Search results

1

Ehrenfest Theorem for the Hamilton-Jacobi Equation

100%

Kocis L.

Acta Physica Polonica A

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2002

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vol. 102

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issue 6

709-716

EN

A possible way from quantum mechanics to classical mechanics can be achieved with an exponential substitution used in the Schrödinger equation, and then considering the classical limit. This gives a picture of classical fluid and an ensemble of classical trajectories. In difference from this approach to the classical limit, while utilising the same substitution, we assume a minimum uncertainty wave packet. It is shown that this approach to the classical limit of quantum mechanics yields a single trajectory traced by the centroid of the minimum uncertainty wave packet. The momentum and the centroid of such packet satisfy the classical Hamilton-Jacobi equation.

2

Realistic Measurement of Phase

63%

Paul H., Leonhardt U.

Acta Physica Polonica A

|

1994

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vol. 86

|

issue 1

213-223

EN

The experimental schemes for measuring quantum-mechanical phase properties of light suggested and partly also realized thus far, namely (i) amplification, with the help of a quantum amplifier, of the microscopic field before phase measurement, (ii) heterodyning the field with a strong local oscillator, and (iii) performing two separate homodyne measurements on the field after beam splitting, are compared from a theoretical point of view. They share the common feature that undesired noise enters the experimental setup, which makes the measurement fuzzy. It will be pointed out that all three schemes amount to measuring the Q function of the original field, and hence are fully equivalent. Since the Q function can be interpreted as a smoothed Wigner function, one may associate with the introduced noise a smoothing process in which intrinsically quantum-mechanical features displayed by finer details of the Wigner function - especially by the occurrence of negative values - are lost. As a consequence, the measured phase distribution will be broader than the "true" one based on the concept of a quantum-mechanical phase operator. In realistic experiments, the nonunit detection efficiency further deteriorates the measuring results. It will be shown that also this effect can be properly described by an (additional) smoothing process leading to a certain s-parametrized quasiprobability distribution, with a parameter s that is connected with the detection efficiency in a simple way, as the distribution that is actually measurable.

3

Classical Limit of Entangled Correlations

63%

Wódkiewicz K.

Acta Physica Polonica A

|

1994

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vol. 86

|

issue 1

223-234

EN

Generalizations of Bell's inequalities for Einstein Podolsky and Rosen entangled correlations for arbitrary spin s are discussed. Violations of local realism and the classical limit of quantum nonlocality for large s are discussed. The role of the polarization and of the spin alignment in the violation of the Bell inequalities are investigated. A Bayes analysis of entangled correlations is performed using the nonlocal quantum distribution. The local but nonpositive Einstein Podolsky and Rosen quantum distribution is investigated in the limit when s → ∞. The classical limit of the quantum Malus law for arbitrary spin s is formulated in terms of the spin path integrals.

4

Equations of Motion for a Charged Particle in n-Dimensional Magnetic Field

63%

Florek W., Thomas M.

Acta Physica Polonica A

|

2000

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vol. 97

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issue 5

935-938

EN

The equation of motion for a charged particle moving in the n-dimensional constant magnetic field is obtained for any linear gauge and any metric tensor by generalization of Johnson and Lipmann's approach. It allows to consider the magnetic orbits in the n-dimensional space. It is shown that the movement of a particle can always be decomposed into a number of two-dimensional cyclotronic motions and a free particle part.

5

Application of the Mathematical Methods of the Braid Group Theory to Quantization of Many-Particle Systems

63%

Jacak D., Jacak L., Wieczorek K.

Acta Physica Polonica A

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1994

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vol. 85

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issue 3

483-496

EN

The problem of the non-standard statistics for one-, two- and three-dimensional systems of N identical particles on various manifolds is reviewed in terms of the braid group theory. The braid groups together with their unitary representations are studied for the line, circle, plane, sphere, torus and the three-dimensional Euclidean space. Nonequivalent quantizations of several physical systems are presented.

