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1.
研究了无限深势阱内两个粒子的耦合导致的量子退相干和量子行为趋近于经典混沌运动的过程.当一个粒子的质量减小时,它对另外一个粒子经典混沌扩散的影响逐渐减小.强混沌机理使得轻粒子的作用类似于噪声,从而有效得抑制另外一个粒子的量子相干性.轻粒子的退相干效应随着有效普朗克常数的减小逐渐增强.在这个过程中,另外一个粒子的量子扩散从动力学局域化行为逐渐过渡到经典极限.当有效普朗克常数足够小时。它的量子扩散与经典混沌扩散相符合.该粒子的线性墒随时间演化迅速趋近于饱和值,并且饱和值随着有效普朗克常数减小以指数函数形式从零趋近于l. 相似文献
2.
In this paper, we revisit the problem of tracking a single fluorescent molecule in a laser-scanning confocal microscope. We utilize optimal control theory to design a feedback controller and use numerical simulation to analyze its ability to track a molecule in two dimensions. A major theme in this paper is the inclusion of all relevant experimental limitations including moderate signal-to-noise fluorescence detection and the finite-bandwidth response of an electromechanical translation stage. The results presented here demonstrate the experimental feasibility of tracking single fluorescent molecules with diffusion coefficients as large as 0.1 m2/ms. We show that for molecules that are even moderately confined along a third dimension (as, for example, by microscope cover slides), the two-dimensional tracking algorithm appears to be robust and effective. We expect this technology to enable single-molecule experiments with long observation times and high time-resolution. PACS 87.64.Tt; 87.64.Ni; 87.15.Vv 相似文献
3.
The form of the nonrigid bender has changes that here we do render. We add, nicely paired, a term to J2 and regroup factors that are singular. As a result, the nonrigid bender Hamiltonian can now be set up using only Van Vleck perturbation theory, for any triatomic molecule (linear, quasi-linear, or bent). It can be used to calculate the rotation-vibration energies of the molecule to high from the bending potential energy function and the stretch and stretch-bend force constants. 相似文献
4.
Asam Rajesh Malay Bandyopadhyay Arun M. Jayannavar 《The European Physical Journal B - Condensed Matter and Complex Systems》2017,90(12):253
In this work, we consider two different techniques based on reservoir engineering process and quantum Zeno control method to analyze the decoherence control mechanism of a charged magneto-oscillator in contact with different type of environment. Our analysis reveals that both the control mechanisms are very much sensitive on the details of different environmental spectrum (J?(ω)), and also on different system and reservoir parameters, e.g., external magnetic field (r c ), confinement length (r 0), temperature (T), cut-off frequency of reservoir spectrum (ω cut ), and measurement interval (τ). We also demonstrate the manipulation scheme of the continuous passage from decay suppression to decay acceleration by tuning the above mentioned system or reservoir parameters, e.g., r c , r 0, T and τ. 相似文献
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6.
Gyula Bene 《Central European Journal of Physics》2003,1(2):332-343
An “almost diagonal” reduced density matrix (in coordinate representation) is usually a result of environment induced decherence
and is considered the sign of classical behavior. We show that the proton of a ground state hydrogen atom can indeed possess
such a density matrix. This example demonstrates that the “almost diagonal” structure may be derived from an interaction with
a low number of degrees of freedom which play the role of the environment. We also show that decoherence effects in our example
can only be observed if the interaction with the measuring device is significantly faster than the interaction with the environment
(the electron). In the opposite case, when the interaction with the environment is significant during the measurement process,
coherence is maintained. Finally, we propose a neutron scattering experiment on cold He atoms to observe decoherence which
shows up as an additional positive contribution to the differential scattering cross section. This contribution is inversely
proportional to the bombarding energy. 相似文献
7.
Debabrata Goswami 《Pramana》2002,59(2):235-242
We show how the use of optimally shaped pulses to guide the time evolution of a system (‘coherent control’) can be an effective
approach towards quantum computation logic. We demonstrate this with selective control of decoherence for a multilevel system
with a simple linearly chirped pulse. We use a multiphoton density-matrix approach to explore the effects of ultrafast shaped
pulses for two-level systems that do not have a single photon resonance, and show that many multiphoton results are surprisingly
similar to the single-photon results. Finally, we choose two specific chirped pulses: one that always generates inversion
and the other that always generates self-induced transparency to demonstrate an ensemble CNOT gate. 相似文献
8.
V. Kagalovsky A. L. Chudnovskiy 《Journal of Experimental and Theoretical Physics》2013,116(4):657-662
Scattering by magnetic impurities is known to destroy coherence of electron motion in metals and semiconductors. We investigate the decoherence introduced in a single act of electron scattering by a magnetic impurity in a quantum Hall system. For this, we introduce a fictitious nonunitary scattering matrix for electrons that reproduces the exactly calculated scattering probabilities. The strength of decoherence is identified by the deviation of eigenvalues of the product from unity. Using the fictitious scattering matrix, we estimate the width of the metallic region at the quantum Hall effect inter-plateau transition and its dependence on the exchange coupling strength and the degree of polarization of magnetic impurities. 相似文献
9.
We study the decoherence process of an exact solvable model that consists of a central spin-1/2 coupling to the surrounding anisotropy spin-1/2 chain in transverse fields. The Loschrnidt echo is calculated to study the character of decoherence with different degree of anisotropy. Our results show that the degree of anisotropy γ greatly affects the decoherence process of the central spin-system when the spin chain is in weak transverse fields, but it gives weak effect in the strong transverse field. The decoherence process of the central system changed dramatically along the line of the critical points, and this may be explained as the reflection of quantum phase transitions. 相似文献
10.
