共查询到20条相似文献,搜索用时 281 毫秒
1.
We use retrodictive quantum theory to analyse two-photon quantum imaging systems. The formalism is particularly suitable for calculating conditional probability distributions. 相似文献
2.
O. Jedrkiewicz R. Loudon J. Jeffers 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,39(1):129-140
Previous work on the retrodictive theory of direct
detection is extended to cover the homodyne detection of coherent optical
signal states
and
. The retrodictive input state probabilities are obtained by
the application of Bayes' theorem to the corresponding predictive
distributions, based on the probability operator measure (POM) elements for
the homodyne process. Results are derived for the retrodictive information
on the complex amplitude of the signal field obtainable from the difference
photocount statistics of both 4-port and 8-port balanced homodyne detection
schemes. The local oscillator is usually assumed much stronger than the
signal but the case of equal strengths in 4-port detection is also
considered. The calculated probability distributions and error rates are
illustrated numerically for values of signal and local oscillator strengths
that extend from the classical to the quantum regimes. 相似文献
3.
Bart D’Hooghe 《International Journal of Theoretical Physics》2010,49(12):3069-3084
We adopt an operational approach to quantum mechanics in which a physical system is defined by the mathematical structure
of its set of states and properties. We present a model in which the maximal change of state of the system due to interaction
with the measurement context is controlled by a parameter which corresponds with the number N of possible outcomes in an experiment. In the case N=2 the system reduces to a model for the spin measurements on a quantum spin-1/2 particle. In the limit N→∞ the system is classical, i.e. the experiments are deterministic and its set of properties is a Boolean lattice. For intermediate
situations the change of state due to measurement is neither ‘maximal’ (i.e. quantum) nor ‘zero’ (i.e. classical). We show
that two of the axioms used in Piron’s representation theorem for quantum mechanics are violated, namely the covering law
and weak modularity. Next, we discuss a modified version of the model for which it is even impossible to define an orthocomplementation
on the set of properties. Another interesting feature for the intermediate situations of this model is that the probability
of a state transition in general not only depends on the two states involved, but also on the measurement context which induces
the state transition. 相似文献
4.
We address the problem of information completeness of quantum measurements in connection to quantum state tomography and with particular concern to quantum symplectic tomography. We put forward some non-trivial situations where informatively incomplete set of tomograms allows as well the state reconstruction provided to have some a priori information on the state or its dynamics. We then introduce a measure of information completeness and apply it to symplectic quantum tomograms. 相似文献
5.
《Comptes Rendus Physique》2013,14(1):94-105
Here we review measurements of the normal and superconducting state properties of iron-based superconductors using high magnetic fields. We discuss the various physical mechanisms that limit superconductivity in high fields, and the information on the superconducting state that can be extracted from the upper critical field, but also how thermal fluctuations affect its determination by resistivity and specific heat measurements. We also discuss measurements of the normal state electronic structure focusing on measurement of quantum oscillations, particularly the de Haas–van Alphen effect. These results have determined very accurately, the topology of the Fermi surface and the quasi-particle masses in a number of different iron-based superconductors, from the 1111, 122 and 111 families. 相似文献
6.
D. M. Appleby 《International Journal of Theoretical Physics》1998,37(5):1491-1509
The concept of experimental accuracy isinvestigated in the context of the unbiased jointmeasurement processes defined by Arthurs and Kelly. Adistinction is made between the errors of retrodictionand prediction. Four error-disturbancerelationships are derived, analogous to the singleerror-disturbance relationship derived by Braginsky andKhalili in the context of single measurements ofposition only. A retrodictive and a predictive error-errorrelationship are also derived. The connection betweenthese relationships and the extended uncertaintyprinciple of Arthurs and Kelly is discussed. Thesimilarities and differences between the quantum mechanicaland classical concepts of experimental accuracy areexplored. It is argued that these relationships providegrounds for questioning Uffink's conclusion that the concept of a simultaneous measurement ofnoncommuting observables is not fruitful. 相似文献
7.
8.
9.