6

On Electrostatic Aharonov-Bohm Effect in Solids

63%

Figielski T., Wosiński T., Morawski A., Mąkosa A.

|

EN

We analyse conditions for an appearance of the electrostatic Aharonov- Bohm interference in two systems: a single-channel quantum-wire loop and an open ballistic quantum dot. We show that in the first system the effect will be destroyed by charge fluctuations, which probably is the reason why it has not been clearly observed, while in the second system the effect is still open for exploration.

7

Irreducible Basis for Permutation Representations

63%

Florek W.

Acta Physica Polonica A

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1999

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vol. 96

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issue 6

699-712

EN

For a given finite group G its permutation representation P, i.e. an action on an n-element set, is considered. Introducing a vector space L as a set of formal linear combinations of | j 〉, 1 ≤ j ≤ n, the representation P is linearized. In general, the representation obtained is reducible, so it is decomposed into irreducible components. Decomposition of L into invariant subspaces is determined by a unitary transformation leading from the basis { | j 〉} to a new, symmetry adapted or irreducible, basis { |Γrγ〉}. This problem is quite generally solved by means of the so-called Sakata matrix. Some possible physical applications are indicated.

8

Quantum States and Number-Phase Uncertainty Relations Measured by Optical Homodyne Tomography

63%

Raymer M. G., Smithey D. T., Beck M., Cooper J.

Acta Physica Polonica A

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1994

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vol. 86

|

issue 1

71-80

EN

Experiments have been performed to determine the Wigner distribution and the density matrix (and for pure states the wave function) of a light mode, by using tomographic inversion of a set of measured probability distributions for quadrature amplitudes. From these measurements the quantum distributions of optical phase and photon number have been obtained. The measurements of quadrature-amplitude distributions for a temporal mode of the electromagnetic field are carried out using balanced homodyne detection. We refer to this new method as optical homodyne tomography. Given the measured density matrix, one can experimentally infer any of the various quantum distributions of optical phase, in particular the Pegg-Barnett (or, equivalently, Shapiro-Shepard) phase distribution, the marginal Wigner distribution, and the Vogel-Schleich operational phase distribution. We have used this approach to make measurements of the number-phase uncertainty relation for coherent-state fields. The coherent states do not attain the minimum value for the number-phase uncertainty product, as set by the expectation value of the commutator of the number and phase operators; this is true theoretically and experimentally.

9

Against Quantum Noise

63%

Ekert A., Macchiavello C.

Acta Physica Polonica A

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1998

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vol. 93

|

issue 1

63-76

EN

This is a brief description of how to protect quantum states from dissipation and decoherence that arise due to uncontrolled interactions with the environment. We discuss recoherence and stabilization of quantum states based on two techniques known as "symmetrization" and "quantum error correction". We illustrate our considerations with the most popular quantum-optical model of the system-environment interaction, commonly used to describe spontaneous emission, and show the benefits of quantum error correction in this case.

10

Quantum Instabilities and Decoherence Problem

63%

Kilin S., Horoshko D., Shatokhin V.

Acta Physica Polonica A

|

1998

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vol. 93

|

issue 1

97-104

EN

A decoherence problem is discussed by means of quantum continuous measurement theory. It is shown that the conditional state of quantum system interacting with a bath preserves its initial purity. In this presentation decoherence arises as a result of averaging over the stochastic times of reduction moments ("clicks"). A method based on external phase feedback is proposed to slow down the decoherence of field superposition state in an open optical cavity. It is also shown that an atom placed inside the optical cavity plays a role of internal self-organized positive feedback between field and atom, which leads to an exponential increase in the mean dipole moment of the atom for the field initially prepared in a superposition of coherent states, i.e. to quantum instability.

11

Probing Higher Dimensions of Hilbert Space in Experiment

63%

Zeilinger A.

Acta Physica Polonica A

|

1994

|

vol. 85

|

issue 4

717-723

EN

Using the correlated pairs produced in spontaneous parametric down-conversion, one can extract quantum states effectively defined in a Hilbert space of any dimension N. Furthermore, using just beam splitters and phase shifters one can build any unitary operator in the laboratory. We briefly discuss how this can be done, what kind of states could easily be produced in the laboratory, and we will discuss one explicit result pertaining to photon bunching in an N-dimensional Hilbert space.

