Determining the quantum expectation value by measuring a single photon

Piacentini, Fabrizio; Avella, Alessio; Rebufello, Enrico; Lussana, Rudi; Villa, Federica; Tosi, Alberto; Gramegna, Marco; Brida, G.; Cohen, Eliahu; Vaidman, Lev; Degiovanni, I. P.

doi:10.1038/nphys4223

Cited by 50 publications

(72 citation statements)

References 32 publications

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“…This is reasonable, since the measurement device is macroscopic and can provide any amount of energy. As a final remark, notice that, in the numerical findings of Figure 3, the statistics of the quantum-heat fluctuations originated by the system respect the same ergodic hypothesis that is satisfied whenever a sequence of quantum measurements is performed on a quantum system [43][44][45]. In particular, in Figure 3, one can observe that the analytical expression of G( ) for a large M (i.e., in the asymptotic regime obtained by indefinitely increasing the time duration of the implemented protocol) practically coincides with the numerical results obtained by simulating a sequence with a finite number of measurements (M = 20) but over a quite large number (3 · 10 5 ) of realizations.…”

Section: Large M Limitmentioning

confidence: 59%

Quantum-Heat Fluctuation Relations in Three-Level Systems Under Projective Measurements

et al. 2020

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We study the statistics of energy fluctuations in a three-level quantum system subject to a sequence of projective quantum measurements. We check that, as expected, the quantum Jarzynski equality holds provided that the initial state is thermal. The latter condition is trivially satisfied for twolevel systems, while this is generally no longer true for N -level systems, with N > 2. Focusing on three-level systems, we discuss the occurrence of a unique energy scale factor β eff that formally plays the role of an effective inverse temperature in the Jarzynski equality. To this aim, we introduce a suitable parametrization of the initial state in terms of a thermal and a non-thermal component. We determine the value of β eff for a large number of measurements and study its dependence on the initial state. Our predictions could be checked experimentally in quantum optics.

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Section: Large M Limitmentioning

confidence: 59%

Quantum-Heat Fluctuation Relations in Three-Level Systems Under Projective Measurements

et al. 2020

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“…Another reason (discussed in [11,12]) for the TSVF being heuristically simple is the apparent implausibility of assigning a property to an ensemble of N 1 atoms based on a very few atoms 4λ 2 q 2 that went from ground to excited. We find it more natural to assign this property to each of the atoms individually (this was recently supported by [64]). In a recent series of papers [52][53][54], we have further advocated this view, based on a realistic and deterministic account of QM relying on the combination of two boundary conditions.…”

Section: Appendix A: Further Analysis In Terms Of Weak Measurementsmentioning

confidence: 99%

Interaction-Free Effects Between Distant Atoms

et al. 2017

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A Gedanken experiment is presented where an excited and a ground-state atom are positioned such that, within the former's half-life time, they exchange a photon with 50% probability. A measurement of their energy state will therefore indicate in 50% of the cases that no photon was exchanged. Yet other measurements would reveal that, by the mere possibility of exchange, the two atoms have become entangled. Consequently, the "no exchange" result, apparently precluding entanglement, is non-locally established between the atoms by this very entanglement. This quantum-mechanical version of the ancient Liar Paradox can be realized with already existing transmission schemes, with the addition of Bell's theorem applied to the no-exchange cases. Under appropriate probabilities, the initially-excited atom, still excited, can be entangled with additional atoms time and again, or alternatively, exert multipartite nonlocal correlations in an interaction free manner. When densely repeated several times, this result also gives rise to the Quantum Zeno effect, again exerted between distant atoms without photon exchange. We discuss these experiments as variants of interactionfree-measurement, now generalized for both spatial and temporal uncertainties. We next employ weak measurements for elucidating the paradox. Interpretational issues are discussed in the conclusion, and a resolution is offered within the Two-State Vector Formalism and its new Heisenberg framework.

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“…An experimental realization of a protective measurement using photons has been reported in Ref. [21].…”

Section: Introductionmentioning

confidence: 99%

Protective measurement of open quantum systems

Schlosshauer

2020

Phys. Rev. A

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We study protective quantum measurements in the presence of an environment and decoherence. We consider the model of a protectively measured qubit that also interacts with a spin environment during the measurement. We investigate how the coupling to the environment affects the two characteristic properties of a protective measurement, namely, (i) the ability to leave the state of the system approximately unchanged and (ii) the transfer of information about expectation values to the apparatus pointer. We find that even when the interaction with the environment is weak enough not to lead to appreciable decoherence of the initial qubit state, it causes a significant broadening of the probability distribution for the position of the apparatus pointer at the conclusion of the measurement. This washing out of the pointer position crucially diminishes the accuracy with which the desired expectation values can be measured from a readout of the pointer. We additionally show that even when the coupling to the environment is chosen such that the state of the system is immune to decoherence, the environment may still detrimentally affect the pointer readout.

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Determining the quantum expectation value by measuring a single photon

Cited by 50 publications

References 32 publications

Quantum-Heat Fluctuation Relations in Three-Level Systems Under Projective Measurements

Quantum-Heat Fluctuation Relations in Three-Level Systems Under Projective Measurements

Interaction-Free Effects Between Distant Atoms

Protective measurement of open quantum systems

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