共查询到20条相似文献,搜索用时 31 毫秒
1.
M. Manninen M. Koskinen S.M. Reimann B. Mottelson 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):381-385
Exact many-body methods as well as current-spin-density functional theory are used to study the magnetism and electron localization
in two-dimensional quantum dots and quasi-one-dimensional quantum rings. Predictions of broken-symmetry solutions within the
density functional model are confirmed by exact configuration interaction (CI) calculations: In a quantum ring the electrons
localize to form an antiferromagnetic chain which can be described with a simple model Hamiltonian. In a quantum dot the magnetic
field localizes the electrons as predicted with the density functional approach.
Received 5 December 2000 相似文献
2.
Electronic structure of three-dimensional quantum dots 总被引:1,自引:0,他引:1
T. Vorrath R. Blümel 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(2):227-235
We study the electronic structure of three-dimensional quantum dots using the Hartree-Fock approximation. The confining potential
of the electrons in the quantum dot is assumed to be spatially isotropic and harmonic. For up to 40 interacting electrons
the ground-state energies and ground-state wavefunctions are calculated at various interaction strengths. The quadrupole moments
and electron densities in the quantum dot are computed. Hund's rule is confirmed and a shell structure is identified via the addition energies and the quadrupole moments. While most of the shell structure can be understood on the basis of the
unperturbed non-interacting problem, the interplay of an avoided crossing and the Coulomb interaction results in an unexpected
closed shell for 19 electrons.
Received 5 November 2001 / Received in final form 12 November 2002 Published online 1st April 2003
RID="a"
ID="a"e-mail: vorrath@physnet.uni-hamburg.de 相似文献
3.
S.A. Mikhailov K. Ziegler 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(1):117-120
A floating Wigner crystal differs from the standard one by a spatial averaging over positions of the Wigner-crystal lattice.
It has the same internal structure as the fixed crystal, but contrary to it, takes into account rotational and/or translational
symmetry of the underlying jellium background. We study properties of a floating Wigner molecule in few-electron spin-polarized
quantum dots, and show that the floating solid has the lower energy than the standard Wigner crystal with fixed lattice points.
We also argue that internal rotational symmetry of individual dots can be broken in arrays of quantum dots, due to degenerate
ground states and inter-dot Coulomb coupling.
Received 12 September 2001 / Received in final form 24 April 2002 Published online 9 July 2002 相似文献
4.
J.M. Cerveró A. Rodrıguez 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(2):239-251
We present the exact diagonalization of the Schr?dinger operator corresponding to a periodic potential with N deltas of different couplings, for arbitrary N. This basic structure can repeat itself an infinite number of times. Calculations of band structure can be performed with
a high degree of accuracy for an infinite chain and of the correspondent eigenlevels in the case of a random chain. The main
physical motivation is to modelate quantum wire band structure and the calculation of the associated density of states. These
quantities show the fundamental properties we expect for periodic structures although for low energy the band gaps follow
unpredictable patterns. In the case of random chains we find Anderson localization; we analize also the role of the eigenstates
in the localization patterns and find clear signals of fractality in the conductance. In spite of the simplicity of the model
many of the salient features expected in a quantum wire are well reproduced.
Received 24 June 2002 Published online 29 November 2002 相似文献
5.
Ben-Yuan Gu Yao Lu Tzong-Jer Yang 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(4):493-502
We present numerical investigations of the transmission properties of electrons in a normal quantum wire tangentially attached
to a superconductor ring threaded by magnetic flux. A point scatterer with a δ -function potential is placed at node to model
scattering effect. We find that the transmission characteristics of electrons in this structure strongly depend on the normal
or superconducting state of the ring. The transmission probability as a function of the energy of incident electrons, in the
case of a superconductor ring threaded by one quantum magnetic flux, emerges one deep dip, imposed upon the first broad bump
in spectrum. This intrinsic conductance dip originates from the superconductor state of the ring. When increasing the magnetic
flux from one quantum magnetic flux to two, the spectrum shifts toward higher energy region in the whole. This conductance
dip accordingly shifts and appears in the second bump. In the presence of a point-scatterer at the node, the spectrum is substantially
modified. Based on the condition of the formation of the standing wave functions in the ring and the broken of the time-reserve
symmetry of Schr?dinger equation after switching magnetic flux, the characteristics of transmission of electrons in this structure
can be well understood.
Received 6 November 2001 相似文献
6.
7.
M. Terraneo B. Georgeot D.L. Shepelyansky 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,22(1):127-130
We show that dissipative classical dynamics converging to a strange attractor can be simulated on a quantum computer. Such
quantum computations allow to investigate efficiently the small scale structure of strange attractors, yielding new information
inaccessible to classical computers. This opens new possibilities for quantum simulations of various dissipative processes
in nature.
Received 10 August 2002 Published online 29 October 2002
RID="a"
ID="a"e-mail: dima@irsamc.ups-tlse.fr
RID="b"
ID="b"UMR 5626 du CNRS 相似文献
8.
