共查询到20条相似文献,搜索用时 31 毫秒
1.
Wu Y Kim ED Xu X Cheng J Steel DG Bracker AS Gammon D Economou SE Sham LJ 《Physical review letters》2007,99(9):097402
Coherent transient excitation of the spin ground states in singly charged quantum dots creates optically coupled and decoupled states of the electron spin. We demonstrate selective excitation from the spin ground states to the trion state through phase sensitive control of the spin coherence via these three states, leading to partial rotations of the spin vector. This progress lays the ground work for achieving complete ultrafast spin rotations. 相似文献
2.
3.
Taku Matsui 《Journal of statistical physics》1990,59(3-4):781-798
We study ground states of quantum Potts models. We construct ground states of certaind-dimensional quantum models as Gibbs measures of ad-dimensional classical spin system. Our results imply that various phenomena of classical spin systems can also be found in quantum ground states. 相似文献
4.
Dutt MV Cheng J Li B Xu X Li X Berman PR Steel DG Bracker AS Gammon D Economou SE Liu RB Sham LJ 《Physical review letters》2005,94(22):227403
We report on the coherent optical excitation of electron spin polarization in the ground state of charged GaAs quantum dots via an intermediate charged exciton (trion) state. Coherent optical fields are used for the creation and detection of the Raman spin coherence between the spin ground states of the charged quantum dot. The measured spin decoherence time, which is likely limited by the nature of the spin ensemble, approaches 10 ns at zero field. We also show that the Raman spin coherence in the quantum beats is caused not only by the usual stimulated Raman interaction but also by simultaneous spontaneous radiative decay of either excited trion state to a coherent combination of the two spin states. 相似文献
5.
We established a large class of exactly soluble spin liquids and chiral spin liquids on three-dimensional helix lattices by introducing Kitaev-type's spin coupling. In the chiral spin liquids, exact stable ground states with spontaneous breaking of the time reversal symmetry are found. The fractionalized loop excitations in both the spin and chiral spin liquids obey non-Abelian statistics. We characterize this kind of statistics by non-Abelian Berry phase and quantum algebra relation. The topological correlation of loops is independent of local order parameter and it measures the intrinsic global quantum entanglement of degenerate ground states. 相似文献
6.
Henley CL 《Physical review letters》2006,96(4):047201
The (three-dimensional) pyrochlore lattice antiferromagnet with Heisenberg spins of large spin length S is a highly frustrated model with a macroscopic degeneracy of classical ground states. The zero-point energy of (harmonic-order) spin-wave fluctuations distinguishes a subset of these states. I derive an approximate but illuminating effective Hamiltonian, acting within the subspace of Ising spin configurations representing the collinear ground states. It consists of products of Ising spins around loops, i.e., has the form of a Z2 lattice gauge theory. The remaining ground-state entropy is still infinite but not extensive, being O(L) for system size O(L3). All these ground states have unit cells bigger than those considered previously. 相似文献
7.
A.K. Hartmann 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(4):619-626
Large numbers of ground states of two-dimensional Ising spin glasses with periodic boundary conditions in both directions
are calculated for sizes up to 402. A combination of a genetic algorithm and Cluster-Exact Approximation is used. For each quenched realization of the bonds
up to 40 independent ground states are obtained. For the infinite system a ground-state energy of e
=-1.4015(3) is extrapolated. The ground-state landscape is investigated using a finite-size scaling analysis of the distribution of overlaps.
The mean-field picture assuming a complex landscape describes the situation better than the droplet-scaling model, where for
the infinite system mainly two ground states exist. Strong evidence is found that the ground states are not organized in an
ultrametric fashion in contrast to previous results for three-dimensional spin glasses.
Received 12 October 1998 相似文献
8.
We report measurements of spin transitions for GaAs quantum dots in the Coulomb blockade regime and compare ground and excited state transport spectroscopy to direct measurements of the spin polarization of emitted current. Transport spectroscopy reveals both spin-increasing and spin-decreasing transitions, as well as higher-spin ground states, and allows g factors to be measured down to a single electron. The spin of emitted current in the Coulomb blockade regime, measured using spin-sensitive electron focusing, is found to be polarized along the direction of the applied magnetic field regardless of the ground state spin transition. 相似文献
9.
