共查询到20条相似文献,搜索用时 15 毫秒
1.
2.
S. Link H.A. Dürr W. Eberhardt 《Applied Physics A: Materials Science & Processing》2000,71(5):525-528
We have investigated the population dynamics of image-potential states on the clean Pt(111) surface. The first two image-potential
states have been resolved exhibiting lifetimes of 26±7 fs and 62±7 fs. Those lifetimes are in contrast to the (111) surfaces
of Ag and Cu, where the n=2 state is degenerate with bulk states leading to lifetimes shorter than 20 fs.
Received: 30 March 2000 / Accepted: 2 September 2000 / Published online: 12 October 2000 相似文献
3.
In a photonic realization of qubits the implementation of quantum logic is rather difficult due to the extremely weak interaction
on the few photon level. On the other hand, in these systems interference is available to process the quantum states. We formalize
the use of interference by the definition of a simple class of operations which include linear-optical elements, auxiliary
states and conditional operations.
We investigate an important subclass of these tools, namely linear-optical elements and auxiliary modes in the vacuum state.
For these tools, we are able to extend a previous qualitative result, a no-go theorem for perfect Bell-state analyzer on two
qubits in polarization entanglement, by a quantitative statement. We show that within this subclass it is not possible to
discriminate unambiguously four equiprobable Bell states with a probability higher than 50%.
Received: 18 July 2000 / Revised version: 15 September 2000 / Published online: 6 December 2000 相似文献
4.
We consider the ground states of the ferromagnetic XXZ chain with spin up boundary conditions. The ground state of this model,
restricted to a sector with a fixed number of down spins, describes a droplet of down spins in an environment of up spins.
We find the exact energy and the states that describe these droplets in the limit of an infinite number of down spins. We
prove that there is a gap in the spectrum above the droplet states. As the XXZ Hamiltonian has a gap above the fully magnetized
ground states as well, this means that the droplet states (for sufficiently large droplets) form an isolated band. The width
of this band tends to zero in the limit of infinitely large droplets. We also prove the analogous results for finite chains
with periodic boundary conditions and for the infinite chain.
Received: 5 September 2000 / Accepted: 8 December 2000 相似文献
5.
M. Weinelt 《Applied Physics A: Materials Science & Processing》2000,71(5):493-502
Quantum-phase and population decay of image-potential states have been investigated by two-photon photoemission with femtosecond
time resolution. The influence of steps and defects on quasielastic and inelastic scattering processes is illustrated for
a vicinal Cu(119) surface and diluted adsorbate layers of CO and Cu on Cu(001).
Received: 19 April 2000 / Accepted: 2 September 2000 / Published online: 12 October 2000 相似文献
6.
We propose a definition of entropy production in the framework of algebraic quantum statistical mechanics. We relate our
definition to heat flows through the system. We also prove that entropy production is non-negative in natural non-equilibrium
steady states.
Received: 7 August 2000 / Accepted: 5 September 2000 相似文献
7.
P. Desgrolard M. Giffon E. Martynov E. Predazzi 《The European Physical Journal C - Particles and Fields》2000,14(4):683-694
An extensive generalization of the ordinary and quasi-eikonal methods is presented for the pp and elastic scattering amplitudes, which takes into account in a phenomenological way all intermediate multiparticle states involving
the crossing even and crossing odd combinations of Reggeons. The formalism in this version involves a maximum of three parameters
corresponding to the intermediate states which are possible in this configuration. The unitarity restriction is investigated
and particular cases are discussed. An interesting result that emerges concerns the Odderon trajectory intercept: we find
that unitarity dictates that this quantity must be below or equal unity unless a very peculiar equality exists between the coupling of the particles to the Pomeron and the
Odderon.
Received: 3 September 1999 / Revised version: 21 February 2000 / Published online: 8 May 2000 2000 相似文献
8.
S. Tarucha D.G. Austing S. Sasaki Y. Tokura W. van der Wiel L.P. Kouwenhoven 《Applied Physics A: Materials Science & Processing》2000,71(4):367-378
The effects of direct Coulomb and exchange interactions on spin states are studied for quantum dots contained in circular
and rectangular mesas. For a circular mesa a spin-triplet favored by these interactions is observed at zero and nonzero magnetic
fields. We tune and measure the relative strengths of these interactions as a function of the number of confined electrons.
