Showing papers on "Quantum published in 1968"
TL;DR: In this article, a microscopically correct Hamiltonian with Bose operators of light and Fermi operators of the optically active electrons in the medium is considered and the effect of these heatbaths is taken into account in a quantum mechanically consistent fashion.
Abstract: Our treatment is based on a microscopically correct Hamiltonian which contains the Bose-operators of the light modes and the Fermi-operators of the optically active electrons in the medium. The coupling between modes and atoms is taken from quantum-electrodynamics. Besides that, the light modes may interact with external “heat baths” like the mirrors, scattering centers etc., while the atoms interact with lattice vibrations, incoherent light fields etc. Using recently developed methods the effect of these heatbaths is taken into account in a quantum mechanically consistent fashion. In the present paper we apply quantum mechanical Langevin equations for the field and electron operators which contain dissipation and fluctuation terms. The elimination of the electron operators by an iteration procedure finally leaves us with a set of coupled nonlinear field equations which are shown to be quantum mechanically consistent. They are solved in the Heisenberg picture below threshold by linearization and well above threshold by quantum mechanical quasi-linearization. The solutions show that the line width of the signal mode below threshold is due to the vacuum fluctuations in the idler and vice versa, whereas the thermal noise of the resonator and the spontaneous emission noise of the medium may be neglected. Above threshold the linewidth is caused by the undamped diffusion of the phase difference between signal and idler, to which the vacuum fluctuations of both modes contribute in equal parts. The phase sum of both modes adiabatically follows the slow phase diffusion of the external pump light, produced by a laser, and therefore contributes to the linewidth too. Well above threshold the amplitudes are stable. Correlation and cross-correlation functions of their small residual fluctuations are calculated.
128 citations
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38 citations
25 citations
TL;DR: In this paper, the conditions under which the quantum mechanical diffraction approach attains correspondence with the more familiar classical analysis are discussed by considering only two waves, though a full quantum mechanical discussion requires a multiple beam consideration for the prediction of transmitted intensities.
Abstract: The transmission of fast charged particles through thin crystals may be considered within the framework of either classical or quantum mechanics. The conditions under which the quantum mechanical diffraction approach attains correspondence with the more familiar classical analysis is discussed by considering only two waves, though a full quantum mechanical discussion requires a multiple beam consideration for the prediction of transmitted intensities. With increasing particle mass m for a fixed potential of interaction complementarity may be conveniently visualized in reciprocal space as being achieved when the angular width of the Bragg resonances exceeds the angular separation of the resonances themselves. Inelastic scattering produces a transmission pattern on the exit surface of the crystal of the kind first described by Kikuchi (1928). When correspondence occurs, and this may be determined by comparing the magnitude of a simple dimensionless parameter α with unity, angular widths of lines an...
25 citations
23 citations
TL;DR: In this article, a criterion to distinguish the properties of a plasma as to whether it is classical or quantum mechanical in nature can be defined in terms of three fundamental lengths of the electron gas.
Abstract: The ‘quantum electrodynamics’ of the scattering of radiation from a fully ionized, interacting plasma is to be considered.The plasma particle interaction must properly be treated quantum mechanically when the electron plasma wave phonon energies are comparable to or greater than the mean random electron energies and/or when the phonon momenta are of the order of magnitude or greater than the average electron momenta in the plasma.In these two circumstances or either one of them, the plasma particle inter action must be treated in a quantum mechanical manner. The ‘solid-state’ plasma recently discussed by D.E.McCumber is an example of a quantum plasma.Whether a classical or a quantum plasma is considered, the collective properties, as well as the single-particle properties, need to be considered. The collective properties of the plasma become important when it interacts with a radiation field in the case where the electron plasma frequency, ωp, is of the same order of magnitude, or exceeds, the operating radiation frequency ω, i.e. ωp≥ω.A criterion to distinguish the properties of a plasma as to whether it is classical or quantum mechanical in nature can be defined in terms of three fundamental lengths of the electron gas. These definitions hold for a one-component plasma. They are: the classical length βe2, the Debye screening length and the thermal de Broglie wavelength defined as 1/kT. From these three quantities, we can define two dimensionless parameters. They are the classical parameter and the quantum parameter δ=λ/λD which is a measure of the quantum effects. For a quantum plasma δ>1 and in the classical limit (h = 0),δ=0, Λ<1.When we take into account the collective behaviour characterized by the plasma oscillations, screening effects are an automatic aspect of the electron plasma gas.It is hoped that the present review article will provide the background material for general understanding of the field and easy access to the current literature. It is also hoped that the present discussion will establish greater interest in this subject.As an example of a calculation of plasma properties, a calculation of the generalized dielectric constant for both a low-density plasma in the classical limit and a high-density plasma in the quantum mechanical limit is performed and compared in a suitable manner.