Z.Á. Németh J.-L. Pichard 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(1):87-101
In this second paper, using N = 3 polarized electrons (spinless fermions) interacting via a U/r Coulomb repulsion on a two dimensional L×L square lattice with periodic boundary conditions and nearest neighbor hopping t, we show that a single unpaired fermion can co-exist with a correlated two particle Wigner molecule for intermediate values
of the Coulomb energy to kinetic energy ratio r
s = UL/(2t
). This supports in an ultimate mesoscopic limit a possibility proposed by Andreev and Lifshitz for the thermodynamic limit:
a quantum crystal may have delocalized defects without melting, the number of sites of the crystalline array being smaller
than the total number of particles. When L = 6, the ground state exhibits four regimes as rs increases: a Hartree-Fock regime, a first supersolid regime where a correlated pair co-exists with a third fully delocalized
particle, a second supersolid regime where the third particle is partly delocalized, and eventually a correlated lattice regime.
Received 22 October 2002 Published online 23 May 2003
RID="a"
ID="a"e-mail: jpichard@cea.fr 相似文献
9.
U. Yurtsever D. Strekalov J.P. Dowling 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,22(3):365-371
A quantum gravity-gradiometer consists of two spatially separated ensembles of atoms interrogated by pulses of a common laser
beam. The laser pulses cause the probability amplitudes of atomic ground-state hyperfine levels to interfere, producing two,
motion-sensitive, phase shifts, which allow the measurement of the average acceleration of each ensemble, and, via simple
differencing, of the acceleration gradient. Here we propose entangling the quantum states of atoms from the two ensembles
prior to the pulse sequence, and show that entanglement encodes their relative acceleration in a single interference phase
which can be measured directly, with no need for differencing.
Received 6 June 2002 / Received in final form 25 October 2002 Published online 28 January 2003 相似文献
10.
I.O. Kulik T. Hakioğlu A. Barone 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(2):219-226
We examine a generic three level mechanism of quantum computation in which all fundamental single and double qubit quantum
logic gates are operating under the effect of adiabatically controllable static (radiation free) bias couplings between the
states. Under the time evolution imposed by these bias couplings the quantum state cycles between the two degenerate levels
in the ground state and the quantum gates are realized by changing Hamiltonian at certain time intervals when the system collapses
to a two state subspace. We propose a physical implementation of the mechanism using Aharonov-Bohm persistent-current loops
in crossed electric and magnetic fields, with the output of the loop read out by using a quantum Hall effect aided mechanism.
Received 26 March 2002 / Received in final form 8 July 2002
Published online 19 November 2002 相似文献
11.
Y. Li Voskoboynikov C.P. Lee S.M. Sze O. Tretyak 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(4):475-481
In this article we study the impact of the spin-orbit interaction on the electron quantum confinement for narrow gap semiconductor
quantum dots. The model formulation includes: (1) the effective one-band Hamiltonian approximation; (2) the position- and
energy-dependent quasi-particle effective mass approximation; (3) the finite hard wall confinement potential; and (4) the
spin-dependent Ben Daniel-Duke boundary conditions. The Hartree-Fock approximation is also utilized for evaluating the characteristics
of a two-electron quantum dot system. In our calculation, we describe the spin-orbit interaction which comes from both the
spin-dependent boundary conditions and the Rashba term (for two-electron quantum dot system). It can significantly modify
the electron energy spectrum for InAs semiconductor quantum dots built in the GaAs matrix. The energy state spin-splitting
is strongly dependent on the dot size and reaches an experimentally measurable magnitude for relatively small dots. In addition,
we have found the Coulomb interaction and the spin-splitting are suppressed in quantum dots with small height.
Received 15 May 2001 / Received in final form 14 May 2002 Published online 13 August 2002 相似文献
12.
M. Specht M. Sanquer S. Deleonibus G. Guégan 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(4):503-508
We report observation of the Kondo effect in the Coulomb blockade oscillations of an impurity quantum dot (IQD). This IQD
is formed in the channel of a 100 nm gate length Silicon MOSFET. The quantitative analysis of the anomalous temperature and
voltage dependence for the drain-source current over a series of Coulomb blockade oscillations is performed. It strongly supports
the Kondo explanation for the conductance behavior at very low temperature in this standard microelectronics device.
Received 13 November 2001 and Received in final form 18 February 2002 相似文献
13.
Pil H. Song ILki Kim 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(2):299-303
We study the effects of dissipation or leakage on the time evolution of Grover's algorithm for a quantum computer. We introduce
an effective two-level model with dissipation and randomness (imperfections), which is based upon the idea that ideal Grover's
algorithm operates in a 2-dimensional Hilbert space. The simulation results of this model and Grover's algorithm with imperfections
are compared, and it is found that they are in good agreement for appropriately tuned parameters. It turns out that the main
features of Grover's algorithm with imperfections can be understood in terms of two basic mechanisms, namely, a diffusion
of probability density into the full Hilbert space and a stochastic rotation within the original 2-dimensional Hilbert space.
Received 12 August 2002 / Received in final form 14 October 2002 Published online 4 February 2003 相似文献
14.
