Non-ideal Measurement Research Articles

Quantum Zeno effect in non-ideal measurement processes(Quantum Field Theories: Fundamental Problems and Applications)

Quantum Zeno effect in non-ideal measurement processes(Quantum Field Theories: Fundamental Problems and Applications)

Non-ideal monitoring of a qubit state using a quantum tunnelling device

We propose a model for non-ideal monitoring of the state of a coupled quantum dot qubitby a quantum tunnelling device. The non-ideality is modelled using an equivalentmeasurement circuit. This allows realistically available measurement results tobe related to the state of the quantum system (qubit). We present a quantumtrajectory that describes the stochastic evolution of the qubit state conditioned bytunnelling events (i.e. current) through the device. We calculate and compare thenoise power spectra of the current in an ideal and a non-ideal measurement. Theresults show that when the two qubit dots are strongly coupled the non-idealmeasurement cannot detect the qubit state precisely. The limitation of the idealmodel for describing a realistic system may be estimated from the noise spectra.

Quantum Parallelism in Quantum Information Processing

We investigate distinguishability (measured by fidelity) of the initial and the final state of a qubit, which is an object of the so-called nonideal quantum measurement of the first kind. We show that the fidelity of a nonideal measurement can be greater than the fidelity of the corresponding ideal measurement. This result is somewhat counterintuitive, and can be traced back to the quantum parallelism in quantum operations, in analogy with the quantum parallelism manifested in the quantum computing theory. In particular, as the quantum parallelism in quantum computing underlies efficient quantum algorithms, the quantum parallelism in quantum information theory underlies the classically unexpected increase of fidelity.

Contrast-enhanced near-infrared laser mammography with a prototype breast scanner: feasibility study with tissue phantoms and preliminary results of imaging experimental tumors.

Near-infrared (NIR) optical mammography without contrast has a low specificity. The application of optical contrast medium may improve the performance. The concentration-dependent detectability of a new NIR contrast medium was determined with a prototype optical breast scanner. In vivo imaging of experimental tumors was performed. The NIR contrast agent NIR96010 is a newly synthesized, hydrophilic contrast agent for NIR mammography. A concentration-dependent contrast resolution was determined for tissue phantoms consisting of whole milk powder and gelatin. A central part of the phantoms measuring 2 x 2 cm2 without contrast was replaced with phantom material containing 1 micromol/L to 25 nmol/L NIR96010. The composite phantoms were measured with a prototype NIR breast scanner with lasers of lambda1 = 785 nm and lambda2 = 850 nm wavelength. Intensity profiles and standard deviations of the transmission signal in areas with and without contrast were determined by linear fit procedures. Signal-to-noise ratios and spatial resolution as a function of contrast concentration were determined. Near-infrared imaging of five tumor-bearing SCID mice (MX1 breast adenocarcinoma, tumor diameter 5-10 mm) was performed before and after intravenous application of 2 micromol/kg NIR96010. Spectrometry showed an absorption maximum of the contrast agent at 755 nm. No spectral shifts occurred in protein-containing solution. Signal-to-noise ratio in the transmission intensity profiles ranged from 1.1 at 25 nmol/L contrast to 28 at 1 micromol/L. At concentrations <40 nmol/L, no differentiation from the background was possible. The transitional area between the contrast-free edge of the phantom and the central contrast-containing part appeared in the profiles as a steep increase with a width of 4.2 +/- 1.8 mm. The experimental tumors were detectable in nonenhanced images as well as contrast-enhanced images, with better delineation after contrast administration. In postcontrast absorption profiles, a 44.1% +/- 11.3% greater absorption increase was seen in tumor tissue compared with normal tissue. The laser wavelength lambda1 of the prototype laser mammography device was not situated at maximum absorption of the contrast agent NIR96010 but on the descending shoulder of the absorption spectrum. This implies a 20% signal loss for contrast detection. Despite the nonideal measurement conditions, concentrations as low as 40 nmol/L were detectable in vitro. In vivo, all tumors were detectable in color-coded nonenhanced scans as well as in contrast-enhanced scans, with better delineation after contrast administration.

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.