21 citations
TL;DR: The interpretation of the experimental results is in accordance with the hypothesis that one single quantum of light is sufficient to trigger an elementary photochemical reaction and that in turn one single photochemical event can elicit a miniature receptor potential.
Abstract: Light quanta impinging upon the photopigments located in the rhabdomeric receptor structures of the fly's compound eyes trigger photochemical reactions which in turn elicit miniature receptor potentials (bumps). The paper mainly deals with the problem whether a single quantum of light is sufficient, or whether a coincidence of quanta and/or elementary photochemical events is necessary to trigger a miniature receptor potential. The experiments were based on tests of the optomotor responses of fixed flying flies suspended in a rotating patterned cylinder with periodic distributions of inner surface brightness. The tests were made under two different light programs: 1) Illumination constant in time 2) Illumination by periodic light pulse sequences with various frequencies. Average light fluxes absorbed by the receptors were equal in both programs. Theoretical considerations lead to the following conclusions: The strength of the optomotor responses to the light programs 1 and 2 should not differ from each other in the case of single quantum processes. However for multiquantum processes light program 2 should be more effective than light program 1 as it favours the coincidence of quantum absorptions per unit time. But these theoretical conclusions are valid only if two conditions are fulfilled in the experiments: a) The pulse frequency of light program 2 has to be kept below a certain limit which is determined by the kinetics of the photochemical systems. Otherwise light program 2 gets averaged in time and in principle can be not more effective than light program 1. b) The rates of quanta absorbed by the receptors have to be kept low enough to guarantee that the concentration of unbleached pigment molecules remains practically unchanged as compared with the concentration in darkness. Accordingly the test experiments were carried out with light pulse frequencies ranging from 500 to 1/120 cycles per second. Intensities were used which corresponded to an average quantum flux effective for one rhabdomeric structure ranging between 10 and 250 quanta per second. The interpretation of the experimental results is in accordance with the hypothesis that one single quantum of light is sufficient to trigger an elementary photochemical reaction and that in turn one single photochemical event can elicit a miniature receptor potential. At present time the experiments do not allow conclusions about the possible occurrence of coincidence-functions of synapses at the level of the first optical ganglion which receive their information via fibers leading off from the receptors. In one of the appendices of the paper, the transinformation flux into a receptor is calculated, taking into consideration the Poisson noise of the quanta disrupting the signal at extremely low quantum rates.
20 citations
TL;DR: In this paper, general theorems relating to the ordering of functions of operators are presented, and integral representations for them are given for applications to phase space descriptions of quantum mechanical systems.
17 citations
TL;DR: Using a Jastrow basis, variation method, and a cluster expansion approximation, this paper computed the cohesive energy and P-V relation for solid molecular hydrogen and developed a pair function having physical and computational utility over a wider range of density than those previously employed in quantum crystals.
TL;DR: In this paper, quantum corrections to the pair distribution function of a plasma at high temperature and low density are calculated to order e 2 in the interaction, using standard diagram perturbation techniques.
Abstract: Quantum‐mechanical corrections to the pair distribution function of a plasma at high temperature and low density are calculated to order e2 in the interaction, using standard diagram perturbation techniques. Both the effects due to quantum statistics (exchange) and the finite size of a wave packet (dynamic screening), are considered.
