209 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
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
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
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
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
Maximal Accuracy and Minimal Disturbance in the Arthurs-Kelly Simultaneous Measurement Process
The accuracy of the Arthurs-Kelly model of a simultaneous measurement of
position and momentum is analysed using concepts developed by Braginsky and
Khalili in the context of measurements of a single quantum observable. A
distinction is made between the errors of retrodiction and prediction. It is
shown that the distribution of measured values coincides with the initial state
Husimi function when the retrodictive accuracy is maximised, and that it is
related to the final state anti-Husimi function (the P representation of
quantum optics) when the predictive accuracy is maximised. The disturbance of
the system by the measurement is also discussed. A class of minimally
disturbing measurements is characterised. It is shown that the distribution of
measured values then coincides with one of the smoothed Wigner functions
described by Cartwright.Comment: 12 pages, 0 figures. AMS-Latex. Earlier version replaced with final
published versio
Detection model based on representation of quantum particles by classical random fields: Born's rule and beyond
Recently a new attempt to go beyond quantum mechanics (QM) was presented in
the form of so called prequantum classical statistical field theory (PCSFT).
Its main experimental prediction is violation of Born's rule which provides
only an approximative description of real probabilities. We expect that it will
be possible to design numerous experiments demonstrating violation of Born's
rule. Moreover, recently the first experimental evidence of violation was found
in the triple slits interference experiment, see \cite{WWW}. Although this
experimental test was motivated by another prequantum model, it can be
definitely considered as at least preliminary confirmation of the main
prediction of PCSFT. In our approach quantum particles are just symbolic
representations of "prequantum random fields," e.g., "electron-field" or
"neutron-field"; photon is associated with classical random electromagnetic
field. Such prequantum fields fluctuate on time and space scales which are
essentially finer than scales of QM, cf. `t Hooft's attempt to go beyond QM
\cite{H1}--\cite{TH2}. In this paper we elaborate a detection model in the
PCSFT-framework. In this model classical random fields (corresponding to
"quantum particles") interact with detectors inducing probabilities which match
with Born's rule only approximately. Thus QM arises from PCSFT as an
approximative theory. New tests of violation of Born's rule are proposed.Comment: Relation with recent experiment on violation of Born's rule in the
triple slit experiment is discussed; new experimental test which might
confirm violation of Born's rule are presented (double stochsticity test and
interference magnitude test); the problem of "double clicks" is discusse
Pauli's Principle in Probe Microscopy
Exceptionally clear images of intramolecular structure can be attained in
dynamic force microscopy through the combination of a passivated tip apex and
operation in what has become known as the "Pauli exclusion regime" of the
tip-sample interaction. We discuss, from an experimentalist's perspective, a
number of aspects of the exclusion principle which underpin this ability to
achieve submolecular resolution. Our particular focus is on the origins,
history, and interpretation of Pauli's principle in the context of interatomic
and intermolecular interactions.Comment: This is a chapter from "Imaging and Manipulation of Adsorbates using
Dynamic Force Microscopy", a book which is part of the "Advances in Atom and
Single Molecule Machines" series published by Springer
[http://www.springer.com/series/10425]. To be published late 201
Preclinical evaluation of EpCAM-binding designed ankyrin repeat proteins (DARPins) as targeting moieties for bimodal near-infrared fluorescence and photoacoustic imaging of cancer
PURPOSE
Fluorescence-guided surgery (FGS) can play a key role in improving radical resection rates by assisting surgeons to gain adequate visualization of malignant tissue intraoperatively. Designed ankyrin repeat proteins (DARPins) possess optimal pharmacokinetic and other properties for in vivo imaging. This study aims to evaluate the preclinical potential of epithelial cell adhesion molecule (EpCAM)-binding DARPins as targeting moieties for near-infrared fluorescence (NIRF) and photoacoustic (PA) imaging of cancer.
METHODS
EpCAM-binding DARPins Ac2, Ec4.1, and non-binding control DARPin Off7 were conjugated to IRDye 800CW and their binding efficacy was evaluated on EpCAM-positive HT-29 and EpCAM-negative COLO-320 human colon cancer cell lines. Thereafter, NIRF and PA imaging of all three conjugates were performed in HT-29_luc2 tumor-bearing mice. At 24Â h post-injection, tumors and organs were resected and tracer biodistributions were analyzed.
RESULTS
Ac2-800CW and Ec4.1-800CW specifically bound to HT-29 cells, but not to COLO-320 cells. Next, 6 nmol and 24 h were established as the optimal in vivo dose and imaging time point for both DARPin tracers. At 24 h post-injection, mean tumor-to-background ratios of 2.60â±â0.3 and 3.1â±â0.3 were observed for Ac2-800CW and Ec4.1-800CW, respectively, allowing clear tumor delineation using the clinical Artemis NIRF imager. Biodistribution analyses in non-neoplastic tissue solely showed high fluorescence signal in the liver and kidney, which reflects the clearance of the DARPin tracers.
CONCLUSION
Our encouraging results show that EpCAM-binding DARPins are a promising class of targeting moieties for pan-carcinoma targeting, providing clear tumor delineation at 24Â h post-injection. The work described provides the preclinical foundation for DARPin-based bimodal NIRF/PA imaging of cancer
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