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1.
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
2.
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
3.
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
4.
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
5.
Shangwu Ding C.A. McDowell Chaohui Ye Mingsheng Zhan Xiwen Zhu Kelin Gao Xianping Sun Xi-An Mao Maili Liu 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(1):23-35
Magic-angle spinning (MAS) solid state nuclear magnetic resonance (NMR) spectroscopy is shown to be a promising technique
for implementing quantum computing. The theory underlying the principles of quantum computing with nuclear spin systems undergoing
MAS is formulated in the framework of formalized quantum Floquet theory. The procedures for realizing state labeling, state
transformation and coherence selection in Floquet space are given. It suggests that by this method, the largest number of
qubits can easily surpass that achievable with other techniques. Unlike other modalities proposed for quantum computing, this
method enables one to adjust the dimension of the working state space, meaning the number of qubits can be readily varied.
The universality of quantum computing in Floquet space with solid state NMR is discussed and a demonstrative experimental
implementation of Grover's search is given.
Received 19 April 2001 相似文献
6.
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
7.
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
8.
H. Aschauer H.J. Briegel 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(2):171-177
We give a proof that entanglement purification, even with noisy apparatus, is sufficient to disentangle an eavesdropper (Eve)
from the communication channel. Our proof applies to all possible attacks (individual and coherent). Due to the quantum nature
of the entanglement purification protocol, it is also possible to use the obtained quantum channel for secure transmission
of quantum information.
Received 10 August 2001 and Received in final form 26 October 2001 相似文献
9.
Hong-yi Fan J. Chen 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(3):437-442
Based on the newly constructed Einstein, Podolsky and Rosen (EPR) entangled state representation we introduce macroscopic
classical functions associated with atomic coherent state τ with angular momentum value j. These functions are proportional to the ordinary one-variable Hermite polynomials of order 2j. The corresponding Wigner quasiprobability function for τ in phase space is also derived which turns out to be a two-variable Hermite polynomial H
2j, 2j. In so doing, a new classical-quantum correspondence scheme for angular momentum system is established.
Received 7 August 2002 / Received in final form 14 December 2002 Published online 24 April 2003
RID="a"
ID="a"Work supported by the National Natural Science Foundation of China under grant 10175057.
RID="b"
ID="b"e-mail: fhym@sjtu.edu.en 相似文献
10.
11.
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
12.
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
13.
G.-L. Ingold A. Wobst Ch. Aulbach P. Hänggi 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(2):175-179
In the one-dimensional Anderson model the eigenstates are localized for arbitrarily small amounts of disorder. In contrast,
the Aubry-André model with its quasiperiodic potential shows a transition from extended to localized states. The difference
between the two models becomes particularly apparent in phase space where Heisenberg's uncertainty relation imposes a finite
resolution. Our analysis points to the relevance of the coupling between momentum eigenstates at weak potential strength for
the delocalization of a quantum particle.
Received 3 May 2002 / Received in final form 2 October 2002 Published online 29 November 2002 相似文献
14.
W.L. Barnes G. Björk J.M. Gérard P. Jonsson J.A.E. Wasey P.T. Worthing V. Zwiller 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(2):197-210
We examine the problem of efficiently collecting the photons produced by solid-state single photon sources. The extent of
the problem is first established with the aid of simple physical concepts. Several approaches to improving the collection
efficiency are then examined and are broadly categorized into two types. First are those based on cavity quantum dynamics,
in which the pathways by which the source may emit a photon are restricted, thus channeling emission into one desired mode.
Second are those where we try to reshape the free space modes into a target mode in an optimal way, by means of refraction,
without fundamentally altering the way in which the source emits. Respectively, we examine a variety of microcavities and
solid immersion lenses. Whilst we find that the micropillar microcavities offer the highest collection efficiency (∼70%),
choosing this approach may not always be appropriate due to other constraints. Details of the different approaches, their
merits and drawbacks are discussed in detail.
Received 19 July 2001 and Received in final form 5 October 2001 相似文献
15.
P. Navez 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(2):219-228
We describe a cryptographic protocol consisting of two entangled beams of squeezed light which makes use of statistical tests
to deduce the secret key bit. The sender (Alice) encrypts a secret key by modulating the phase of the beam sent in public
by the receiver (Bob) who keeps the other beam private. The knowledge of the degree of non classical correlation between the
beam quadrature components measured in private and in public allows only Bob to decrypt the secret key. With a view towards
absolute security, we formally prove that any external intervention from an eavesdropper (Eve) during the communication process
introduces necessarily some modification susceptible to be detected. Statistical confidentiality tests are proposed to detect
the presence of Eve.
Received 12 July 2001 and Received in final form 11 November 2001 相似文献
16.
A. Wobst G.-L. Ingold P. Hänggi D. Weinmann 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(1):11-14
We introduce phase space concepts to describe quantum states in a disordered system. The merits of an inverse participation
ratio defined on the basis of the Husimi function are demonstrated by a numerical study of the Anderson model in one, two,
and three dimensions. Contrary to the inverse participation ratios in real and momentum space, the corresponding phase space
quantity allows for a distinction between the ballistic, diffusive, and localized regimes on a unique footing and provides
valuable insight into the structure of the eigenstates.
Received 5 March 2002 相似文献
17.
P. Koskinen M. Koskinen M. Manninen 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(4):483-489
Recently it was demonstrated that the rotational and vibrational spectra of quantum rings containing few electrons can be
described quantitatively by an effective spin-Hamiltonian combined with rigid center-of-mass rotation and internal vibrations
of localized electrons. We use this model Hamiltonian to study the quantum rings at finite temperatures and in presence of
a nonzero magnetic field. Total spin, angular momentum and pair correlation show similar phase diagram which can be understood
with help of the rotational spectrum of the ring.
Received 18 January 2002 Published online 13 August 2002 相似文献
18.
R.H. Hernández A. Pacheco 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(2):265-274
We report both two-dimensional numerical simulations and experimental results that confirm the robustness of a new method
for inhibiting vortex shedding associated to the Bénard-von Kármán (BvK) instability in the wake of a cylinder. Using the
SIMPLER algorithm on a 2D channel, we solve the Navier-Stokes equations and we show that pressure suction at the front stagnation
point of a circular cylinder, modelled here through a point sink located at the front stagnation point, can completely suppress
the Bénard-von Kármán instability for super-critical Reynolds numbers. Comparison with recent experimental results are in
close agreement.
Received 7 March 2002 / Received in final form 12 September 2002 Published online 29 November 2002 相似文献
19.
A. Sacchetti 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,21(2):229-232
Here we consider the dynamics of a two-level system under an external time-dependent field. We show that in the case of a
bichromatic field the dynamical localization effect is strongly sensitive with respect to the commensurability of the driving
frequencies.
Received 8 May 2002 / Received in final form 4 July 2002 Published online 24 September 2002
RID="a"
ID="a"e-mail: Sacchetti@unimo.it 相似文献
20.
W. Nörenberg G. Papp P. Rozmej 《The European Physical Journal A - Hadrons and Nuclei》2002,14(1):43-51
Results on dissipative isoscalar modes of a hot and dilute nuclear droplet are presented. As compared to the adiabatic limit
(part I), realistic dissipation yields a substantial reduction of the growth rates for all unstable modes, while the area
of spinodal instability in the (ϱ,T)-plane remains unchanged. The qualitative features of multifragmentation through spinodal decomposition as obtained in the
adiabatic limit are not significantly affected by dissipation.
Received: 10 January 2002 / Accepted: 10 February 2002 相似文献