Innsbruck physicists propose using logical qubits to detect faint, rare signals

[GhostRider89]

Quantum error correction is usually thought of as a tool for computing, but it may help with sensing too. Quantum Zeitgeist reports on a paper led by Robert Ott of the University of Innsbruck, with colleagues including Torsten Zache, Soonwon Choi, Adam Kaufman and Hannes Pichler, proposing a way to use logical qubits to detect rare, randomly timed signals

The problem is picking out weak pulses that arrive at random times against a background of constant noise. When the noise rate is much higher than the signal rate, standard sensing with ordinary qubits becomes very inefficient, because noise drowns out the rare events

The proposed method deliberately weakens each signal so it imprints only a tiny phase on the logical qubit. Error correction measurements then look for higher order correlations that separate real signals from noise. The approach was shown with calculations and simulations using the seven qubit Steane code, and the authors say it could work with other codes

Comparing three strategies, the team found the logical approach beats standard sensing when noise far exceeds the signal rate. Simple error detection does worse, because it throws away real signals along with the noise. The benefit comes from error correction extending coherence enough to outweigh the weakened signal

This is a theoretical result, so no hardware has tried it yet, and the authors are clear that error correction does not help sensing in every situation. Still, finding a new job for logical qubits is valuable. Fields from materials science to fundamental physics rely on detecting faint signals

Could error correction become a standard tool for quantum sensors? And which experiments would benefit most from detecting rare events?

Logical Qubits Boost Sensitivity To Faint, Random Signalsquantumzeitgeist.com