共查询到20条相似文献,搜索用时 15 毫秒
1.
This paper considers the most general linear transformation of a quantum state. We enumerate the conditions necessary to retain a physical interpretation of the transformed state: hermiticity, normalization and complete positivity. We show that these can be formulated in terms of an associated transformation introduced by Choi in 1975. We extend his treatment and display the mathematical argumentation in a manner closer to that used in traditional quantum physics. We contend that our approach displays the implications of the physical requirements in a simple and intuitive way. In addition, defining an arbitrary vector, we may derive a probability distribution over the spectrum of the associated transformation. This fixes the average of the eigenvalue independently of the vector chosen. The formal results are illustrated by a couple of examples. 相似文献
2.
Shuji Tsubaki Naoki Fujita Fujio Wakaya Yoshihiko Yuba Kenji Gamo 《Superlattices and Microstructures》2000,27(5-6)
Series of double quantum dots each with a size around 400 × 400nm2 have been realized by delineating a 2DEG in modulation-doped AlGaAs/GaAs with 100 nm wide Schottky split gates fabricated by an electron-beam lithography and a lift-off technique. The split gate in the middle of the double dot allows us to control interdot coupling widely. The charging diagram obtained from linear transports in the Coulomb blockade regime shows that the isolated dots merge into a single composite dot with increase of interdot coupling. A clear Coulomb staircase has been observed in the double-dot system at a limited high-bias condition. 相似文献
3.
We characterize equilibrium states of quantum systems by a condition of passivity suggested by the second principle of thermodynamics. Ground states and -KMS states for all inverse temperatures 0 are completely passive. We prove that these states are the only completely passive ones. For the special case of states describing pure phases, assuming the passivity we reproduce the results of Haag et al. 相似文献
4.
Shimon Malin 《Foundations of Physics》1986,16(12):1297-1305
In a previous article it was shown that in general quantum states represent perspectives on the potentialities of quantum systems, rather than the potentialities themselves. In the present paper the following questions are investigated in the context of this result: (1) How do quantum states which undergo collapse transform under pure translations? (2) Under what conditions do quantum states represent the potentialities themselves? Two alternatives are presented in response to the first question: (1) Quantum states are scalars under translations. (2) The collapse of a quantum state propagates between frames of reference at the speed of light. The advantages and disadvantages of the two alternatives are discussed. The response to the second question is shown to depend on the chosen alternative. In addition, the second alternative is shown to lead to a consistent view of quantum states as “potential perspectives on potentialities.” 相似文献
5.
6.
Ola Bratteli Akitaka Kishimoto Derek W. Robinson 《Communications in Mathematical Physics》1978,64(1):41-48
We prove that ground states of quantum spin systems are characterized by a principle of minimum local energy and that translationally invariant ground states are characterized by the principle of minimum energy per unit volume. 相似文献
7.
Geoffrey L. Sewell 《Communications in Mathematical Physics》1977,55(1):63-66
We extend the characterisation of metastability, as given in [1] for classical systems, to show that quantal lattice systems with suitable long range forces can support metastable states. 相似文献
8.
In this article we review the experimental and theoretical investigations of the linear and nonlinear optical properties of semiconductor quantum well structures, including the effects of electrostatic fields, extrinsic carriers and real or virtual photocarriers. 相似文献
9.
In this paper we study the quantum phase properties of “nonlinear coherent states” and “solvable quantum systems with discrete spectra” using the Pegg-Barnett formalism in a unified approach. The presented procedure will then be applied to few special solvable quantum systems with known discrete spectrum as well as to some new classes of nonlinear oscillators with particular nonlinearity functions. Finally the associated phase distributions and their nonclasscial properties such as the squeezing in number and phase operators have been investigated, numerically. 相似文献
10.
Pregnell KL 《Physical review letters》2006,96(6):060501
Using only linear interactions and a local parity measurement we show how entanglement can be detected between two harmonic oscillators. The scheme generalizes to measure both linear and nonlinear functionals of an arbitrary oscillator state. This leads to many applications including purity tests, eigenvalue estimation, entropy, and distance measures--all without the need for nonlinear interactions or complete state reconstruction. Remarkably, experimental realization of the proposed scheme is already within the reach of current technology with linear optics. 相似文献
11.