Comparison of CFD simulations to experiment for convective heat transfer in a gas–solid fixed bed

Computational fluid dynamics (CFD) studies can improve understanding of fixed bed fluid flow and heat transfer. Our long-term objective is to use the CFD results in the development of tractable reactor models that are based on a good understanding of the fluid flow phenomena. The CFD simulations of fluid flow and heat transfer require verification to increase confidence in their use for model development. Results of a quantitative comparison between CFD results and heat transfer experimental data are given here. Simulations are presented for a model geometry of 44 solid spheres in a tube with tube-to-particle diameter ratio equal to 2. Velocity vector profiles and temperature contours have been obtained with emphasis on the wall–particle region. Comparisons are made with measured temperature profiles in a typical experimental setup with the same geometry. Several correction factors were required to compensate for non-ideal experimental measurements, and for phenomena that were not included in the CFD model. After correction, excellent agreement could be obtained between simulation and experiment.

Characterization of geometrical detection-system properties for two-dimensional tomography

Quantities that characterize the three-dimensional geometrical properties of detection systems for two-dimensional tomography are reviewed and compared. It is discussed how the quantities can be calculated and how they can be measured, including a measuring technique that uses a parallel laser beam. In many detection systems the finite detector size and the finite sizes of bounding apertures are not negligible, and these result in instrument functions with finite widths. Line-integral measurements are referred to as ideal measurements, whereas measurements by systems with instrument functions with finite width are nonideal. The quantities discussed make it possible to take into account these finite sizes in several tomography algorithms. If the spacing between adjacent lines of sight is much smaller than the widths of the instrument functions, the ideal measurements can be approximately reconstructed from the nonideal measurements. Such a reconstruction has been applied to bolometer measurements in a high plasma-density discharge in the Joint European Torus tokamak by sweeping the plasma in front of the bolometer detectors. The sweeping creates many extra virtual lines of sight and thus increases the resolution of the measurements close to the X point, where in high-density plasmas a peak in the radiation is found.

Nonideal measurement locations in planar near-field antenna metrology

Nonideal measurement locations in planar near-field antenna metrology

Near-field antenna measurements using nonideal measurement locations

We introduce a near-field to far-field transformation algorithm that relaxes the usual restriction that data points be located on a plane rectangular grid. Computational complexity is O(Nlog N) where N is the number of data points. This algorithm allows efficient processing of near-field data with known probe position errors. Also, the algorithm is applicable to other measurement approaches such as plane-polar scanning, where data are collected intentionally on a nonrectangular grid.

Some maximality results for effect-valued measures

We give an approach to the theory of effect-valued measures taking their values in the positive operators on a Hubert space. The concept of operator-valued measure is fundamental in modern theories of quantum measurements. In the paper we introduce and study relations of dominance and equivalence between two effect-valued measures and concepts of maximal and minimal effect-valued measures. Characterizations of maximal effect-valued measures are obtained in the discrete case and in the case of commutative range. As an example we study the so-called Bargmann measure which can be interpreted as a simultaneous non-ideal measurement of position and momentum.

Measurement and the Justification of the Statistical Postulate in Bohm's Causal Interpretation of Quantum Mechanics

I briefly sketch Bohm's causal interpretation (BCI) and its solution to the measurement problem. Crucial to BCI's no-collapse account of both ideal and non-ideal measurement is the existence of particles in addition to wavefunctions. The particles in their role as the producers of the observable experimental outcomes render practical considerations, such as what observables can be reasonably measured or how to get rid of interference terms in non-ideal measurements, secondary to BCI's account of measurement. I then explain why it is not easy for BCI to justify its statistical postulate. To successfully justify the postulate would be to solve the distribution problem. Two proposed deterministic solutions to this problem are only briefly set out and not discussed in detail. BCI can solve the measurement problem whether or not the distribution problem is solved. However, if the distribution problem is not solved, BCI cannot be shown to be empirically adequate.

Modal interpretations, decoherence and measurements

We address Albert and Loewer's criticism of non-ideal measurements in the modal interpretation, by examining the implications of the theory of decoherence for the modal interpretation. In the models originally considered by Albert and Loewer, the inclusion of decoherence provides an answer to their criticism. New problems seem to arise in different models and in situations more general than measurements.

Bell's Inequalities and Density Matrices: Revealing "Hidden" Nonlocality.

As is well known, quantum mechanical behavior cannot, in general, be simulated by a local hidden variables model. Most -if not all- the proofs of this incompatibility refer to the correlations which arise when each of two (or more) systems separated in space is subjected to a single ideal measurement. This setting is good enough to show contradictions between local hidden variables models and quantum mechanics in the case of pure states. However, as shown here, it is not powerful enough in the case of mixtures. This is illustrated by an example. In this example, the correlations which arise when each of two systems separated in space is subjected to a single ideal measurement are classical; only when each system is subjected to a {\it sequence} of ideal measurements non-classical correlations are obtained. We also ask whether there are situations for which even this last procedure is not powerful enough and non-ideal measurements have to be considered as well.

