Approaching optimal entangling collective measurements on quantum computing platforms

TL;DR

This paper demonstrates experimentally optimal collective measurements on various quantum platforms to enhance multi-parameter quantum metrology, maintaining quantum advantage even under decoherence.

Contribution

It introduces and implements theoretically optimal single- and two-copy collective measurements for estimating non-commuting qubit rotations across multiple quantum systems.

Findings

Quantum-enhanced sensing with persistent metrological gain.

Implementation of optimal measurements on superconducting, trapped-ion, and photonic systems.

Insights into the uncertainty principle through collective measurement analysis.

Abstract

Entanglement is a fundamental feature of quantum mechanics and holds great promise for enhancing metrology and communications. Much of the focus of quantum metrology so far has been on generating highly entangled quantum states that offer better sensitivity, per resource, than what can be achieved classically. However, to reach the ultimate limits in multi-parameter quantum metrology and quantum information processing tasks, collective measurements, which generate entanglement between multiple copies of the quantum state, are necessary. Here, we experimentally demonstrate theoretically optimal single- and two-copy collective measurements for simultaneously estimating two non-commuting qubit rotations. This allows us to implement quantum-enhanced sensing, for which the metrological gain persists for high levels of decoherence, and to draw fundamental insights about the interpretation of the uncertainty principle. We implement our optimal measurements on superconducting, trapped-ion and photonic systems, providing an indication of how future quantum-enhanced sensing networks may look.