-Katz Nathan Keenan John Goold