We find that electrons tend to have parallel spins when they occupy nearly degenerate single-particle states. We use a magnetic
field to adjust the single-particle state degeneracy, and find that the spin-configurations in an arbitrary magnetic field
are well explained in terms of two-electron singlet and triplet states. For a rectangular mesa we observe no signatures of
the spin-triplet at zero magnetic field. Due to the anisotropy in the lateral confinement single-particle state degeneracy
present in the circular mesa is lifted, and Coulomb interactions become weak. We evaluate the degree of the anisotropy by
measuring the magnetic field dependence of the energy spectrum for the ground and excited states, and find that at zero magnetic
field the spin-singlet is more significantly favored by the lifting of level degeneracy than by the reduction in the Coulomb
interaction. We also find that the spin-triplet is recovered by adjusting the level degeneracy with magnetic field.
Received: 14 April 2000 / Accepted: 17 April 2000 / Published online: 6 September 2000 相似文献
9.
In the setting of vector-valued quantum fields obeying a linear wave-equation in a globally hyperbolic, stationary spacetime,
it is shown that the two-point functions of passive quantum states (mixtures of ground- or KMS-states) fulfill the microlocal
spectrum condition (which in the case of the canonically quantized scalar field is equivalent to saying that the two-pnt function
is of Hadamard form). The fields can be of bosonic or fermionic character. We also give an abstract version of this result
by showing that passive states of a topological *-dynamical system have an asymptotic pair correlation spectrum of a specific
type.
Received: 9 February 2000 / Accepted: 7 June 2000 相似文献
10.
We distinguish six classes of families of locally equivalent states in a straightforward scheme for classifying all 2–q-bit
states; four of the classes consist of two subclasses each. The simple criteria that we stated recently for checking a given
state’s positivity and separability are justified, and we discuss some important properties of Lewenstein–Sanpera decompositions.
An upper bound is conjectured for the sum of the degree of separability of a 2–q-bit state and its concurrence.
Received: 17 July 2000 / Published online: 6 December 2000 相似文献
11.
A. Abele et al. 《The European Physical Journal C - Particles and Fields》2001,19(4):667-675
A simultaneous analysis of two different final states from annihilation at rest is used to study the decays of isoscalar states into . The data demand two scalar states, the with , and the with mass and width compatible with previous findings. Apart from the dominant scalar intensity, the (1300) plays an important role in the 5 dynamics. We find a mass of and a width of with a dominant decay into . The decay of the is less than 15% of its decay.
Received: 13 September 2000 / Revised version: 4 January 2001 / Published online: 6 April 2001 相似文献
12.
Taku Matsui 《Communications in Mathematical Physics》2001,218(2):393-416
We consider the relationship between the symmetry breaking and the split property of pure states of quantum spin chains.
We obtain a representation theoretic condition implying that the half-sided uniform mixing condition leads to symmetry breaking
of translationally invariant pure states. This is a mathematical generalization of Dichotomy previously found by I. Affleck and E. Lieb and M. Aizenman and B. Nachtergaele for ground states of a special class of Hamiltonians.
Received: 1 February 1999 / Accepted: 5 December 2000 相似文献
13.
Shu Nakamura 《Communications in Mathematical Physics》2000,214(3):565-572
We study the behavior of the density states at the lower edge of the spectrum for Schr?dinger operators with random magnetic
fields. We use a new estimate on magnetic Schr?dinger operators, which is similar to the Avron–Herbst–Simon estimate but the
bound is always nonnegative.
Received: 3 January 2000 / Accepted: 18 April 2000 相似文献
14.
J. Clausen H. Hansen L. Knöll J. Mlynek D.-G. Welsch 《Applied physics. B, Lasers and optics》2001,72(1):43-50
The U(1,1) and U(2) transformations realized by three-mode interaction in the respective parametric approximations are studied
in conditional measurement, and the corresponding non-unitary transformation operators are derived. As an application, the
preparation of single-mode quantum states using an optical feedback loop is discussed, with special emphasis on Fock-state
preparation. For that example, the influence of non-perfect detection and feedback is alsoconsidered.
Received: 12 July 2000 / Revised version: 19 September 2000 / Published online: 30 November 2000 相似文献
15.