We propose an approach to connect components of a quantum computer by using a linear cluster state, with which an arbitrary N-particle state can be perfectly propagated between quantum components in two ways that are based on feedback measurements and local transformation. 相似文献
10.
Bart D’Hooghe 《Foundations of Physics》2010,40(11):1669-1680
In the foundations of quantum mechanics Gleason’s theorem dictates the uniqueness of the state transition probability via
the inner product of the corresponding state vectors in Hilbert space, independent of which measurement context induces this
transition. We argue that the state transition probability should not be regarded as a secondary concept which can be derived
from the structure on the set of states and properties, but instead should be regarded as a primitive concept for which measurement
context is crucial. Accordingly, we adopt an operational approach to quantum mechanics in which a physical entity is defined
by the structure of its set of states, set of properties and the possible (measurement) contexts which can be applied to this
entity. We put forward some elementary definitions to derive an operational theory from this State–COntext–Property (SCOP)
formalism. We show that if the SCOP satisfies a Gleason-like condition, namely that the state transition probability is independent
of which measurement context induces the change of state, then the lattice of properties is orthocomplemented, which is one
of the ‘quantum axioms’ used in the Piron–Solèr representation theorem for quantum systems. In this sense we obtain a possible
physical meaning for the orthocomplementation widely used in quantum structures. 相似文献
11.
12.
We study theoretically the properties of two Bose-Einstein condensates in different spin states, represented by a double Fock state. Individual measurements of the spins of the particles are performed in transverse directions, giving access to the relative phase of the condensates. Initially, this phase is completely undefined, and the first measurements provide random results. But a fixed value of this phase rapidly emerges under the effect of the successive quantum measurements, giving rise to a quasiclassical situation where all spins have parallel transverse orientations. If the number of measurements reaches its maximum (the number of particles), quantum effects show up again, giving rise to violations of Bell type inequalities. The violation of Bell-Clauser-Horne-Shimony-Holt inequalities with an arbitrarily large number of spins may be comparable (or even equal) to that obtained with two spins. 相似文献
13.
Fink JM Steffen L Studer P Bishop LS Baur M Bianchetti R Bozyigit D Lang C Filipp S Leek PJ Wallraff A 《Physical review letters》2010,105(16):163601
The quantum properties of electromagnetic, mechanical or other harmonic oscillators can be revealed by investigating their strong coherent coupling to a single quantum two level system in an approach known as cavity quantum electrodynamics (QED). At temperatures much lower than the characteristic energy level spacing the observation of vacuum Rabi oscillations or mode splittings with one or a few quanta asserts the quantum nature of the oscillator. Here, we study how the classical response of a cavity QED system emerges from the quantum one when its thermal occupation-or effective temperature-is raised gradually over 5 orders of magnitude. In this way we explore in detail the continuous quantum-to-classical crossover and demonstrate how to extract effective cavity field temperatures from both spectroscopic and time-resolved vacuum Rabi measurements. 相似文献
14.
Run-hua Shi Liu-sheng Huang Wei Yang Hong Zhong 《International Journal of Theoretical Physics》2011,50(11):3329-3336
We present an efficient symmetric scheme for five-party quantum state sharing of an arbitrary m-qubit state with 2m three-particle entangled states. The implementations of this scheme only need to exploit the CNOT gate operations and the
single-particle measurements, instead of the three-particle GHZ-state measurements, which makes it more convenient in a practical
application than some previous schemes. In addition, its total efficiency can approach the maximal value in theory. 相似文献
15.
We provide a general dynamical approach for the quantum Zeno and anti-Zeno efects in an open quantum system under repeated non-demolition measurements.In our approach the repeated measurements are described by a general dynamical model without the wave function collapse postulation.Based on that model,we further study both the short-time and long-time evolutions of the open quantum system under repeated non-demolition measurements,and derive the measurement-modified decay rates of the excited state.In the cases with frequent ideal measurements at zero-temperature,we re-obtain the same decay rate as that from the wave function collapse postulation(Nature,2000,405:546).The correction to the ideal decay rate is also obtained under the non-ideal measurements.Especially,we find that the quantum Zeno and anti-Zeno efects are possibly enhanced by the non-ideal natures of measurements.For the open system under measurements with arbitrary period,we generally derive the rate equation for the long-time evolution for the cases with arbitrary temperature and noise spectrum,and show that in the long-time evolution the noise spectrum is efectively tuned by the repeated measurements.Our approach is also able to describe the quantum Zeno and anti-Zeno efects given by the phase modulation pulses,as well as the relevant quantum control schemes. 相似文献
16.
