Informationally Complete Distributed Metrology Without a Shared Reference Frame

TL;DR

This paper introduces a reversed-encoding method in quantum metrology that overcomes fundamental restrictions caused by lack of shared reference frames, enabling complete quantum information recovery in distributed quantum sensing.

Contribution

The authors propose a novel reversed-encoding technique that bypasses the no-go theorem and allows for RF-independent distributed quantum metrology with optimal measurement strategies.

Findings

Reversed-encoding enables recovery of quantum Fisher information without shared RF.

Local Bell-state measurements are optimal for saturating the quantum Fisher information.

Method mitigates decoherence-like noise caused by RF misalignment.

Abstract

In quantum information processing, implementing arbitrary preparations and measurements on qubits necessitates precise information to identify a specific reference frame (RF). In space quantum communication and sensing, where a shared RF is absent, the interplay between locality and symmetry imposes fundamental restrictions on physical systems. A restriction on realizable unitary operations results in a no-go theorem prohibiting the extraction of locally encoded information in RF-independent distributed metrology. Here, we propose a reversed-encoding method applied to two copies of local-unitary-invariant network states. This approach circumvents the no-go theorem while simultaneously mitigating decoherence-like noise caused by RF misalignment, thereby enabling the complete recovery of the quantum Fisher information (QFI). Furthermore, we confirm local Bell-state measurements as an optimal strategy to saturate the QFI. Our findings pave the way for the field application of distributed quantum sensing, which is inherently subject to unknown RF misalignment and was previously precluded by the no-go theorem.