TL;DR: In this paper, the growth rate of synchrotron radiation at wave normal angle θ = 90° was derived by means of the classical kinetic approach, and it was shown that the result is identical with that obtained from the quantum treatment.
Abstract: In a system of isotropic relativistic electrons which is embedded in a cold ambient magnetoactive plasma, the growth rate of synchrotron radiation at wave normal angle θ = 90° is derived by means of the classical kinetic approach. It is shown that the result is identical with that obtained from the quantum treatment. Two errors occurring in the literature of synchrotron radiation are pointed out. The growth rate is computed for the case of monoenergetic electrons as an example.
TL;DR: In this paper, the authors considered a sample of randomly oriented molecules in arigid medium excited with unpolarized light and showed that the probability of finding an excited absorption oscillator at a given value of (Y is proportional to sin3&.
Abstract: IN MOST determinations of luminescence quantum yield, the luminescence is observed in a certain direction and the observed intensity is compared with that from a standard sample, on the assumption that the same fraction of the total intensity is measured. In general, however, different spatial intensity distributions will be obtained from different luminescent samples. Although this is a well known fact, that has been discussed in connection with quantum yield measurement [ 11, it is usually overlooked. A calculation of the maximum error that may be introduced by this neglect is therefore of interest. Some methods of avoiding this type of error will be mentioned. Finally, errors caused by the ‘eigenpolarization’ of the apparatus will be briefly discussed. Consider a sample of randomly oriented molecules in arigid medium excited with unpolarized light. The directions of excitation and observation are at right angles, defining the yand z-axes of the coordinate system in Fig 1. In a molecule the linear absorption and emission oscillators, ha and me, are at an angle 6 to one another. The directions of the oscillators in the coordinate system are specified by the angles a, p and 8, 4. The probability of finding an excited absorption oscillator at a given a value of (Y is proportional to sin3&. The contribution to the observed intensity from one emission oscillator is proportional to sin2& The observed intensity may be taken as a weighted mean of the contributions from all emission oscillators, the weights being given by the excitation probabilities:
Journal Article•
TL;DR: In this article, the authors examined pump power losses associated with electron backscattering and pair creation and showed that power retention and ionization yield reflect target characteristics (atomic number and bandgap energy) only.
Abstract: The object is to identify and assess factors and mechanisms that control the conversion of electron-beam power into coherent light through excitation of a semiconductor laser cavity. First, we examine the question of pump power losses associated with electron backscattering and pair creation. It is shown that power retention and ionization yield reflect target characteristics (atomic number and bandgap energy) only. The external quantum efficiency, which is best expressed as a product of quantum yield, coherence ratio, and escape probability, involves two parameters: pumping ratio and output coupling. This leads to a straightforward optimization procedure. Heating effects are analyzed in terms of a differential quantum efficiency and are shown to degrade the saturation value of the efficiency by a factor roughly proportional to the pulse rise time, if adiabatic conditions hold. These considerations are illustrated using power-efficiency figures reported for CdS, CdTe, and GaAs lasers; it is demonstrated that the photon-loss coefficient of excited "perfect" CdS must be less than 1.5 cm-1, at 4.2°K.
01 Jan 1968
TL;DR: In this paper, the authors directly observed quantum phase fluctuations at the onset of long-range quantum phase coherence in single-crystal bulk tin as it becomes superconducting.
Abstract: We have directly observed quantum phase fluctuations at the onset of long-range quantum phase coherence in single-crystal bulk tin as it becomes superconducting.
TL;DR: Methods of spectrally characterizing radiant energy are intercompared and a new terminology for a volt per quantum, a planck, is proposed.
Abstract: Methods of spectrally characterizing radiant energy are intercompared. For quantum devices the advantages of spectral characterizations in terms of quanta per second and energy per quanta are presented. These are expanded into the concepts of optical currents and voltages. A new terminology for a volt per quantum, a planck, is proposed.
TL;DR: It is demonstrated that analog models of static as well as dynamic inhibition in the retina can be extended to more realistic stochastic models by consideration of the coincidence operations as expressed in the quantum coincidence and quantum fluctuation models for visual threshold behavior.
