On the Sharpness and Bias of Quantum Effects

The question of quantifying the sharpness (or unsharpness) of a quantum mechanical effect is investigated. Apart from sharpness, another property, bias, is found to be relevant for the joint measurability or coexistence of two effects. Measures of bias will be defined and examples given.     

Notes on Joint Measurability of Quantum Observables

For sharp quantum observables the following facts hold: (i) if we have a collection of sharp observables and each pair of them is jointly measurable, then they are jointly measurable all together; (ii) if two sharp observables are jointly measurable, then their joint observable is unique and it gives the greatest lower bound for the effects corresponding to the observables; (iii) if we have two sharp observables and their every possible two outcome partitionings are jointly measurable, then the observables themselves are jointly measurable. We show that, in general, these properties do not hold. Also some possible candidates which would accompany joint measurability and generalize these apparently useful properties are discussed.     

Compatibility and Marginality

We present a way of introducing joint distibution function and its marginal distribution functions for non-compatible observables. Each such marginal distribution function has the property of commutativity. Models based on this approach can be used to better explain some classical phenomena in stochastic processes.     

Quantum World with Quantum Time

Since the beginning of quantum mechanics there have been a lot of attempts to quantize time. In this paper we refer to the little known concept of quantum time proposed by E.Kapuscik [Hadronic J. 8 (1985) 75]. We analyze some properties of systems with quantum time. Moreover we comment and discuss the idea of quantum time.     

A simple bakeable particle detector: Ion-electron converter plus solid state electron detector

We describe a simple particle detector using the principle of the ion-electron converter. It detects ions and neutral particles, has low background noise (0.1 counts/s), and is bakeable at 280°C. The energy resolution of the electron detector is better than 2.0 keV, thus allowing the frequency distribution of the electron groups to be observed directly in the pulse height spectrum. The marked differences between the electron statistics for ions and for metastable neutrals are used in an application to mass-analysis. An improvement in signal to noise ratio by more than a factor of ten is achieved.     

Geometry of the electron local observables

We show that the complete set of the second power identities for the electron local observables consists of 36 equations. The identities connect the products of the electron bilinear forms and, being considered as geometrically meaningful equations in 3D Euclidean space, are separated over the groups of equations for the scalar, vector and tensor quantities. Considering the complete set of identities as a set of the second power equations, we solve the equations and find the irreducible representation for the electron local observables. The representation defines the 16 electron local observables as functions of 7 basic parameters and can be formulated in 6 various forms. The basic parameters include scalar and pseudoscalar, the time components of a 4-vector and a 4-pseudovector, and three Euler angles which define the angular position of a local 3D frame with respect to the 3D laboratory frame. These 7 parameters completely define the space components of the 4-vector and the 4-pseudovector, as well as the polar and axial vectors. The developed representation shows that the analysis of the any electron wave packet can be considerably simplified by the reduction of the number of analyzed real functions from 16 to 7. As an example, we present the structure of the local observables defined by the irreducible representation in a case of a traveling electron wave.     

The symmetry of the Hubbard model

The spectrum of the Hubbard model shows permanent degeneracy of levels with different symmetries, if one considers only symmetry operators independent of the coupling constant. This suggests the existence of symmetry operators which depend on the coupling constant. We find these highly nontrivial operators and show that they explain the degeneracies in the energy spectrum.Part of project No. P5588 of the Fonds zur Förderung der wissenschaftlichen Forschung in Österreich.     

Commutative POVMs and Fuzzy Observables

In this paper we review some properties of fuzzy observables, mainly as realized by commutative positive operator valued measures. In this context we discuss two representation theorems for commutative positive operator valued measures in terms of projection valued measures and describe, in some detail, the general notion of fuzzification. We also make some related observations on joint measurements. This article is dedicated to Pekka Lahti on the occasion of his 60th birthday.     

Recoil polarimetry in meson photoproduction at MAMI

The nucleon excitation spectrum remains poorly known, with the masses, widths, EM couplings and even existence of many states not well established. A program of experiments using meson photoproduction off the nucleon is being carried out to improve this situation. A new large acceptance recoil polarimeter has been developed by the Edinburgh group for use in such reactions with the Crystal Ball at MAMI. This work summarizes the procedure used to measure recoil polarization with the new device and presents some preliminary results for the double polarization observable Cx in the reaction γp→pπ, compared to the current partial wave analysis.     

经典守恒定律的量子力学推导

从量子力学出发,推出了经典动量守恒定律和能量守恒定律,并讨论了在微观领域经典守恒定律适用的条件.     

