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Quantum reference frame transformations as symmetries and the paradox of the third particle

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arxiv 2011.01951 v2 pith:BXK23RXL submitted 2020-11-03 quant-ph gr-qcmath-phmath.MP

Quantum reference frame transformations as symmetries and the paradox of the third particle

classification quant-ph gr-qcmath-phmath.MP
keywords quantumparadoxparticlephysicalreferencesymmetriestransformationsframe
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved
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In a quantum world, reference frames are ultimately quantum systems too -- but what does it mean to "jump into the perspective of a quantum particle"? In this work, we show that quantum reference frame (QRF) transformations appear naturally as symmetries of simple physical systems. This allows us to rederive and generalize known QRF transformations within an alternative, operationally transparent framework, and to shed new light on their structure and interpretation. We give an explicit description of the observables that are measurable by agents constrained by such quantum symmetries, and apply our results to a puzzle known as the `paradox of the third particle'. We argue that it can be reduced to the question of how to relationally embed fewer into more particles, and give a thorough physical and algebraic analysis of this question. This leads us to a generalization of the partial trace (`relational trace') which arguably resolves the paradox, and it uncovers important structures of constraint quantization within a simple quantum information setting, such as relational observables which are key in this resolution. While we restrict our attention to finite Abelian groups for transparency and mathematical rigor, the intuitive physical appeal of our results makes us expect that they remain valid in more general situations.

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Cited by 7 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.

  1. How many degrees of freedom describe a quantum N-particle state?

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    Extends quantum reference frames to quantum reference fields in linearized quantum gravity and derives unitary maps implementing relational gauge-invariant observables between quantum perspectives.

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