Abstract: Well-known theoretical concepts for visual threshold behavior are: 1. the quantum coincidence model which describes particularly threshold-dependence on presentation time and teststimulus geometry; 2. the quantum fluctuation model which includes description of thresholddependence on luminance and color of a masking background. In this paper it is demonstrated that analog models of static as well as dynamic inhibition in the retina can be extended to more realistic stochastic models. This can be done by consideration of the coincidence operations as expressed in the quantum coincidence and quantum fluctuation models for visual threshold behavior. In this model coincidence detectors indicated as C-gates are the essential components. It is demonstrated that threshold-gates as are frequently used in models in neurophysiology do not permit development of the more realistic asynchronous circuits. Further it is pointed out that electronic neuron models and stochastic and nonstochastic models of nerve-functions of other authors in fact are either special simplifications of the proposed C-gates or lead naturally to C-gates for their further development.
TL;DR: Representation for real functions of quantum mechanical momentum operator obtained by functional integration in phase space is given.
Abstract: Representation for real functions of quantum mechanical momentum operator obtained by functional integration in phase space
TL;DR: In this article, the double-hump detuning phenomenon of two-cavity molecular beam masers is explained quantum-mechanically, and the detuning process is shown to be reversible.
TL;DR: A review of the current state of the historiography of quantum physics can be found in this article, where a survey of the secondary literature, divided as to general treatises (Section I), biographies and autobiographies (Section II), and monographs (Section III), is presented.
Abstract: THE following is an account of the current state of the historiography of quantum physics, by which I understand the theory and application of the quantum from its discovery in 1900 to the early thirties, when most of the problems connected with it had found their modern solutions. The review begins with a survey of the secondary literature, divided as to general treatises (Section I), biographies and autobiographies (Section II), and monographs (Section III). It proceeds to describe the Archive for History of Quantum Physics (Section IV) and to suggest some problems which might profitably be studied with the help of the documentation the Archive offers (Section V). It concludes (Section VI) with a few general remarks on advantages an historian may derive from studying the recent development of the science in whose history he specialises. The development of quantum physics was intimately linked to that of other branches of physical science, particularly statistical mechanics, the study of radioactivity, spectral analysis, and the theory of atomic structure. So, of course, was it connected somehow with the general cultural and social milieu in which it grew. One could increase the references given here tenfold by including items which, though apparently tangential to the main topic, will be found very relevant to the study of certain aspects of it. To reduce the compass of the review, I have generally excluded from it writings not pertaining directly to quantum theory, to the theory of atomic structure, or to the more speculative study of radioactivity and spectral regularities. Nor have I included later philosophical discussions of the Copenhagen interpretation, though literature pertaining to its development and acceptance is noticed. Also I have ignored, with very few exceptions, the brief retrospective articles and highly abbreviated histories one finds in, say, Nat-ure, the Journal of chemical education. and Physikalische Blatter. This review is therefore a very selective one. Within the categories admitted, however, I have tried to give a complete account of recent and current literature. No doubt there are omissions. I am much obliged, as usual, to my friend Professor Paul Forman of the University of Rochester for filling some gaps and for suggesting several improvements.
TL;DR: In this paper, the authors reported the observation of both fast and slow quantum oscillations of large amplitude in the magnetoresistance of tin and successfully simulated them by a quantum mechanical resistance calculation for a chain of coupled circular free-electron orbits under the condition that phase-coherence is important on all links of the chain.
Abstract: This paper reports the observation of both fast and slow quantum oscillations of large amplitude in the magnetoresistance of tin. The observations are successfully simulated by a quantum mechanical resistance calculation for a chain of coupled circular free-electron orbits under the condition that phase-coherence is important on all links of the chain. This paper reports the observation of both fast and slow quantum oscillations of large amplitude in the magnetoresistance of tin. The observations are successfully simulated by a quantum mechanical resistance calculation for a chain of coupled circular free-electron orbits under the condition that phase-coherence is important on all links of the chain.