BRIEF RESEARCH REPORT article
Front. Quantum Sci. Technol.
Sec. Quantum Information Theory
Volume 4 - 2025 | doi: 10.3389/frqst.2025.1601795
This article is part of the Research TopicOpen Quantum Systems in Quantum TechnologiesView all 4 articles
Joint observables induced by indirect measurements in cavity QED
Provisionally accepted
Kalle Raikisto
Kimmo Luoma*- University of Turku, Turku, Finland
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A fundamental feature of quantum mechanics is that there are observable pairs that cannot be measured jointly, such as observables corresponding to position and momentum or spin direction measurements. However, unsharp versions of non-jointly measurable observables may become jointly measurable. In this work, we investigate the joint measurability of time-continuous observ-ables emerging from indirect time-continuous measurements. In particular, we study a paradigmatic situation where a qubit is interacting with a mode of light in a cavity and the light escaping the cavity is continuously monitored. We find that the properties of the observables can be tuned by changing the type of the monitoring scheme or by tuning the initial state of the cavity. In particular, we demonstrate that heterodyne measurements are a joint measurement of a noisy homodyne measurement of a pair of canonical quadratures. Moreover, we investigate the purity of the induced qubit observables as a function of the noise.
Keywords: quantum mechanics, Quantum information, Foundations of quantum measurement, open quantum systems, quantum communication
Received: 28 Mar 2025; Accepted: 29 Aug 2025.
Copyright: © 2025 Raikisto and Luoma. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Kimmo Luoma, University of Turku, Turku, Finland
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