Quantum spin dynamics as a model for quantum computer operation 总被引:1,自引:0,他引:1
H. De Raedt K. Michielsen A. Hams S. Miyashita K. Saito 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(1):15-28
We study effects of the physical realization of quantum computers on their logical operation. Through simulation of physical
models of quantum computer hardware, we analyze the difficulties that are encountered in programming physical realizations
of quantum computers. Examples of logically identical implementations of the controlled-NOT operation and Grover's database
search algorithm are used to demonstrate that the results of a quantum computation are unstable with respect to the physical
realization of the quantum computer. We discuss the origin of these instabilities and discuss possibilities to overcome this,
for practical purposes, fundamental limitation of quantum computers.
Received 5 November 2001 and Received in final form 8 February 2002 相似文献
15.
G. Benenti G. Casati S. Montangero D.L. Shepelyansky 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(2):293-296
We study the properties of eigenstates of an operating quantum computer which simulates the dynamical evolution in the regime
of quantum chaos. Even if the quantum algorithm is polynomial in number of qubits nq, it is shown that the ideal eigenstates become mixed and strongly modified by static imperfections above a certain threshold
which drops exponentially with nq. Above this threshold the quantum eigenstate entropy grows linearly with nq but the computation remains reliable during a time scale which is polynomial in the imperfection strength and in nq.
Received 7 March 2002/ Received in final form 3 May 2002 Published online 19 July 2002 相似文献
16.
J. Gemmer G. Mahler 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(2):249-257
For a closed bi-partite quantum system partitioned into system proper and environment we interpret the microcanonical and
the canonical condition as constraints for the interaction between those two subsystems. In both cases the possible pure-state
trajectories are confined to certain regions in Hilbert space. We show that in a properly defined thermodynamical limit almost
all states within those accessible regions represent states of some maximum local entropy. For the microcanonical condition
this dominant state still depends on the initial state; for the canonical condition it coincides with that defined by Jaynes'
principle. It is these states which thermodynamical systems should generically evolve into.
Received 13 June 2002 / Received in final form 14 November 2002 Published online 4 February 2003
RID="a"
ID="a"e-mail: jochen@theol.physik.uni-stuttgart.de 相似文献
17.
K. Maschke T. Meier P. Thomas S.W. Koch 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(4):599-606
The coherent dynamics of magnetoexcitons in semiconductor nanorings following pulsed optical excitation is studied. The calculated
temporal evolution of the excitonic dipole moment may be understood as a superposition of the relative motion of electrons
and holes and a global circular motion associated with the magnetic-field splitting of these states. This dynamics of the
electron-hole pairs can be generated either by local optical excitation of an ordered ring or, alternatively, by homogeneous
excitation of rings with broken rotational symmetry due to disorder or band tilting.
Received 27 September 2000 相似文献
18.
M. Genovese C. Novero 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,21(1):109-113
We propose a quantum transmission based on bi-photons, which are doubly-entangled both in polarisation and phase. This scheme
finds a natural application in quantum cryptography, where we show that an eventual eavesdropper is bound to introduce a larger
error on the quantum communication than for a single entangled bi-photon communication, when he steels the same information.
Received 23 July 2001 / Received in final form 30 November 2001 Published online 24 September 2002 相似文献
19.
G. Benenti G. Casati S. Montangero D.L. Shepelyansky 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,22(2):285-293
We investigate the transition to quantum chaos, induced by static imperfections, for an operating quantum computer that simulates
efficiently a dynamical quantum system, the sawtooth map. For the different dynamical regimes of the map, we discuss the quantum
chaos border induced by static imperfections by analyzing the statistical properties of the quantum computer eigenvalues.
For small imperfection strengths the level spacing statistics is close to the case of quasi-integrable systems while above
the border it is described by the random matrix theory. We have found that the border drops exponentially with the number
of qubits, both in the ergodic and quasi-integrable dynamical regimes of the map characterized by a complex phase space structure.
On the contrary, the regime with integrable map dynamics remains more stable against static imperfections since in this case
the border drops only algebraically with the number of qubits.
Received 19 June 2002 / Received in final form 30 September 2002 Published online 17 Decembre 2002
RID="a"
ID="a"e-mail: dima@irsamc.ups-tlse.fr
RID="b"
ID="b"UMR 5626 du CNRS 相似文献
20.
C.P. Sun X.F. Liu D.L. Zhou S.X. Yu 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,17(1):85-92
To account for the phenomenon of quantum decoherence of a macroscopic object, such as the localization and disappearance of
interference, we invoke the adiabatic quantum entanglement between its collective states (such as that of the center-of-mass
(CM)) and its inner states based on our recent investigation. Under the adiabatic limit where motion of the CM does not excite
the transition of inner states, it is shown that the wave function of the macroscopic object can be written as an entangled
state with correlation between adiabatic inner states and quasi-classical motion configurations of the CM. Since the adiabatic
inner states are factorized with respect to each component of the macroscopic object, this adiabatic separation can induce
the quantum decoherence. This observation thus provides us with a possible solution to the Schr?dinger cat paradox.
Received 24 October 2000 and Received in final form 8 March 2001 相似文献