Values of the dissociation energies and the interaction constants in the long-range potential for the B 3ΠOu+ states of Br2 and Cl2 have been obtained from least-squares fits to the attractive part of the Rydberg-Klein-Rees potentials. The term in r -6 is not negligible even at large internuclear distances corresponding to the last few vibrational levels. The validity of the long-range inverse-power expansion in the internuclear distance r has been investigated. The expansion is valid outside the electron-overlap region given by in agreement with the result found in the analysis of I2. 相似文献
11.
《Comptes Rendus Physique》2012,13(5):454-469
We consider a cavity optomechanical cooling configuration consisting of a mechanical resonator (denoted as resonator b) and an electromagnetic resonator (denoted as resonator a), which are coupled in such a way that the effective resonance frequency of resonator a depends linearly on the displacement of resonator b. We study whether back-reaction effects in such a configuration can be efficiently employed for suppression of decoherence. To that end, we consider the case where the mechanical resonator is prepared in a superposition of two coherent states and evaluate the rate of decoherence. We find that no significant suppression of decoherence is achievable when resonator a is assumed to have a linear response. On the other hand, when resonator a exhibits Kerr nonlinearity and/or nonlinear damping the decoherence rate can be made much smaller than the equilibrium value provided that the parameters that characterize these nonlinearities can be tuned close to some specified optimum values. 相似文献
12.
Volker Bach Walter de Siqueira Pedra Marco Merkli Israel Michael Sigal 《Journal of statistical physics》2014,155(6):1271-1298
We consider a finite-dimensional quantum system coupled to a thermal reservoir and subject to a time-periodic, energy conserving forcing. We show that, if a certain dynamical decoupling condition is fulfilled, then the periodic forcing counteracts the decoherence induced by the reservoir: for small system–reservoir coupling $\lambda $ and small forcing period $T$ , the system dynamics is approximated by an energy conserving and non-dissipative dynamics, which preserves coherences. For times up to order $(\lambda T)^{-1}$ , the difference between the true and approximated dynamics is of size $\lambda +T$ . Our approach is rigorous and combines Floquet and spectral deformation theory. We illustrate our results on the spin-fermion model and recover previously known, heuristically obtained results. 相似文献
13.
M. Ban 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,49(1):147-155
Decoherence of nonclassical properties is studied for a photon system interacting with a transient environment which changes
from a linear attenuator to amplifier during the time evolution. The sufficient condition for quadrature squeezing, sub-Poissonian
photon statistics and entanglement to be completely destructed during the time-evolution is derived. The results are compared
with those obtained for another model of the transient linear amplifier. Furthermore the decoherence caused by a environment
which switches a linear amplifier to attenuator is also investigated. 相似文献
14.
Tridiagonalization of a matrix is equivalent to projection onto a linear chain. In the case of a totally random matrix, this chain has constant nearest-neighbor bonds. A calculation of the projected density-of-states yields Wigner's famous result, that a totally random matrix has a semicircular density-of-states. 相似文献
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16.
This study presents the controller design and tests of a new piezodriven two degree-of freedom (DOF) monolithic stage for precision motion. The computer-controlled system is developed, designed and employed for better displacement error compensation by proportional-integral-derivative (PID) controller based on Internal Model Control (IMC), Iterative Learning Control (ILC) and Disturbance Observer (DO). Experimental results show that stage positioning is precisely controlled (error ≈ 1.42%) for tracking sinusoidal waveforms by IMC and P-type ILC with repeatable disturbance. With additional DO, experiment tests perform error ≈ 0.5% with non-repeatable disturbance up to 16% of the maximum traveling length in roughly 5 iterations. This is close to the hardware reproducibility level. Experimental results show the piezo-stage controlled system can be potentially used for nano technology applications for precision engineering in industrial systems. 相似文献
17.
We study the decoherence of a quantum computer in an environment which is inherently correlated in time and space. We first derive the nonunitary time evolution of the computer and environment in the presence of a stabilizer error correction code, providing a general way to quantify decoherence for a quantum computer. The general theory is then applied to the spin-boson model. Our results demonstrate that effects of long-range correlations can be systematically reduced by small changes in the error correction codes. 相似文献
18.
We discuss a fundamental limitation for the coherent operation of superconducting quantum bits originating from phonon radiation generated in the Josephson junctions of the device. The time dependent superconducting phase across the junction produces an electric field that couples to the underlying crystal lattice via the piezoelectric effect. We determine the radiation resistance of the junction due to phonon emission and derive substantial decoherence rates for the quantum bits, which are compatible with quality factors measured in recent experiments. 相似文献
19.
Vinay Ambegaokar 《Journal of statistical physics》2006,125(5-6):1183-1192
The time development of the reduced density matrix for a quantum oscillator damped by coupling it to an ohmic environment
is calculated via an identity of the Debye-Waller form. Results obtained some years ago by Hakim and the author in the free-particle
limit(10) are thus recovered. The evolution of a free particle in a prepared initial state is examined, and a previously published
exchange(5,9) is illuminated with figures showing no decoherence without dissipation.
PACS number: 03.75.Ss 相似文献
20.
A closed loop learning control concept is introduced for teaching lasers to manipulate quantum systems for the purpose of optimally identifying Hamiltonian information. The closed loop optimal identification algorithm operates by revealing the distribution of Hamiltonians consistent with the data. The control laser is guided to perform additional experiments, based on minimizing the dispersion of the distribution. Operation of such an apparatus is simulated for two model finite dimensional quantum systems. 相似文献