Recoil polarimetry in meson photoproduction at MAMI

The nucleon excitation spectrum remains poorly known, with the masses, widths, EM couplings and even existence of many states not well established. A program of experiments using meson photoproduction off the nucleon is being carried out to improve this situation. A new large acceptance recoil polarimeter has been developed by the Edinburgh group for use in such reactions with the Crystal Ball at MAMI. This work summarizes the procedure used to measure recoil polarization with the new device and presents some preliminary results for the double polarization observable C_x in the reaction γp→pπ~0, compared to the current partial wave analysis.     

On the Structure of the Observable Algebra for QED on the Lattice

We prove that the matter field subalgebra of the observable algebra for QED on a finite lattice is isomorphic to the enveloping algebra of the Lie algebra sl(2N, C), factorized by a certain ideal. Using this result, we give a new proof of the decomposition of the physical Hilbert space into charge superselection sectors.     

Comparison of FM dye lasers in standing-wave and ring configuration

We have compared the operation of a frequency-modulated dye laser (FML) in a standing-wave and ring configuration. As expected, for a given frequency detuning (difference between the drive frequency for the phase modulator and the cavity mode spacing) the enhanced modulation index is twice as large for the standing-wave configuration as for the ring configuration. In addition, we have demonstrated that application of small amounts of phase modulation in the ring configuration leads to improved mode stability. The fine structure of the rf beats for both FM lasers, have been studied and the results suggest that spatial hole burning complicates the detailed structure.     

New approach for measuring bubble collapse field of LPE garnet layers

A new method based on the superposition of a sinusoidally varying alternating field with increasing amplitude on the constant bias magnetic field normal to the plane of an LPE garnet film is proposed for precise, objective photoelectrical determination of the bubble collapse field. The method avoids subjective errors in the determination of the collapse field, it gives information on hard bubbles, and for serial measurements it can even be implemented without a measuring microscope.     

Influence of fluctuating pulse durations on the time resolution of probing experiments

Fluctuating pulse durations considerably influence the time resolution of probing experiments. The commonly used arithmetic averaging the experimental data changes the shape of the signal curves and gives longer decay times in the wings. Methods are presented to reduce the effect of fluctuating pulse durations.     

Covariant fuzzy observables and coarse-graining

A fuzzy observable is regarded as a smearing of a sharp observable, and the structure of covariant fuzzy observables is studied. It is shown that the covariant coarse-grainings of sharp observables are exactly the covariant fuzzy observables. A necessary and sufficient condition for a covariant fuzzy observable to be informationally equivalent to the corresponding sharp observable is given.     

The use of parallel and monochromatic beams for determining the composition of pseudobinary alloys by X-ray fluorescence

A simple X-ray fluorescence method using nearly parallel and monochromatic beams is analyzed and discussed in connection with the determination of the alloy fraction in pseudobinary A_1−x B _x C solid solutions. Applications to optoelectronic materials are considered. The reliability of the method has been analyzed and discussed for both bulk and thin film samples. Errors due to small angular divergence in the accepted beam are seen to be neglibile. Deviations from a symmetrical alignment of the sample can strongly influence the measured fluorescence intensity. The experimental analysis of this effect can be used for a perfect symmetrical orientation of thick samples. The measurement of the fluorescence intensity as a function of the glancing angle can give both thickness and composition in solid-solution thin-film samples. The contributions of the fluorescence radiation excited by the characteristic X-ray lines of atoms within the substrate is shown to be important in thin epitaxial layers. An approximate formula for calculating these contributions is given and discussed in the light of experimental results. Bulk crystals and thin-film samples, vapourphase grown Cd_1−x Zn _x S solid solutions, have been used for experiments in which the ZnK _α radiation excited by a MoK _α primary beam was measured.     

The analysis of excite and probe measurements of relaxation times with fluctuating pulse duration

The effect of fluctuations in the pulse duration of synchronously pumped modelocked pulse trains on excite and probe measurements is discussed. Relaxation times comparable with the pulse durations can be measured even when large pulse-to-pulse fluctuations in duration exist. The pump and probe pulse durations are assumed to be correlated. When the probe pulses are the second harmonic of the pump, or vice versa, the third harmonic must also be generated to permit deconvolution of experimental excite and probe data. When the pump and probe pulses have the same time dependence, the excite and probe curves consist of the desired response function convolved with the time-averaged second harmonic autocorrelation function which is easily measured. Deconvolution yields the relaxation time but fluctuations in pulse duration increase the root-mean-square voltage fluctuation at the output of the detector system and limit the accuracy with which the relaxation time can be calculated.