Measurement and the interpretation of quantum mechanics and relativity theory

The axiomatic approaches of quantum mechanics and relativity theory are compared with approaches in which the theories are thought to describe readings of certain measurement operations. The usual axioms are shown to correspond with classes of ideal measurements. The necessity is discussed of generalizing the formalisms of both quantum mechanics and relativity theory so as to encompass more realistic nonideal measurements. It is argued that this generalization favours an empiricist interpretation of the mathematical formalisms over a realist one.

In Situ Multi-Wavelength Ellipsometric Control of Thickness and Composition For Bragg Reflector Structures

AbstractWe have demonstrated real-time feedback control of thickness and composition for Bragg reflector structures using in situ multi-wavelength ellipsometry. This demonstration was performed under conditions which were not ideal for ellipsometric measurements: the angle of incidence for the ellipsometric measurement beam was far away from the Brewster angle, substrate rotation was enabled (which caused an angular wobble in the measurement beam), and strain effects were present in the ellipsometer windows. Furthermore, to simulate drift in the MBE system (and test the effectiveness of the ellipsometer control), the Ga effusion cell was ramped to change the Ga flux by 50% during two of the growth runs. Results of the growth control precision and accuracy are presented; the influence of the non-ideal measurement conditions on the ellipsometer growth control capability is also discussed.

Experimental study of repeatability errors in 3D sound intensity measurements in narrow frequency bands

When investigating the 2D or 3D intensity of complex ‘real life’ noise sources, rather than the intensity normal to a surface, to obtain more detailed information about the radiated sound field great care has to be taken both in measuring and in interpreting the results. In this study it is shown that in measurements of 3D intensity for fixed points and in narrow frequency bands, large errors can be expected for a well-defined simple source if the positioning is imprecise and for a complex source even if the positioning device and the probe are of highest quality. Comparisons have been made between a two-microphone and a six-microphone probe, hand-held and robot-controlled. The comparisons show that, except for the case of an ideal measurement with a simple source and a high-precision robot, significant errors can be expected for all the tested measurement cases. The measurements also show that the positioning of the microphone is of major importance for the repeatability accuracy. The accuracy obtained with a 3D-probe is notably better than with a 1D-probe. The errors when measuring the complex source with a robot-controlled 3D-probe, however, are still so high, especially for the non-dominant directions, that interpretations have to be made with great care. Under non-ideal measurement conditions, the errors are found to be exponentially dependent upon the sound field pressure/intensity relationship (the pI-index).

Information in neutron interference experiments

Wigner measures are calculated for a number of neutron interference experiments that can be interpreted as joint nonideal measurements of path and interference. It is demonstrated that the Wigner measure need not be influenced by fluctuations, thus showing that fluctuations need not diminish the information content of the experiment. A measurement is proposed yielding complete information on the incoming neutron state.

Non-ideal measurements

We have previously objected to modal interpretations of quantum theory by showing that these interpretations do not assign outcomes to non-ideal measurements. Bub and Healey replied (in this journal) by offering alternative accounts of non-ideal measurements. In this paper we argue, first, that our account of non-ideal measurements is correct and, second, even if it is not correct, it is overwhelmingly likely that interactions satisfying our characterization of non-ideal measurements actually occur and that such interactions possess outcomes. A successful defense of the modal interpretation must assign outcomes to these interactions or show that they do not have outcomes or show that in fact they never occur. Bub and Healey show none of this.

Nonlinear regression technique for parameter extraction from field-emission data

The standard method for obtaining field emission parameter estimates from current–voltage data is to transform the Fowler–Nordheim equation [L. W. Nordheim, Proc. R. Soc. London Ser. A 119, 626 (1928)] with approximate elliptical functions such that a linear regression technique can be used to obtain the emission area and enhancement factor estimates for a given work function. We present here a method for obtaining the parameter estimates that avoids bias caused by the functional approximations and the data transformation required for the previous method. The parameter bias due to several nonideal measurement situations is also considered. Finally, the method is applied to experimental data.

The Bell inequalities and the joint measurement of incompatible observables

A quantum-mechanical theory of joint nonideal measurement of incompatible polarization observables is applied to an EPR-like experiment. It is demonstrated that this experiment yields both information satisfying and information violating the Bell inequalities. The measurement is also discussed in the context of a local hidden-variables theory. It is argued that the violation of an additional assumption of reproducibility of the hidden variable rather than violation of locality may be responsible for the violation of the Bell inequalities.