We provide a general dynamical approach for the quantum Zeno and anti-Zeno efects in an open quantum system under repeated non-demolition measurements.In our approach the repeated measurements are described by a general dynamical model without the wave function collapse postulation.Based on that model,we further study both the short-time and long-time evolutions of the open quantum system under repeated non-demolition measurements,and derive the measurement-modified decay rates of the excited state.In the cases with frequent ideal measurements at zero-temperature,we re-obtain the same decay rate as that from the wave function collapse postulation(Nature,2000,405:546).The correction to the ideal decay rate is also obtained under the non-ideal measurements.Especially,we find that the quantum Zeno and anti-Zeno efects are possibly enhanced by the non-ideal natures of measurements.For the open system under measurements with arbitrary period,we generally derive the rate equation for the long-time evolution for the cases with arbitrary temperature and noise spectrum,and show that in the long-time evolution the noise spectrum is efectively tuned by the repeated measurements.Our approach is also able to describe the quantum Zeno and anti-Zeno efects given by the phase modulation pulses,as well as the relevant quantum control schemes. 相似文献
17.
M. Ban 《International Journal of Theoretical Physics》2007,46(1):184-192
The quantum retrodiction for open systems which obey the quantum Markovian dynamics is investigated by means of non-equilibrium
thermo Field dynamics (NETFD) which can easily derive the retrodictive time-evolution generators. NETFD can formulate the
quantum retrodiction for open systems in the same way as that for closed systems. 相似文献
18.
Approximate Real–Time Visualization of a Quantum Transition by Means of Continuous Fuzzy Measurement
Jürgen Audretsch Thomas Konrad Michael Mensky 《General Relativity and Gravitation》2001,33(7):1165-1180
For the detection of gravitational waves the quantum mechanical properties of the detector have to be taken into account. Not all gravitational wave detectors allow a quantum nondemolition (QND) measurement. Continuous weak or fuzzy measurements are an alternative to study the evolution of a quantum mechanical system under the influence of an external field. In the present paper we investigate this alternative by applying it to a simplified system. We numerically simulate continuous fuzzy measurements of the oscillations of a two-level atom subjected to a resonant external light field. We thereby address the question whether it is possible to measure characteristic features of the evolution of a single quantum system in real time without relying on a QND scheme. We compare two schemes of continuous measurement: continuous measurement with constant fuzziness and with fuzziness changing in the course of the measurement. Because the sensitivity of the two-level atom to the influence of the measurement depends on the state of the atom, it is possible to optimize the continuous fuzzy measurement by varying its fuzziness. 相似文献
19.
Subir Sachdev 《Pramana》2002,58(2):285-292
We discuss the possibility of spin-glass order in the vicinity of the unexpected metallic state of the two-dimensional electron
gas in zero applied magnetic field. An average ferromagnetic moment may also be present, and the spin-glass order then resides
in the plane orthogonal to the ferromagnetic moment. We argue that a quantum transition involving the destruction of the spinglass
order in an applied in-plane magnetic field offers a natural explanation of some features of recent magnetoconductance measurements.
We present a quantum field theory for such a transition and compute its mean field properties. 相似文献
20.
In the archetypal strongly correlated electron superconductor CeCu2Si2 and its Ge-substituted alloys CeCu2(Si1-xGex)2 two quantum phase transitions--one magnetic and one of so far unknown origin-can be crossed as a function of pressure. We examine the associated anomalous normal state by detailed measurements of the low temperature resistivity (rho) power-law exponent alpha. At the lower critical point (at pcl, 1相似文献