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Quantum metrology with nonclassical states offers a promising route to improved precision in physical measurements. The quantum effects of Schr{\"o}dinger-cat superpositions or entanglements allow measurement uncertainties to reach below…

Quantum Physics · Physics 2025-07-11 Y. A. Yang , W. -T. Luo , J. -L. Zhang , S. -Z. Wang , Chang-Ling Zou , T. Xia , Z. -T. Lu

The Born rule for probabilities of measurement results is deduced from the set of five assumptions. The assumptions state that: (a) the state vector fully determines the probabilities of all measurement results; (b) between measurements,…

Quantum Physics · Physics 2013-08-27 Alexey V. Nenashev

We provide an affirmative answer to the question posed in the title. Our argument is based on a treatment of the Schroedinger dynamics of the composite of a quantum microsystem, S, and a macroscopic measuring apparatus, I, consisting of N…

Quantum Physics · Physics 2009-11-13 Geoffrey Sewell

It has recently been shown that it is possible to represent the complete quantum state of any system as a phase-space quasi-probability distribution (Wigner function) [Phys Rev Lett 117, 180401]. Such functions take the form of expectation…

Quantum Physics · Physics 2017-08-16 R. P. Rundle , P. W. Mills , Todd Tilma , J. H. Samson , M. J. Everitt

We provide optimal measurement schemes for estimating relative parameters of the quantum state of a pair of spin systems. We prove that the optimal measurements are joint measurements on the pair of systems, meaning that they cannot be…

Quantum Physics · Physics 2007-05-23 Stephen D. Bartlett , Terry Rudolph , Robert W. Spekkens

Pairs of spin-1/2 particles are prepared in a Werner state (namely, a mixture of singlet and random components). If the random component is large enough, the statistical results of spin measurements that may be performed on each pair…

Quantum Physics · Physics 2009-10-30 Asher Peres

The conventional view, that Einstein was wrong to believe that quantum physics is local and deterministic, is challenged. A parametrised model, Q, for the state vector evolution of spin 1/2 particles during measurement is developed. Q draws…

Quantum Physics · Physics 2008-02-03 T. N. Palmer

A scenario is outlined for quantum measurement, assuming that self-sustaining classicality is the consequence of an attractive gravitational self-interaction acting on massive bodies, and randomness arises already in the classical domain. A…

Quantum Physics · Physics 2007-05-23 Tamás Geszti

We implement Feynman's suggestion that the only missing notion needed for the puzzle of Quantum Measurement is the statistical mechanics of amplifying apparatus. We define a thermodynamic limit of quantum amplifiers which is a classically…

Quantum Physics · Physics 2007-05-23 Joseph Johnson

A small quantum scattering system (the microsystem) is studied in interaction with a large quantum system (the macrosystem) described by unknown stochastic variables. The interaction between the two systems is diagonal for the microsystem…

Quantum Physics · Physics 2007-05-23 Karl-Erik Eriksson

We present an exact derivation of a process in which a microscopic measured system interacts with heat-bath and pointer modes of a measuring device, via a coupling involving a general Hermitian operator $\Lambda$ of the system. In the limit…

Mesoscale and Nanoscale Physics · Physics 2016-08-31 Dima Mozyrsky , Vladimir Privman

The minimal memory required to model a given stochastic process - known as the statistical complexity - is a widely adopted quantifier of structure in complexity science. Here, we ask if quantum mechanics can fundamentally change the…

Quantum Physics · Physics 2017-08-28 Whei Yeap Suen , Jayne Thompson , Andrew J. P. Garner , Vlatko Vedral , Mile Gu

We demonstrate the role of measurement back-action of a coherent spin environment on the dynamics of a spin (qubit) coupled to it, by inducing non-classical (Quantum Random Walk like) statistics on its measurement trajectory. We show how…

Quantum Physics · Physics 2019-08-14 D. D. Bhaktavatsala Rao , Sen Yang , Stefan Jesenski , Florian Kaiser , Jörg Wrachtrup

A solution to the second measurement problem, determining what prior microscopic properties can be inferred from measurement outcomes ("pointer positions"), is worked out for projective and generalized (POVM) measurements, using consistent…

Quantum Physics · Physics 2017-09-20 Robert B. Griffiths

Cloning of observables, unlike standard cloning of states, aims at copying the information encoded in the statistics of a class of observables rather then on quantum states themselves. In such a process the emphasis is on the quantum…

Quantum Physics · Physics 2007-08-08 Alessandro Ferraro , Matteo G A Paris

This note starts with a recapitulation of what people call the ``Measurement Problem'' of Quantum Mechanics (QM). The dissipative nature of the quantum-mechanical time-evolution of averages of states over large ensembles of identical…

Quantum Physics · Physics 2026-03-27 Jürg Fröhlich , Alessandro Pizzo

Operator scrambling denotes the evolution of a simple operator into a complicated one (in the Heisenberg picture), which characterizes quantum chaos in many-body systems. More specifically, a simple operator evolves into a linear…

Quantum Physics · Physics 2019-06-04 Xiao-Liang Qi , Emily J. Davis , Avikar Periwal , Monika Schleier-Smith

The standard model of the quantum theory of measurement is based on an interaction Hamiltonian in which the observable-to-be-measured is multiplied with some observable of a probe system. This simple Ansatz has proved extremely fruitful in…

Quantum Physics · Physics 2009-10-30 Paul Busch , Pekka Lahti

We propose a critical dissipaive quantum metrology schemes for single parameter estimation which are based on a quantum probe consisting of coherently driven ensemble of $N$ spin-1/2 particles under the effect of squeezed, collective spin…

Quantum Physics · Physics 2023-08-16 Venelin P. Pavlov , Diego Porras , Peter A. Ivanov

Quantum entanglement is one of the core features of quantum theory. While it is typically revealed by measurements along carefully chosen directions, here we review different methods based on so-called random or randomized measurements.…

Quantum Physics · Physics 2020-11-24 Lukas Knips
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