12

Aharonov-Bohm Effect at Misfit Dislocations in GaAsSb/GaAs Heterostructures

51%

Figielski T., Wosiński T., Mąkosa A., Dobrowolski W., Raczyńska J.

Acta Physica Polonica A

|

1996

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vol. 90

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issue 4

773-776

EN

We examined the current flowing through p^{+}-n junction of the lattice mismatched GaAs_{1-x}Sb_{x}/GaAs heterostructure in a transverse magnetic field at 1.8 K. We have found the appearance of current oscillations, periodic as a function of the magnetic field, that are due to the Aharonov-Bohm effect of holes passed around charged dislocations.

13

Measurement of Wave Fields

51%

Walmsley I., Waxer L., Iaconis C.

Acta Physica Polonica A

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1998

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vol. 93

|

issue 1

159-178

EN

Wave fields play a central role in both classical and quantum mechanics. Generally applicable methods for the characterization of (scalar) fields are outlined, and illustrated by experiment and simulation.

14

Quest for Ghz States

51%

Żukowski M., Zeilinger A., Horne M., Weinfurter H.

Acta Physica Polonica A

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1998

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vol. 93

|

issue 1

187-195

EN

The premises of the Einstein-Podolsky-Rosen argument for their claim that quantum mechanics is an incomplete theory are inconsistent when applied to three-particle systems in entangled Greenberger-Horne-Zeilinger states. However, thus far there is no experimental confirmation for existence of such states. We propose a technique to obtain Greenberger-Horne-Zeilinger states which rests upon an observation that when a single particle from two independent entangled pairs is detected in a manner such that it is impossible to determine from which pair the single came, the remaining three particles become entangled.

15

Control of Open Quantum Systems

51%

Japha Y., Kofman A., Kurizki G.

Acta Physica Polonica A

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1998

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vol. 93

|

issue 1

135-145

EN

Spontaneous decay of excited cold atoms into a cavity can drastically affect their translational dynamics, namely, atomic reflection, transmission and localization at the interface. We show that the quantum Zeno effect on excitation decay of an atom is observable in open cavities and waveguides, using a sequence of evolution-interrupting pulses on a nanosecond scale.

16

On entanglement distillation and quantum error correction for unknown states and channels

38%

Horodecki P.

Open Physics

|

2003

|

vol. 1

|

issue 4

695-707

EN

We consider the problem of invariance of distillable entanglement D and quantum capacities Q under erasure of information about single copy of quantum state or channel respectively. We argue that any 2 ⊗N two-way distillable state is still two-way distillable after erasure of single copy information. For some known distillation protocols the obtained two-way distillation rate is the same as if Alice and Bob knew the state from the very beginning. The isomorphism between quantum states and quantum channels is also investigated. In particular it is pointed out that any transmission rate down the channel is equal to distillation rate with formal LOCC-like superoperator that uses in general nonphysical Alice actions. This allows to we prove that if given channel Λ has nonzero capacity (Q → or Q ⟺) then the corresponding quantum state ϱ(Λ) has nonzero distillable entanglement (D → or D ⟺). Follwoing the latter arguments are provided that any channel mapping single qubit into N level system allows for reliable two-way transmission after erasure of information about single copy. Some open problems are discussed.

Refine search results

Ehrenfest Theorem for the Hamilton-Jacobi Equation

Realistic Measurement of Phase

Classical Limit of Entangled Correlations

Equations of Motion for a Charged Particle in n-Dimensional Magnetic Field

Application of the Mathematical Methods of the Braid Group Theory to Quantization of Many-Particle Systems

On Electrostatic Aharonov-Bohm Effect in Solids

Irreducible Basis for Permutation Representations

Quantum States and Number-Phase Uncertainty Relations Measured by Optical Homodyne Tomography

Against Quantum Noise

Quantum Instabilities and Decoherence Problem

Probing Higher Dimensions of Hilbert Space in Experiment

Aharonov-Bohm Effect at Misfit Dislocations in GaAsSb/GaAs Heterostructures

Measurement of Wave Fields

Quest for Ghz States

Control of Open Quantum Systems

On entanglement distillation and quantum error correction for unknown states and channels