The case against entanglement improved measurement precision

TL;DR

This paper challenges the widely held belief that quantum entanglement enhances measurement precision, arguing that theoretical proofs are based on misinterpretations and that experimental claims of surpassing classical limits are often misleading or incorrect.

Contribution

It critically analyzes and refutes the claims of entanglement-enhanced metrology, providing a new perspective that aligns better with empirical evidence and suggesting modifications to quantum measurement theory.

Findings

Theoretical proofs of entanglement-based precision enhancement are flawed.

Experimental claims of surpassing classical limits are often misleading or incorrect.

Introducing a simple physical principle improves agreement between theory and experiment.

Abstract

It is widely accepted that quantum entanglement between otherwise independent sensors can yield a measurement precision beyond that achievable when the same resources are employed without entanglement \cite{Helstrom1969, Holevo1973a, Caves1980a, Caves1981, Wootters1981, Yurke1986, Wu1986, Xiao1987, Slusher1987, Shapiro1989, Wineland1992, Polzik1992, Kitagawa1993, Braunstein1994, Wineland1994, Sanders1995, Bollinger1996, Ou1997, Dowling1998,Soerensen1998, Brif1999, Childs2000, Fleischhauer2000, Meyer2001, Geremia2003, Giovannetti2004, Kok2004, Leibfried2004, Leibfried2005, Giovannetti2006, Nagata2007, Appel2009, Gross2010, Leroux2010, Zwierz2010,DemkowiczDobrzanski2012, Zwierz2012,Aasi2013,Pezze2018,Tse2019,Casacio2021}. Here we show that theoretical proofs of entanglement enhanced metrology are based on a misinterpretation of \emph{can't} theorems as \emph{can} theorems. In concert, we dissect claims of an experimental precision beyond the classical limits and detail where comparisons are misleading, incomplete or incorrect to show that the precision of optimised measurements which forgo entanglement has not been surpassed. In doing so, we highlight a significant discrepancy between experimentally reported uncertainties and the current predictions of quantum measurement theory. The discrepancy can be resolved by introducing a simple physical principle which demonstrates better agreement to empirical evidence. We thus provide viable avenues as to where standard interpretations of quantum mechanics should be modified in order to better predict measurement outcomes.