Lower bounds on the size of general Schrödinger-cat states from experimental data

Fröwis, Florian

doi:10.1088/1751-8121/aa5a92

Cited by 9 publications

(12 citation statements)

References 50 publications

(98 reference statements)

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“…Meanwhile, these practical consequences directly lead to experimental means of verifying nonclassicality within a given system, without resorting to full tomography. Quantum Fisher information has also recently been adopted to quantify the macroscopicity of quantum systems [74,86,101]. This hints that, in capturing an operational form of nonclassicality for continuous-variable systems, we may naturally recover innate notions of macroscopic quantum effects.…”

Section: Discussionmentioning

confidence: 99%

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Operational Resource Theory of Continuous-Variable Nonclassicality

et al. 2018

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Genuinely quantum states of a harmonic oscillator may be distinguished from their classical counterparts by the Glauber-Sudarshan P-representation -a state lacking a positive P-function is said to be nonclassical. In this paper, we propose a general operational framework for studying nonclassicality as a resource in networks of passive linear elements and measurements with feed-forward. Within this setting, we define new measures of nonclassicality based on the quantum fluctuations of quadratures, as well as the quantum Fisher information of quadrature displacements. These lead to fundamental constraints on the manipulation of nonclassicality, especially its concentration into subsystems, that apply to generic multi-mode non-Gaussian states. Special cases of our framework include no-go results in the concentration of squeezing and a complete hierarchy of nonclassicality for single mode Gaussian states.

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Section: Discussionmentioning

confidence: 99%

“…[84]. Furthermore, F k is more directly accessible in experiments, there being a number of practical techniques for measuring and lowerbounding QFI [85][86][87].…”

Section: Metrology Monotonesmentioning

confidence: 99%

Operational Resource Theory of Continuous-Variable Nonclassicality

et al. 2018

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“…For a pure state four times the variance is equal to the QFI, so that a large quadrature variance directly implies high displacement sensitivity. The QFI has been also studied to quantify multipartite entanglement [47][48][49] and macroscopic quantum coherence [42,[50][51][52].…”

Section: (A) (Weak Monotonicity)mentioning

confidence: 99%

Nonclassicality as a Quantifiable Resource for Quantum Metrology

et al. 2019

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We establish the nonclassicality of continuous-variable states as a resource for quantum metrology. Based on the quantum Fisher information of multimode quadratures, we introduce the metrological power as a measure of nonclassicality with a concrete operational meaning of displacement sensitivity beyond the classical limit. This measure belongs to the resource theory of nonclassicality, which is nonincreasing under linear optical elements. Our Letter reveals that a single copy, highly nonclassical quantum state is intrinsically advantageous when compared to multiple copies of a quantum state with moderate nonclassicality. This suggests that metrological power is related to the degree of quantum macroscopicity. Finally, we demonstrate that metrological resources useful for nonclassical displacement sensing tasks can be always converted into a useful resource state for phase sensitivity beyond the classical limit. † n − α * nân ].

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“…Note that the quantum Fisher information plays a central role in one of the general proposals for macroscopic distinctness [14], so this measure is in some sense contained in the presented family as a limiting case. In particular, the insights we have about the quantum Fisher information can be used to apply our measure for small b to real experimental data [22].…”

Section: Direct Convex-roof Extension Of the MImentioning

confidence: 99%

“…bits of entanglement in the system. In the case of a channel  describing weak Gaussian noise from the environment, equation (22) shows that…”

Section: Noise As Measurement By Environmentmentioning

confidence: 99%

General measure for macroscopic quantum states beyond ‘dead and alive’

et al. 2018

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We consider the characterization of quantum superposition states beyond the pattern 'dead and alive'. We propose a measure that is applicable to superpositions of multiple macroscopically distinct states, superpositions with different weights as well as mixed states. The measure is based on the mutual information to characterize the distinguishability between the multiple branches of the superposition. This allows us to overcome limitations of previous proposals, and to bridge the gap between general measures for macroscopic quantumness and measures for Schrödinger-cat type superpositions. We discuss a number of relevant examples, provide an alternative definition using basis-dependent quantum discord and reveal connections to other proposals in the literature. Finally, we also show the connection between the size of quantum states as quantified by our measure and their vulnerability to noise.

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Lower bounds on the size of general Schrödinger-cat states from experimental data

Cited by 9 publications

References 50 publications

Operational Resource Theory of Continuous-Variable Nonclassicality

Operational Resource Theory of Continuous-Variable Nonclassicality

Nonclassicality as a Quantifiable Resource for Quantum Metrology

General measure for macroscopic quantum states beyond ‘dead and alive’

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