共查询到20条相似文献,搜索用时 10 毫秒
1.
We study the effect of quantum and classical phase fluctuations on the phase transitions in the system of Josephson-junction arrays. We employed a variational method for calculating the Gaussian type fluctuation of the phase in the Josephson-junction array lattice systems without and with an external magnetic field. We investigate the spectrum of collective excitations and the effects of collective excitations on the transport properties of Josephson-junction arrays. We showed that the Hamiltonian for the lattice system of the Josephson junction is the same as the Hamiltonian for the classical or quantum two-dimensional interacting rotators. We also showed that the dynamics of fluctuations of the phase in the lattice system of Josephson junction is very similar to the lattice dynamics of the lattice in crystals. We also showed that in the lattice system of Josephson junctions there is the collective acoustic mode similar to the acoustic mode in the crystal lattice, and this mode may lead to the dissipation of the Josephson current in the superconducting array of Josephson junctions. The speed of sound of the collective acoustic mode of the phase fluctuation depends on the Josephson coupling energy and the Coulomb charging energy. The contribution of the collective acoustic mode to the low temperature specific heat is the same as the contribution of the acoustic phonons to the specific heat of crystals. We also discuss the future development of results and their application. 相似文献
2.
Anatoli Serghei Jodie L. Lutkenhaus Daniel F. Miranda Kathleen McEnnis Friedrich Kremer Thomas P. Russell 《Small (Weinheim an der Bergstrasse, Germany)》2010,6(16):1822-1826
Phase transitions of polymeric materials are accompanied by changes in density as a function of temperature. Being able to measure these changes in polymeric systems in one, two or three dimensions on the nanoscopic length‐scale is a challenge, but it would provide a simple route to assess phase transitions in nanoscopically confined systems. It is shown that the measurement of the dielectric permittivity in the high frequency limit (in spectral regions not affected by dielectric dispersions) offers an effective and very sensitive means to assess density fluctuations, and hence phase transitions, in nanoscopic systems. The sensitivity of this approach is demonstrated by assessing the phase transition behavior of ferroelectric polymer nanowires confined within alumina membranes. No significant shifts in the Curie transition are observed down to pore diameters as small as 15 nm. 相似文献
3.
Based on an attractive U Hubbard model on a lattice with up to second neighbor hopping we derive an effective Hamiltonian for phase fluctuations. The superconducting gap is assumed to have s-wave symmetry. The effective Hamiltonian we finally arrive at is of the extended XY type. While it correctly reduces to a simple XY in the continuum limit, in the general case, it contains higher neighbor interaction in spin space. An important feature of our Hamiltonian is that it gives a much larger fluctuation region between the Berezinskii–Kosterlitz–Thouless transition temperature identified with T c for superconducting and the mean field transition temperature identified with the pseudogap temperature. 相似文献
4.
Ömer Çakiroglu 《Journal of Superconductivity and Novel Magnetism》2000,13(4):639-644
The influence of the quantum fluctuations of the order parameter's phase on the critical temperature T c is studied for a Josephson coupled layered superconductor. Two characteristic critical temperatures exist for a system, namely the superconducting critical temperature T (2) c for a single layer estimated by the mean-field theory and the transition temperature for the outset or the superconducting phase coherence T* c . The true critical temperature T c is shown to vary inside the intervals T* c ≤ T c ≤ T (2) c . For a strong quantum phase fluctuation limit, the superconducting layers become decoupled. 相似文献
5.
Ömer Çakiroglu 《Journal of Superconductivity》2000,13(4):639-644
The influence of the quantum fluctuations of the order parameter's phase on the critical temperature T
c
is studied for a Josephson coupled layered superconductor. Two characteristic critical temperatures exist for a system, namely the superconducting critical temperature T
(2)
c
for a single layer estimated by the mean-field theory and the transition temperature for the outset or the superconducting phase coherence T*
c
. The true critical temperature T
c
is shown to vary inside the intervals T*
c
T
c
T
(2)
c
. For a strong quantum phase fluctuation limit, the superconducting layers become decoupled. 相似文献
6.
Hai-Woong Lee 《Journal of Modern Optics》2013,60(6):1081-1089
Abstract Quadrature variances of a radiation field depend not only on the photon number distribution in the field but also on the relative phases of the photon number probability amplitudes. Two fields with the same photon number distribution can show different degrees of squeezing if photon number states are superposed with different relative phases. It is thus possible, for example, for a radiation field with Poissonian photon statistics to exhibit squeezed quadrature fluctuations. Since different relative superposition phases in general yield different maximum and minimum values of the quadrature variances, measurement of the variances can yield information concerning the relative phases between different number states. 相似文献
7.
《Journal of Modern Optics》2013,60(9-10):1023-1037
The occurrence of photon antibunching and squeezing is strongly connected with nonlinear optical phenomena in general. Recent results are presented for two-atom resonance fluorescence, the anharmonic oscillator, nonlinear propagation of light and higher-harmonic generation. 相似文献
8.
