Quantum mechanics and the covariance of physical laws in quantum reference frames

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

doi:10.1038/s41467-018-08155-0

Cited by 219 publications

(420 citation statements)

References 49 publications

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“…This is different to the definition of such transformations given in Ref. [1], where the transformation is written as the classical reference frame transformation with the parameter of the transformation promoted to an operator, because the transformation of the spin degree of freedom alone does not correspond to a Lorentz boost. Notice, however, that the QRF transformation would be completely analogous to those in Ref.…”

Section: Acknowledgmentsmentioning

confidence: 80%

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Relativistic Quantum Reference Frames: The Operational Meaning of Spin

2019

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The spin is the prime example of a qubit. Encoding and decoding information in the spin qubit is operationally well defined through the Stern-Gerlach set-up in the non-relativistic (i.e., low velocity) limit. However, an operational definition of the spin in the relativistic regime is missing. The origin of this difficulty lies in the fact that, on the one hand, the spin gets entangled with the momentum in Lorentz-boosted reference frames, and on the other hand, for a particle moving in a superposition of velocities, it is impossible to "jump" to its rest frame, where spin is unambiguously defined. Here, we find a quantum reference frame transformation corresponding to a "superposition of Lorentz boosts," allowing us to transform to the rest frame of a particle that is in a superposition of relativistic momenta with respect to the laboratory frame. This enables us to first move to the particle's rest frame, define the spin measurements there (via the Stern-Gerlach experimental procedure), and then move back to the laboratory frame. In this way, we find a set of "relativistic Stern-Gerlach measurements" in the laboratory frame, and a set of observables satisfying the spin su(2) algebra. This operational procedure offers a concrete way of testing the relativistic features of the spin, and opens up the possibility of devising quantum information protocols for spin in the special-relativistic regime.arXiv:1811.08228v2 [quant-ph]

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Section: Acknowledgmentsmentioning

confidence: 80%

“…Another relevant property of the formalism for QRFs introduced in Ref. [1] is that the probability to observe an outcome of a measurement is conserved under change of QRF thanks to the unitarity of the QRF transformation. Specifically, if the probabilities in the QRF of C are calculated as…”

Section: Acknowledgmentsmentioning

confidence: 99%

Relativistic Quantum Reference Frames: The Operational Meaning of Spin

2019

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“…This means that to extend our explanation above for the Cherenkov effect here requires one to perform coordinate changes to quantum uncertain reference frames via quantum uncertain Lorentz transformations. A formalism of such quantum reference frames and related techniques are being developed, see, e.g., [35][36][37][38][39][40] and it will be natural to try to apply them to the Cherenkov-like effect here, that arises from coherent time evolutions of the center of mass, including coherent delocalization. The formalism of quantum reference frames may also be useful for taking into account relativistic effects, since it should allow us, for example, to hold the energy gap fixed in the detector's rest frame, even when the rest frame is quantum uncertain.…”

Section: Discussionmentioning

confidence: 99%

Coherent delocalization in the light-matter interaction

Stritzelberger

Kempf

2020

Phys. Rev. D

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We investigate how the coherent spreading of the center of mass wave function of a particle, such as an atom, molecule or ion, affects the particle's interaction with fields such as the electromagnetic field or a phonon field, in view also of possible applications to emerging quantum technologies. To this end, we develop a suitably generalized Unruh-deWitt model for the interaction between a delocalizing first quantized particle and a second quantized field. We study how the coherent spreading of the center of mass wave function of the particle affects emission and absorption rates and we find, in particular, that in the case of a supersonic coherent spreading in a medium, there should occur Cherenkov-like emissions, along with the excitation of the particle.

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“…where we have introduced the clock-switch operators P e±→t+ |p e e := |−|p e | t , P e±→t− |p e e := | |p e | t (2.41) in close analogy to [3] and the parity-swap operator of [1,41]. The quantum clock switch procedure can be summarized in a commutative diagram: and analogously for (2.38).…”

Section: )mentioning

confidence: 99%

Switching Internal Times and a New Perspective on the ‘Wave Function of the Universe’

Hoehn

2019

Universe

209

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Despite its importance in general relativity, a quantum notion of general covariance has not yet been established in quantum gravity and cosmology, where, given the a priori absence of coordinates, it is necessary to replace classical frames with dynamical quantum reference systems. As such, quantum general covariance bears on the ability to consistently switch between the descriptions of the same physics relative to arbitrary choices of quantum reference system. Recently, a systematic approach for such switches has been developed [1-3]. It links the descriptions relative to different choices of quantum reference system, identified as the correspondingly reduced quantum theories, via the reference-system-neutral Dirac quantization, in analogy to coordinate changes on a manifold. In this work, we apply this method to a simple cosmological model to demonstrate how to consistently switch between different internal time choices in quantum cosmology. We substantiate the argument that the conjunction of Dirac and reduced quantized versions of the theory defines a complete relational quantum theory that not only admits a quantum general covariance, but, we argue, also suggests a new perspective on the 'wave function of the universe'. It assumes the role of a perspective-neutral global state, without immediate physical interpretation, that, however, encodes all the descriptions of the universe relative to all possible choices of reference system at once and constitutes the crucial link between these internal perspectives. While, for simplicity, we use the Wheeler-DeWitt formulation, the method and arguments might be also adaptable to loop quantum cosmology.

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Quantum mechanics and the covariance of physical laws in quantum reference frames

Cited by 219 publications

References 49 publications

Relativistic Quantum Reference Frames: The Operational Meaning of Spin

Relativistic Quantum Reference Frames: The Operational Meaning of Spin

Coherent delocalization in the light-matter interaction

Switching Internal Times and a New Perspective on the ‘Wave Function of the Universe’

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