Relativistic Quantum Reference Frames: The Operational Meaning of Spin

Giacomini, Flaminia; Castro-Ruiz, Esteban; Brukner, Časlav

doi:10.1103/physrevlett.123.090404

Cited by 76 publications

(95 citation statements)

References 37 publications

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“…None of these systems include internal degrees of freedom. In forthcoming work [72], relativistic particles with spin will be incorporated into the original quantum reference frame approach of [1] and the operational consequences of quantum frame transformations will be explored in this setting.…”

Section: Discussionmentioning

confidence: 99%

“…In the previous section, we could equally well have chosen C as the reference system, starting with the respective expressions in the last lines of each of (24,25,72) and repeating the same steps by switching A and C labels. It is thus clear how to change from the internal perspective of quantum reference frame A to that of C via the perspective-neutral Dirac quantum theory: invert the transformations to A-perspective and apply the transformations to C-perspective.…”

Section: Switching Internal Perspectives In the Quantum Theorymentioning

confidence: 99%

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A change of perspective: switching quantum reference frames via a perspective-neutral framework

Vanrietvelde

Hoehn

Giacomini

et al. 2020

Quantum

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126

247

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Treating reference frames fundamentally as quantum systems is inevitable in quantum gravity and also in quantum foundations once considering laboratories as physical systems. Both fields thereby face the question of how to describe physics relative to quantum reference systems and how the descriptions relative to different such choices are related. Here, we exploit a fruitful interplay of ideas from both fields to begin developing a unifying approach to transformations among quantum reference systems that ultimately aims at encompassing both quantum and gravitational physics. In particular, using a gravity inspired symmetry principle, which enforces physical observables to be relational and leads to an inherent redundancy in the description, we develop a perspectiveneutral structure, which contains all frame perspectives at once and via which they are changed. We show that taking the perspective of a specific frame amounts to a fixing of the symmetry related redundancies in both the classical and quantum theory and that changing perspective corresponds to a symmetry transformation. We implement this using the language of constrained systems, which naturally encodes symmetries. Within a simple one-dimensional model, we recover some of the quantum frame transformations of [1], embedding them in a perspective-neutral framework. Using them, we illustrate how entanglement and classicality of an observed system depend on the quantum frame perspective. Our operational language also inspires a new interpretation of Dirac and reduced quantized theories as perspective-neutral and perspectival quantum theories, respectively, and reveals the link between them. In this light, we suggest a new take on the relation between a 'quantum general covariance' and the diffeomorphism symmetry in quantum gravity. * p.hoehn@univie.ac.at arXiv:1809.00556v2 [quant-ph]

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Section: Discussionmentioning

confidence: 99%

Section: Switching Internal Perspectives In the Quantum Theorymentioning

confidence: 99%

A change of perspective: switching quantum reference frames via a perspective-neutral framework

Vanrietvelde

Hoehn

Giacomini

et al. 2020

Quantum

Self Cite

126

247

View full text Add to dashboard Cite

show abstract

“…) is given by Equations ( 71) and (73). Thanks to the double superselection rule, this transformation preserves expectation values again per overlap of a σ 1 -with a σ 2 -sector, in obvious analogy to Equation (74).…”

Section: Observable Transformations In the Relational Heisenberg Picturementioning

confidence: 97%

Equivalence of Approaches to Relational Quantum Dynamics in Relativistic Settings

2021

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We have previously shown that three approaches to relational quantum dynamics—relational Dirac observables, the Page-Wootters formalism and quantum deparametrizations—are equivalent. Here we show that this “trinity” of relational quantum dynamics holds in relativistic settings per frequency superselection sector. Time according to a clock subsystem is defined via a positive operator-valued measure (POVM) that is covariant with respect to the group generated by its (quadratic) Hamiltonian. This differs from the usual choice of a self-adjoint clock observable conjugate to the clock momentum. It also resolves Kuchař's criticism that the Page-Wootters formalism yields incorrect localization probabilities for the relativistic particle when conditioning on a Minkowski time operator. We show that conditioning instead on the covariant clock POVM results in a Newton-Wigner type localization probability commonly used in relativistic quantum mechanics. By establishing the equivalence mentioned above, we also assign a consistent conditional-probability interpretation to relational observables and deparametrizations. Finally, we expand a recent method of changing temporal reference frames, and show how to transform states and observables frequency-sector-wise. We use this method to discuss an indirect clock self-reference effect and explore the state and temporal frame-dependence of the task of comparing and synchronizing different quantum clocks.

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“…For example, there is a recent interest in describing quantum systems in relation to reference frames that are themselves quantum. It is then necessary to explain how to jump from one such quantum reference system into another thereby creating quantum entanglement among the remaining constituents of the system [61][62][63][64][65][66]. In our case, the asymptotic shear σ(u, z,z) for a given Bondi frame (u, z,z) provides the classical frame of reference, the quantum variables are the gravitational edge modes, namely generators of horizontal diffeomorphisms (4.7) or boosts (4.30).…”

Section: Jhep04(2021)095mentioning

confidence: 99%

Null infinity as an open Hamiltonian system

Wieland

2021

J. High Energ. Phys.

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When a system emits gravitational radiation, the Bondi mass decreases. If the Bondi energy is Hamiltonian, it can thus only be a time-dependent Hamiltonian. In this paper, we show that the Bondi energy can be understood as a time-dependent Hamiltonian on the covariant phase space. Our derivation starts from the Hamiltonian formulation in domains with boundaries that are null. We introduce the most general boundary conditions on a generic such null boundary, and compute quasi-local charges for boosts, energy and angular momentum. Initially, these domains are at finite distance, such that there is a natural IR regulator. To remove the IR regulator, we introduce a double null foliation together with an adapted Newman-Penrose null tetrad. Both null directions are surface orthogonal. We study the falloff conditions for such specific null foliations and take the limit to null infinity. At null infinity, we recover the Bondi mass and the usual covariant phase space for the two radiative modes at the full non-perturbative level. Apart from technical results, the framework gives two important physical insights. First of all, it explains the physical significance of the corner term that is added in the Wald-Zoupas framework to render the quasi-conserved charges integrable. The term to be added is simply the derivative of the Hamiltonian with respect to the background fields that drive the time-dependence of the Hamiltonian. Secondly, we propose a new interpretation of the Bondi mass as the thermodynamical free energy of gravitational edge modes at future null infinity. The Bondi mass law is then simply the statement that the free energy always decreases on its way towards thermal equilibrium.

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Relativistic Quantum Reference Frames: The Operational Meaning of Spin

Cited by 76 publications

References 37 publications

A change of perspective: switching quantum reference frames via a perspective-neutral framework

A change of perspective: switching quantum reference frames via a perspective-neutral framework

Equivalence of Approaches to Relational Quantum Dynamics in Relativistic Settings

Null infinity as an open Hamiltonian system

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