Asymptotic State Transformations of Continuous Variable Resources

We study asymptotic state transformations in continuous variable quantum resource theories. In particular, we prove that monotones displaying lower semicontinuity and strong superadditivity can be used to bound asymptotic transformation rates in these settings. This removes the need for asymptotic c...

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Bibliographic Details
Published in:Communications in mathematical physics 2023, Vol.398 (1), p.291-351
Main Authors: Ferrari, Giovanni, Lami, Ludovico, Theurer, Thomas, Plenio, Martin B.
Format: Article
Language:English
Subjects:
Asymptotic properties
Classical and Quantum Gravitation
Complex Systems
Continuity (mathematics)
Entropy
Fock state
Free energy
Mathematical and Computational Physics
Mathematical Physics
Optical components
Physics
Physics and Astronomy
Quantum Physics
Relativity Theory
Theoretical
Transformations
Upper bounds
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Summary:We study asymptotic state transformations in continuous variable quantum resource theories. In particular, we prove that monotones displaying lower semicontinuity and strong superadditivity can be used to bound asymptotic transformation rates in these settings. This removes the need for asymptotic continuity, which cannot be defined in the traditional sense for infinite-dimensional systems. We consider three applications, to the resource theories of (I) optical nonclassicality, (II) entanglement, and (III) quantum thermodynamics. In cases (II) and (III), the employed monotones are the (infinite-dimensional) squashed entanglement and the free energy, respectively. For case (I), we consider the measured relative entropy of nonclassicality and prove it to be lower semicontinuous and strongly superadditive. One of our main technical contributions, and a key tool to establish these results, is a handy variational expression for the measured relative entropy of nonclassicality. Our technique then yields computable upper bounds on asymptotic transformation rates, including those achievable under linear optical elements. We also prove a number of results which guarantee that the measured relative entropy of nonclassicality is bounded on any physically meaningful state and easily computable for some classes of states of interest, e.g., Fock diagonal states. We conclude by applying our findings to the problem of cat state manipulation and noisy Fock state purification.
ISSN:0010-3616
1432-0916
DOI:10.1007/s00220-022-04523-6