We show by using the mean-field approximation that the states of composite Fermi-Bose superfluids created in cold-atom traps via a Feshbach resonance at zero temperature are generalized SU(2)⊗SU(1,1) coherent states. In response to a sudden change of the interaction between fermionic atoms and bosonic molecules, a Cooper pair can exhibit collapse and revival quantum behaviors for an initial generalized coherent state of molecules, and Rabi oscillation for a vacuum molecular state. Occurrence of the collapse and revival phenomenon is thus the manifestation of the formation of the Bose-Einstein condensate. 相似文献
12.
L. Mayrhofer M. Grifoni 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,56(2):107-125
We present a low energy-theory for non-linear transport in finite-size
interacting single-wall carbon nanotubes. It is based on a microscopic
model for the interacting pz electrons and successive bosonization.
We consider weak coupling to the leads and derive equations of motion
for the reduced density matrix. We focus on the case of large-diameter nanotubes where exchange effects can be neglected.
In this situation the energy spectrum is highly degenerate. Due to the multiple degeneracy, diagonal as well as off-diagonal
(coherences)
elements of the density matrix contribute to the nonlinear transport.
At low bias, a four-electron periodicity with a characteristic ratio
between adjacent peaks is predicted. Our results are in quantitative
agreement with recent experiments. 相似文献
13.
14.
Consensus in directed networks of multiple agents, as an important topic, has become an active research subject. Over the past several years, some types of consensus problems have been studied. In this paper, we propose a novel type of consensus, the generalized consensus (GC), which includes the traditional consensus, the anti-consensus, and the cluster consensus as its special cases. Based on the Lyapunov's direct method and the graph theory, a simple control algorithm is designed to achieve the generalized consensus in a network of agents. Numerical simulations of linear and nonlinear GC are used to verify the effectiveness of the theoretical analysis. 相似文献
15.
J. Heldstab H. Thomas T. Geisel G. Radons 《Zeitschrift für Physik B Condensed Matter》1983,50(2):141-150
We carry out a linear response theory for discrete dynanmical systems with periodic attractors. The symmetry properties of the susceptibility matrix are studied and its eigenvalues and eigenvectors are determined. Close to a period-doubling bifurcation where the susceptibility diverges, its half-width is related to the Lyapunov exponent. At the transition to chaos the susceptibility has some universal behaviour which is described by a critical exponent κ=1?(ln2/lnδ)=0.550193... At the bifurcation points where linear response theory becomes insufficient we also determine the nonlinear response. 相似文献
16.
Translated from Transactions of the Lebedev Physics Institute, Moscow, Vol. 192, pp. 204–220 (1988). 相似文献
17.
In recent years, an approach to discrete quantum phase spaces which comprehends all the main quasiprobability distributions
known has been developed. It is the research that started with the pioneering work of Galetti and Piza, where the idea of
operator bases constructed of discrete Fourier transforms of unitary displacement operators was first introduced. Subsequently,
the discrete coherent states were introduced, and finally, the s-parametrized distributions, that include the Wigner, Husimi, and Glauber–Sudarshan distribution functions as particular cases.
In the present work, we adapt its formulation to encompass some additional discrete symmetries, achieving an elegant yet physically
sound formalism. 相似文献
18.
For spin-lattice systems, the Kubo formula, expressing the relaxation function in terms of the linear response function, is found to be exact in the thermodynamic limit. In addition, analyticity properties are obtained. 相似文献
19.
We study the dynamical scattering in one-dimensional systems with a nonlinear side-coupled defect. Such structures exhibit the nonlinear Fano resonances, where nothing can propagate through. We developed a numerical model to study dynamical scattering. According to our analysis the scattering waves become dynamically unstable in the vicinity of the nonlinear Fano resonances, due to modulational instability caused by the presence of nonlinearity. It results in a time-growing amplitude of the nonlinear defect. We also demonstrate the existence of the nonlinear quasi-localized state, supported by such structures. 相似文献
20.
In this work, we study the loss and recovery of pure states (i.e., coherence) in two-state molecules and quantum dots. The molecules of two electronic states and a one-dimensional nuclear vibration are modeled by a quantum–classical dynamical model. According to the simulations, pure states of a two-state molecule can be restored by the excitation of the nuclear vibration by a well-defined electromagnetic field. In the case of a quantum dot, pure states can be regained through the modulation of the energy levels through the application of a proper bias voltage on the dot. 相似文献