Gaussian discriminating strength

Rigovacca, L.; Farace, Alessandro; Pasquale, Antonella De; Giovannetti, Vittorio

doi:10.1103/physreva.92.042331

Cited by 25 publications

(31 citation statements)

References 56 publications

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“…The relevance of the sentence "and it alone" must be stressed: indeed, the work done in the second half of the last century on the N → ∞ limit of quantum theories is quite comprehensive but it neglects the case when the large-N system is the big partner of a principal quantum system, that only indirectly experiences such limit. This is, however, an exemplary situation in quantum technologies and OQS, hence the questions asked at the beginning of this Introduction have recently been formulated in the corresponding framework [1][2][3][9][10][11][12][13][14][15][16].…”

Section: Introductionmentioning

confidence: 99%

Whenever a quantum environment emerges as a classical system, it behaves like a measuring apparatus

Foti

Heinosaari

Maniscalco

et al. 2019

Quantum

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We study the dynamics of a quantum system Γ with an environment Ξ made of N elementary quantum components. We aim at answering the following questions: can the evolution of Γ be characterized by some general features when N becomes very large, regardless of the specific form of its interaction with each and every component of Ξ? In other terms: should we expect all quantum systems with a macroscopic environment to undergo a somehow similar evolution? And if yes, of what type? In order to answer these questions we use well established results from large-N quantum field theories, particularly referring to the conditions ensuring a large-N quantum model to be effectively described by a classical theory. We demonstrate that the fulfillment of these conditions, when properly imported into the framework of the open quantum systems dynamics, guarantees that the evolution of Γ is always of the same type of that expected if Ξ were a measuring apparatus, no matter the details of the actual interaction. On the other hand, such details are found to determine the specific basis w.r.t. which Γ undergoes the decoherence dictated by the dynamical description of the quantum measurement process. This result wears two hats: on the one hand it clarifies the physical origin of the formal statement that, under certain conditions, any channel from ρ Γ to ρ Ξ takes the form of a measure-and-prepare map, as recently shown in Ref. [1]; on the other hand, it for-Caterina Foti: caterina.foti@unifi.it malizes the qualitative argument that the reason why we do not observe state superpositions is the continual measurement performed by the environment.

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Section: Introductionmentioning

confidence: 99%

Whenever a quantum environment emerges as a classical system, it behaves like a measuring apparatus

Foti

Heinosaari

Maniscalco

et al. 2019

Quantum

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“…This task bears some analogy with the black box metrology protocol discussed in Section 4.2.1, indeed both settings provide direct operational interpretations for QCs quantifiers in worst case scenarios, with the difference that there the goal was to estimate the parameter imprinted by a local unitary U A on the probe subsystem A, while here the goal is just to determine whether a local unitary U A was applied or not to the probe subsystem A. This task has also been considered in continuous variable systems in [199] by restricting ρ AB and U A to Gaussian states and operations, respectively.…”

Section: (I)mentioning

confidence: 99%

“…(121). In continuous variable systems, the discriminating strength was investigated in [199] by restricting to a minimisation over Gaussian unitaries, and a closed expression was derived for a subclass of two-mode Gaussian states, exploiting the analytical formula for the quantum Chernoff distance between a pair of two-mode Gaussian states obtained in [200].…”

Section: Chernoff Distancementioning

confidence: 99%

Measures and applications of quantum correlations

Adesso¹,

Bromley²,

Cianciaruso³

2016

J. Phys. A: Math. Theor.

361

401

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Abstract. Quantum information theory is built upon the realisation that quantum resources like coherence and entanglement can be exploited for novel or enhanced ways of transmitting and manipulating information, such as quantum cryptography, teleportation, and quantum computing. We now know that there is potentially much more than entanglement behind the power of quantum information processing. There exist more general forms of non-classical correlations, stemming from fundamental principles such as the necessary disturbance induced by a local measurement, or the persistence of quantum coherence in all possible local bases. These signatures can be identified and are resilient in almost all quantum states, and have been linked to the enhanced performance of certain quantum protocols over classical ones in noisy conditions. Their presence represents, among other things, one of the most essential manifestations of quantumness in cooperative systems, from the subatomic to the macroscopic domain. In this work we give an overview of the current quest for a proper understanding and characterisation of the frontier between classical and quantum correlations in composite states. We focus on various approaches to define and quantify general quantum correlations, based on different yet interlinked physical perspectives, and comment on the operational significance of the ensuing measures for quantum technology tasks such as information encoding, distribution, discrimination and metrology. We then provide a broader outlook of a few applications in which quantumness beyond entanglement looks fit to play a key role.

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“…On the other hand, in the second half of this paper we also study the effects of a noisy encoding operation, moving away from the most common unitary setting. It is worth stressing that in all previous studies of Gaussian black-box metrology, the set of possible encoding Hamiltonians has been obtained by applying a generic Gaussian unitary operation to a harmonic Hamiltonian [28][29][30]. Although this choice represents the Gaussian equivalent of a generic change of basis in the finite-dimensional domain, it has the disadvantage of introducing energy into the probe, at random and for free.…”

Section: Introductionmentioning

confidence: 99%

“…Up to now only the former of the two aforementioned approaches to black-box metrology (i.e., guaranteeing minimal performances) has been investigated in the framework of Gaussian states and operations [25][26][27], and quantum discord has once again been identified as the important figure of merit for these discrimination tasks [28][29][30].…”

Section: Introductionmentioning

confidence: 99%

Versatile Gaussian probes for squeezing estimation

et al. 2017

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We consider an instance of "black-box" quantum metrology in the Gaussian framework, where we aim to estimate the amount of squeezing applied on an input probe, without previous knowledge on the phase of the applied squeezing. By taking the quantum Fisher information (QFI) as the figure of merit, we evaluate its average and variance with respect to this phase in order to identify probe states that yield good precision for many different squeezing directions. We first consider the case of single-mode Gaussian probes with the same energy, and find that pure squeezed states maximize the average quantum Fisher information (AvQFI) at the cost of a performance that oscillates strongly as the squeezing direction is changed. Although the variance can be brought to zero by correlating the probing system with a reference mode, the maximum AvQFI cannot be increased in the same way. A different scenario opens if one takes into account the effects of photon losses: coherent states represent the optimal single-mode choice when losses exceed a certain threshold and, moreover, correlated probes can now yield larger AvQFI values than all single-mode states, on top of having zero variance.

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Gaussian discriminating strength

Cited by 25 publications

References 56 publications

Whenever a quantum environment emerges as a classical system, it behaves like a measuring apparatus

Whenever a quantum environment emerges as a classical system, it behaves like a measuring apparatus

Measures and applications of quantum correlations

Versatile Gaussian probes for squeezing estimation

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