233 research outputs found
The Haroche-Ramsey experiment as a generalized measurement
A number of atomic beam experiments, related to the Ramsey experiment and a
recent experiment by Brune et al., are studied with respect to the question of
complementarity. Three different procedures for obtaining information on the
state of the incoming atom are compared. Positive operator-valued measures are
explicitly calculated. It is demonstrated that, in principle, it is possible to
choose the experimental arrangement so as to admit an interpretation as a joint
non-ideal measurement yielding interference and ``which-way'' information.
Comparison of the different measurements gives insight into the question of
which information is provided by a (generalized) quantum mechanical
measurement. For this purpose the subspaces of Hilbert-Schmidt space, spanned
by the operators of the POVM, are determined for different measurement
arrangements and different values of the parameters.Comment: REVTeX, 22 pages, 5 figure
Quantum state tomography using a single apparatus
The density matrix of a two-level system (spin, atom) is usually determined
by measuring the three non-commuting components of the Pauli vector. This
density matrix can also be obtained via the measurement data of two commuting
variables, using a single apparatus. This is done by coupling the two-level
system to a mode of radiation field, where the atom-field interaction is
described with the Jaynes--Cummings model. The mode starts its evolution from a
known coherent state. The unknown initial state of the atom is found by
measuring two commuting observables: the population difference of the atom and
the photon number of the field. We discuss the advantages of this setup and its
possible applications.Comment: 7 pages, 8 figure, Phys. Rev.
Joint measurements of spin, operational locality and uncertainty
Joint, or simultaneous, measurements of non-commuting observables are
possible within quantum mechanics, if one accepts an increase in the variances
of the jointly measured observables. In this paper, we discuss joint
measurements of a spin 1/2 particle along any two directions. Starting from an
operational locality principle, it is shown how to obtain a bound on how sharp
the joint measurement can be. We give a direct interpretation of this bound in
terms of an uncertainty relation.Comment: Accepted for publication in Phys. Rev.
Het vaststellen van de mate van religieuze tolerantie bij leraren in opleiding
In recent years, schools and education authorities worldwide have been paying increased attention to issues surrounding diversity and religious tolerance. Tolerance constitutes one of the most important preconditions for social justice, fairness and peaceful coexistence. Hence, the authors of this article decided to develop an instrument measuring the degree and nature of religious tolerance among student teachers. It is not this article’s purpose to enter into a discussion about how to actually resolve religious, cultural and political conflict, but merely to embark on the process of developing an instrument to measure the degree of religious tolerance among teachers and student teachers.Religious intolerance is increasingly viewed as problematic, and it appears that education has been assigned the role of inculcating religious tolerance in young people. Teachers are expected to be able to inculcate in their students the respect, empathy, critical thinking and acceptance of differences among people associated with the notion of tolerance. To be able to do this, teachers have to possess the traits of a tolerant person.Whether teachers are indeed tolerant in practice depends on the extent to which they have mastered the capacity to be tolerant. This article reports on a study that culminated in the construction of a questionnaire for measuring the degree to which students on the threshold of entering the teaching profession displayed a tolerant attitude.The construction of the questionnaire was based on a theoretical study of tolerance and intolerance. The questionnaire was then applied in three different countries (South Africa, the Netherlands and India). Factor analyses were performed on the data to establish the validity of the instrument. The first round of application revealed a number of shortcomings in the questionnaire. The study therefore recommends a revision of the questionnaire. Among other things, the factoral structure and the reliability of some of the sub-scales require further attention. The study ascribes the lower than expected explanation of variance in the data set to the cultural differences existing among the different groups of respondents in the three countries.The article closes by drawing a conclusion regarding the degree of religious tolerance among the respondents who participated in this first round of application of the questionnaire
Joint measurements and Bell inequalities
Joint quantum measurements of non-commuting observables are possible, if one
accepts an increase in the measured variances. A necessary condition for a
joint measurement to be possible is that a joint probability distribution
exists for the measurement. This fact suggests that there may be a link with
Bell inequalities, as these will be satisfied if and only if a joint
probability distribution for all involved observables exists. We investigate
the connections between Bell inequalities and conditions for joint quantum
measurements to be possible. Mermin's inequality for the three-particle
Greenberger-Horne-Zeilinger state turns out to be equivalent to the condition
for a joint measurement on two out of the three quantum systems to exist.
Gisin's Bell inequality for three co-planar measurement directions, meanwhile,
is shown to be less strict than the condition for the corresponding joint
measurement
On the Consequences of Retaining the General Validity of Locality in Physical Theory
The empirical validity of the locality (LOC) principle of relativity is used
to argue in favour of a local hidden variable theory (HVT) for individual
quantum processes. It is shown that such a HVT may reproduce the statistical
predictions of quantum mechanics (QM), provided the reproducibility of initial
hidden variable states is limited. This means that in a HVT limits should be
set to the validity of the notion of counterfactual definiteness (CFD). This is
supported by the empirical evidence that past, present, and future are
basically distinct. Our argumentation is contrasted with a recent one by Stapp
resulting in the opposite conclusion, i.e. nonlocality or the existence of
faster-than-light influences. We argue that Stapp's argumentation still depends
in an implicit, but crucial, way on both the notions of hidden variables and of
CFD. In addition, some implications of our results for the debate between Bohr
and Einstein, Podolsky and Rosen are discussed.Comment: revtex, 11 page
Brownian Entanglement
We show that for two classical brownian particles there exists an analog of
continuous-variable quantum entanglement: The common probability distribution
of the two coordinates and the corresponding coarse-grained velocities cannot
be prepared via mixing of any factorized distributions referring to the two
particles in separate. This is possible for particles which interacted in the
past, but do not interact in the present. Three factors are crucial for the
effect: 1) separation of time-scales of coordinate and momentum which motivates
the definition of coarse-grained velocities; 2) the resulting uncertainty
relations between the coordinate of the brownian particle and the change of its
coarse-grained velocity; 3) the fact that the coarse-grained velocity, though
pertaining to a single brownian particle, is defined on a common context of two
particles. The brownian entanglement is a consequence of a coarse-grained
description and disappears for a finer resolution of the brownian motion. We
discuss possibilities of its experimental realizations in examples of
macroscopic brownian motion.Comment: 18 pages, no figure
Quantum Locality
It is argued that while quantum mechanics contains nonlocal or entangled
states, the instantaneous or nonlocal influences sometimes thought to be
present due to violations of Bell inequalities in fact arise from mistaken
attempts to apply classical concepts and introduce probabilities in a manner
inconsistent with the Hilbert space structure of standard quantum mechanics.
Instead, Einstein locality is a valid quantum principle: objective properties
of individual quantum systems do not change when something is done to another
noninteracting system. There is no reason to suspect any conflict between
quantum theory and special relativity.Comment: Introduction has been revised, references added, minor corrections
elsewhere. To appear in Foundations of Physic
- …