Abstract The interactions among radiation modes in optical fibres and other Kerr media can create correlations among two, four or more distinct field components. These correlations can reduce the noise levels found with various detector schemes. Some interactions produce the correlations required for quantum non-demolition detection. 相似文献
9.
本文对特种激光外差通信系统接收中频信号相位受大气湍流随机起伏进行了实验测试。实验结果表明:该系统有助于克服大气湍流对接受中频信号相位的随机起伏,由大气湍流带来的随机相位噪声可以不予考虑。 相似文献
10.
Abstract It is shown that some 17 Rydberg Na atoms initially placed into a coherent atomic state and super-radiating into a low-Q microwave cavity at temperatures T ? 0·4 K will show modest squeezing in the fluorescence field, the squeezing arising from terms oscillating at twice the cavity frequency. It is also shown that similar numbers of Rydberg atoms undergoing resonance fluorescence in a coherent single-mode microwave driving field and without any cavity will show more substantial squeezing in the fluorescence field. 相似文献
11.
Paulina Marian 《Journal of Modern Optics》2013,60(3):285-293
Abstract The conditions for obtaining squeezing by single-beam multiphoton absorption are examined. For an initial coherent light the amount of squeezing is calculated in the second order of interaction time using the master-equation formalism. A limit formula for the amount of squeezing is found in the case of an initial strong coherent beam. The results are compared with the exact numerical calculations and some remarks are made on the short-time approximation in multiphoton absorption. 相似文献
12.
Abstract The production of squeezed states in second-harmonic generation is discussed theoretically from the viewpoint of the structure of the nonlinear medium, phase-matching conditions, and the polarization state of the fields. The nonlinear coupling constants are derived in explicit form for all 102 magnetic symmetry groups for crystalline as well as electrically polarized isotropic media. The phase-matching conditions are discussed in detail. Phase mismatch is shown to accumulate along the optical path, and is calculated in full detail for various media and geometries. We refer to this as the mismatch accumulation effect. General formulae for normally ordered variances of the second-harmonic and fundamental fields are derived by perturbative procedure, and are specified for some special cases of practical interest. 相似文献
13.
D.J. Scalapino 《Journal of Low Temperature Physics》1999,117(3-4):179-188
The organizers of the Memorial Session for Herman Rietschel asked that I review some of the history of the interplay of superconductivity and spin fluctuations. Initially, Berk and Schrieffer showed how paramagnon spin fluctuations could suppress superconductivity in nearly-ferromagnetic materials. Following this, Rietschel and various co-workers wrote a number of papers in which they investigated the role of spin fluctuations in reducing the T
c
of various electron-phonon superconductors. Paramagnon spin fluctuations are also believed to provide the p-wave pairing mechanism responsible for the superfluid phases of
3
He. More recently, antiferromagnetic spin fluctuations have been proposed as the mechanism for d-wave pairing in the heavy-fermion superconductors and in some organic materials as well as possibly the high-T
c
cuprates. Here I will review some of this early history and discuss some of the things we have learned more recently from numerical simulations. 相似文献
14.
15.
16.
《Journal of Modern Optics》2013,60(8):945-948
A comparison is made between exact numerical results of the squeezing parameters in single-mode two-photon absorption with those predicted by short-time calculations. Numerical calculations lead to much higher squeezing and at longer times than those predicted by short-time calculations. The value of the squeezing parameter in the limit of long times and large initial photon numbers coincides in both calculations, as well as in the limit of long times and small initial photon numbers. 相似文献
17.
Abstract A unique approach to the photon statistics in nonlinear optical interactions is suggested based on the use of moment equations and generalized superposition of coherent fields and quantum noise. Non-classical features such as squeezing of fluctuations and sub-Poisson statistics are derived for finite interaction times in the three-mode interaction process and limits of the model are provided. 相似文献
18.
Abstract We discuss the connection between quantum correlations and squeezing in simple quantum optical systems. We illustrate this connection by a study of two-mode states of light produced by parametric down-conversion and similar two-photon processes. The intermode correlations in these systems are shown to be responsible for modifications in photon-number sum and difference operators, and for squeezing in the superpositions of the two modes. The disappearance of the diagonal coherent-state quasiprobability function P(α) when non-classical light properties are important is noted, and alternative and better-behaved Wigner functions and coherent-state expectation Q-functions for the two-mode system are developed. 相似文献
19.
Photographic emulsions are found to have experimentally-measured detective quantum efficiencies with peak values of less than 3%. Although such low values have been demonstrated to be not far removed from the highest values attainable with high-latitude on/off detectors of the silver halide type, they have nevertheless given rise to widely conflicting opinions concerning the influence on photographic granularity of the photon fluctuations in the exposure. This is essentially due to the complexity of the photographic process, which obscures the statistical processes which are inherent to the input/output relationship of the photon/grain interaction.General arguments are developed which indicate the inevitability of a causal relationship between photon noise and granularity. Calculations are made of the quantitative contribution to detector noise from the photon fluctuations for a hypothetical detector having intrinsic properties which approximate to those of practical photographic emulsions. 相似文献