In their strongest usage, quantum reference frames have been described as referring to"the measurements performed by a superposed lab","the perspective of a quantum particle","the point of view of a superposed observer", etc. While exciting, these operational proposals have remained brief and ambiguous, leading to misinterpretations and criticism. Here, we provide a detailed specification and defense of the notion of a position-superposed lab or observer. We argue that this requires no exotic claims about quantum physics and raises no greater interpretive difficulty than ordinary quantum measurements. We then derive several consequences of taking this operational meaning seriously. We stress that the position-superposed observers that define quantum references frames are different from, and considerably less problematic than, the outcome-superposed observers considered in Wigners'friend scenarios. In particular, we show that outcomes obtained by a position-superposed observer may (without decohering the superposition) be broadcast to a well-localised one, in contrast with Wigner's friend scenarios, which require the outcomes to remain internal to the system at hand. Finally, we defend the possibility to roleplay a quantum reference frame from a classical reference frame.
Quantum theory challenges the view that individual measurement outcomes are predefined and independent of the measurement context. Yet the quantum state itself -- the catalogue of probabilities for all possible measurements -- is usually assumed to be well defined. We argue that this assumption tacitly relies on measur...
Esteban Castro-Ruiz, Nathan Cohen, L. Barbado et al.· 0 citations
We generalize the notion of quantum reference frames (QRFs) to cases where the frame does not necessarily correspond to a tensor factor subsystem, but to a covariant quantum instrument. This unlocks a variety of physical applications:"frames of labeling"for indistinguishable particles, suggesting explanations for the s...
Stefan L. Ludescher, Manuel Mekonnen, Thomas D. Galley et al.· 1 citation
This doctoral dissertation on the foundations of quantum theory isolates and then formalizes a physically relevant concept that I have called"Epistemic Constraint."Here, epistemic constraints are the definite, intersubjectively agreeable, ordinary-language conditions under which experiments are described. The usual for...
We give an operational resolution of the third-particle paradox, relevant in the theory of quantum reference frames. The apparent paradox is that a system which is irrelevant in one quantum-reference-frame description can seem to become relevant after changing to another quantum reference frame, because the reduced sta...
Č. Brukner, Esteban Castro-Ruiz, Marius Krumm· 1 citation
When reference frames are treated quantum mechanically, the subsystem structure of quantum systems is no longer absolute, but depends on the choice of the quantum reference frame (QRF). This raises a basic question: which dynamical properties are preserved across QRFs, and which depend on the physical reference used to...
P. Luppi, Viktoria Kabel, Flaminia Giacomini et al.· 2 citations
Understanding a composite system through its constituents is a fundamental practice in physics. In the context of quantum reference frames (QRFs), however, combining the usual quantum-theoretic notion of composition with QRF perspectives gives rise to subtle issues, such as the'paradox of the third particle'. Here we s...
Bruna Sahdo, Esteban Castro-Ruiz· 0 citations
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