Macroscopic Observables

@article{Poulin2004MacroscopicO,
  title={Macroscopic Observables},
  author={D. Poulin},
  journal={Physical Review A},
  year={2004}
}
  • D. Poulin
  • Published 2004
  • Physics
  • Physical Review A
We study macroscopic observables defined as the total value of a physical quantity over a collection of quantum systems. We show that previous results obtained for an infinite ensemble of identically prepared systems lead to incorrect conclusions for finite ensembles. In particular, exact measurement of a macroscopic observable significantly disturbs the state of any finite ensemble. However, we show how this disturbance can be made arbitrarily small when the measurements are of finite accuracy… Expand
Robust Macroscopic Quantum Measurements in the Presence of Limited Control and Knowledge
TLDR
This paper focuses on the task of the polarization direction estimation of a system of N spins 1/2 particles and investigates the model some of us proposed in Barnea et al., 2017, based on a von Neumann pointer measurement, and shows traits of a classical measurement for an intermediate coupling strength. Expand
Coherence, asymmetry, and quantum macroscopicity
We investigate a measure of quantum coherence and its extension to quantify quantum macroscopicity. The coherence measure can also quantify the asymmetry of a quantum state with respect to a givenExpand
Quantum averages of weak values
We re-examine the status of the weak value of a quantum mechanical observable as an objective physical concept, addressing its physical interpretation and general domain of applicability. We showExpand
Classical world arising out of quantum physics under the restriction of coarse-grained measurements.
TLDR
It is demonstrated that for unrestricted measurement accuracy, no classical description is possible for arbitrarily large systems and for a certain time evolution that under coarse-grained measurements, not only macrorealism but even classical Newtonian laws emerge out of the Schrödinger equation and the projection postulate. Expand
Conditions for quantum violation of macroscopic realism.
TLDR
There exist "nonclassical" Hamiltonians whose time evolution cannot be understood classically, although at every instant of time the quantum state appears as a classical mixture, and it is suggested that such Hamiltonians are unlikely to be realized in nature because of their high computational complexity. Expand
Quantum Models of Classical World
TLDR
This paper has two aims: a clear explanation of all new results and a coherent and contradiction-free account of the whole quantum mechanics including all necessary changes of its current textbook version. Expand
Correlations in local measurements and entanglement in many-body systems
While entanglement plays an important role in characterizing quantum many-body systems, it is hardly possible to directly access many-body entanglement in real experiments. In this paper, we studyExpand
Quantum Model of Classical Mechanics: Maximum Entropy Packets
In a previous paper, a statistical method of constructing quantum models of classical properties has been described. The present paper concludes the description by turning to classical mechanics. TheExpand
Disappearance of macroscopic superpositions in perfectly isolated systems by thermalization processes
Schr\"odinger's illustration of an imaginary cat in a box, neither alive nor dead, leads to a question of whether and how long a macroscopic quantum superposition can exist in various situations. ItExpand
Local realism of macroscopic correlations.
TLDR
It is argued that the emergence of local realism at the macroscopic level is caused by an interplay between the monogamous nature of quantum correlations and the fact that Macroscopic measurements do not reveal properties of individual particles. Expand
...
1
2
3
...

References

SHOWING 1-10 OF 21 REFERENCES
Consistent interpretations of quantum mechanics
Within the last decade, significant progress has been made towards a consistent and complete reformulation of the Copenhagen interpretation (an interpretation consisting in a formulation of theExpand
Fragility of a class of highly entangled states with n qubits
We consider a quantum computer with $n$ quantum bits (``qubits''), where each qubit is coupled independently to an environment affecting the state in a dephasing or depolarizing way. For mixed statesExpand
Decoherence, einselection, and the quantum origins of the classical
as quantum engineering. In the past two decades it has become increasingly clear that many (perhaps all) of the symptoms of classicality can be induced in quantum systems by their environments. ThusExpand
Consistent histories and the interpretation of quantum mechanics
The usual formula for transition probabilities in nonrelativistic quantum mechanics is generalized to yield conditional probabilities for selected sequences of events at several different times,Expand
Decoherent histories and hydrodynamic equations
For a system consisting of a large collection of particles, variables that will generally become effectively classical are the local densities (number, momentum, energy). That is, in the context ofExpand
Decoherent Histories and the Emergent Classicality of Local Densities
In the context of the decoherent histories approach to quantum theory, it is shown that a class of macroscopic configurations consisting of histories of local densities (number, momentum, energy)Expand
Logical reformulation of quantum mechanics. I. Foundations
The basic rules of quantum mechanics are reformulated. They deal primarily with individual systems and do not assume that every ket may represent a physical state. The customary kinematic and dynamicExpand
Unknown Quantum States: The Quantum de Finetti Representation
We present an elementary proof of the quantum de Finetti representation theorem, a quantum analog of de Finetti’s classical theorem on exchangeable probability assignments. This contrasts with theExpand
Quantum feedback with weak measurements
The problem of feedback control of quantum systems by means of weak measurements is investigated in detail. When weak measurements are made on a set of identical quantum systems, the single-systemExpand
NMR Based Quantum Information Processing: Achievements and Prospects
Nuclear magnetic resonance (NMR) provides an experimental setting to explore physical implementations of quantum information processing (QIP). Here we introduce the basic background for understandingExpand
...
1
2
3
...