Weak-to-strong transition of quantum measurement in a trapped-ion system

Yiming Pan, Jie Zhang, Eliahu Cohen, Chun wang Wu, Ping Xing Chen, Nir Davidson

Research output: Contribution to journalArticlepeer-review

46 Scopus citations


Quantum measurement remains a puzzle through its stormy history from the birth of quantum mechanics to state-of-the-art quantum technologies. Two complementary measurement schemes have been widely investigated in a variety of quantum systems: von Neumann’s projective ‘strong’ measurement and Aharonov’s weak measurement. Here, we report the observation of a weak-to-strong measurement transition in a single trapped 40Ca+ ion system. The transition is realized by tuning the interaction strength between the ion’s internal electronic state and its vibrational motion, which play the roles of the measured system and the measuring pointer, respectively. By pre- and post-selecting the internal state, a pointer state composed of two of the ion’s motional wavepackets is obtained, and its central-position shift, which corresponds to the measurement outcome, demonstrates the transition from the weak-value asymptotes to the expectation-value asymptotes. Quantitatively, the weak-to-strong measurement transition is characterized by a universal transition factor e−Γ2/2, where Γ is a dimensionless parameter related to the system–apparatus coupling. This transition, which continuously connects weak measurements and strong measurements, may open new experimental possibilities to test quantum foundations and prompt us to re-examine and improve the measurement schemes of related quantum technologies.

Original languageEnglish
Pages (from-to)1206-1210
Number of pages5
JournalNature Physics
Issue number12
StatePublished - Dec 2020

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© 2020, The Author(s), under exclusive licence to Springer Nature Limited.


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