The phenomena in optical pattern formation are reviewed using a single mirror feedback experiment as an example. The nonlinear
medium is sodium metal vapor. We discuss the mechanism responsible for the spontaneous formation of spatial structures and
the selection between simple periodic patterns as hexagons and squares. Introducing a polarization changing element in the
feedback loop, quasiperiodic patterns with a twelve-fold rotational symmetry are obtained and their properties are studied
by filtering methods in Fourier space. Finally, we discuss the formation of localized states as spatial solitons due to a
self-induced lensing effect. Their interaction is studied and the formation of clusters provides a link between localized
states and extended patterns. Genuine optical features, such as the polarization degrees of freedom, the experimental accessibility
of the Fourier space, and the possibility to control the optical susceptibility of atomic vapors by means of an external magnetic
field, provide very powerful tools for investigating the principles of pattern formation.
Received: 15 July 2000 / Revised version: 7 November 2000 / Published online: 6 December 2000 相似文献
16.
We have observed hysteresis loops in current transport in a GaAs metal–semiconductor–metal diode containing InAs quantum dots.
The dots in our structure are directly embedded under the GaAs–metal interface. The charging and discharging of electrons
in the dots modulate the current and produce hysteresis. These processes are controlled by the applied voltages. The dots
are charged by forward current flowing through the structure. The discharging of the electrons is dominated by the tunneling
process under high reverse bias. The modulated currents are well fitted with an electron-trapping model considering both the
ground states and the excited states of the quantum dots.
Received: 5 October 2000 / Accepted: 12 December 2000 / Published online: 23 May 2001 相似文献
17.
H. Albrecht 《The European Physical Journal C - Particles and Fields》2000,16(3):435-444
A measurement of gamma–gamma production of the final states , , , and was performed by the ARGUS collaboration at the storage ring DORIS II at DESY. Since the two intermediate states and are accessible by analysing different final states, the measurement provides several cross checks for cross-sections to these
two states. The results for cross-sections obtained from different final states are found to be consistent with each other. The analysis of the partial
wave structure of the state from the reaction revealed the dominance of the wave.
Received: 17 December 1999 / Published online: 8 June 2000 相似文献
18.
A. Jokinen J.C. Wang J. Äystö P. Dendooven S. Nummela J. Huikari V. Kolhinen A. Nieminen K. Peräjärvi S. Rinta-Antila 《The European Physical Journal A - Hadrons and Nuclei》2000,9(1):9-12
Beta decay of a refractory isotope 118Rh produced in symmetric fission and mass separated by the ion guide technique has been applied for the study of low-lying
excited states of 118Pd. The yrast band in 118Pd has been observed up to a 6+ state and the lowest states of the asymmetric γ-band have been identified. The measured half-life of 118Rh is (300±60)ms. The systematics of the excited states in neutron-rich Pd-isotopes implies the saturation towards an O(6) symmetry at N = 70.
Received: 19 June 2000 / Accepted: 1 August 2000 相似文献
19.
Sh. Mamedov 《The European Physical Journal C - Particles and Fields》2001,18(3):523-529
The analytical properties of the photon polarization operator in the quark vacuum was analyzed. Branching points of the polarization
operator were found and its imaginary part was calculated. Quantum transitions between quark states and the turning over of
a quark's color spin in a chromomagnetic field were predicted. The negative values of the photon energy and the contribution
of the photon zero energy to the branching point were taken into account
Received: 20 July 2000 / Published online: 21 December 2000 相似文献
20.
Jerome P. Gauntlett Gary W. Gibbons Christopher M. Hull Paul K. Townsend 《Communications in Mathematical Physics》2001,216(2):431-459
We find the combinations of momentum and domain-wall charges corresponding to BPS states preserving 1/4, 1/2 or 3/4 of D=4
N=1 supersymmetry, and we show how the supersymmetry algebra implies their stability. These states form the boundary of the
convex cone associated with the Jordan algebra of 4× 4 real symmetric matrices, and we explore some implications of the associated
geometry. For the Wess–Zumino model we derive the conditions for preservation of 1/4 supersymmetry when one of two parallel
domain-walls is rotated and in addition show that this model does not admit any classical configurations with 3/4 supersymmetry.
Our analysis also provides information about BPS states of N=1 D=4 anti-de Sitter supersymmetry.
Received: 6 April 2000/ Accepted: 10 September 2000 相似文献