I. V. Kukushkin K. von Klitzing K. Eberl 《Physica E: Low-dimensional Systems and Nanostructures》1998,1(1-4)
The spin configuration of the ground state of a two-dimensional electron system is investigated for different FQHE states from an analysis of circular polarization of time-resolved luminescence. The method clearly distinguishes between fully spin polarized, partially spin polarized and spin unpolarized FQHE ground states. We demonstrate that FQHE states which are spin unpolarized or partially polarized at low magnetic fields become fully spin polarized at high fields. Temperature dependence of the spin polarization reveals a nonmonotonic behavior at
. At
and
the electron system is found to be fully spin polarized. This result does not indicate the existence of any skyrmionic excitations in high magnetic field limit. However, at
the observed spin depolarization of electron system at
and
becomes broader for lower magnetic fields, so that full spin polarization remains only in a small vicinity of
. Such a behavior could be considered as a precursor of skirmionic depolarization, which would dominate for smaller ratios between Zeeman and Coulomb energies.We demonstrate that the spin polarization of 2D-electron system at
and
can be strongly affected by hyperfine interaction between electrons and optically spin-oriented nuclears. This result is due to the fact that hyperfine interaction can both enhance and suppress effective Zeeman splitting in fixed external magnetic field. 相似文献
10.
M. Babamoradi M. Heidari Saani A. Ranjbar M. A. Vesaghi Y. Kawazoe 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2011,65(3):597-603
Many-body wavefunctions were utilized to calculate von Neumann’s entropy as an
entanglement measurement for neutral and negatively charged nitrogen vacancy (NV) centers
in diamond. A generalized Hubbard Hamiltonian which considers e-e interaction terms
completely was used to calculate many-electron wavefunctions of the ground and excited
states. Correlation between entanglement and spin density distributed on neighboring atoms
of NV is presented. The behavior of spin density and entanglement under relaxations of
neighboring atoms is the same for all investigated ground and excited states. The results
suggest that the spin density may be used to quantify the entanglemnt and vice versa. 相似文献
11.
We investigate the phase diagram of antiferromagnetic spin ladders with additional exchange interactions on diagonal bonds by variational and numerical methods. These generalized spin ladders interpolate smoothly between the [Formula: see text] chain with competing nn and nnn interactions, the [Formula: see text] chain with alternating exchange and the antiferromagnetic (AF) S = 1 chain. The Majumdar - Ghosh ground states are formulated as matrix product states and are shown to exhibit the same type of hidden order as the AF S = 1 chain. Generalized matrix product states are used for a variational calculation of the ground state energy and the spin and string correlation functions. Numerical (Lanczos) calculations of the energies of the ground state and of the low-lying excited states are performed, and compare reasonably with the variational approach. Our results support the hypothesis that the dimer and Majumdar - Ghosh points are in the same phase as the AF S = 1 chain. 相似文献
12.
We investigate the ground state properties of a noncentrosymmetric superconductor near a surface. We determine the spectrum of Andreev bound states due to surface-induced mixing of bands with opposite spin helicities for a Rashba-type spin-orbit coupling. We find that the order parameter suppression qualitatively changes the bound state spectrum. The spin structure of Andreev states leads to a spin supercurrent along the interface, which is strongly enhanced compared to the normal state spin current. Particle and hole coherence amplitudes show Faraday-like rotations of the spin along quasiparticle trajectories. 相似文献
13.
In this Letter we study various spin correlated insulating states of F=2 cold atoms in optical lattices. We find that the effective spin exchange interaction due to virtual hopping contains an octopole coupling between two neighboring lattice sites. Depending on scattering lengths and numbers of particles per site the ground states are either rotationally invariant dimer or trimer Mott insulators or insulating states with various spin orders. Three spin-ordered insulating phases are ferromagnetic, cyclic, and nematic Mott insulators. We estimate the phase boundaries for states with different numbers of atoms per lattice site. 相似文献
14.
Masaaki Nakamura Satoshi Nishimoto 《The European Physical Journal B - Condensed Matter and Complex Systems》2018,91(9):203
We discuss the exact plaquette-ordered ground states of the generalized Hubbard model on the Kagomé lattice for several fillings, by constructing the Hamiltonian as a sum of products of projection operators for up and down spin sectors. The obtained exact ground states are interpreted as Néel ordered states on the bond-located electrons. We determine several parameter regions of the exact ground states, and calculate the entanglement entropy. We examine the above results by numerical calculations based on exact diagonalization and density-matrix renormalization group methods. 相似文献
15.
W.D. Hobey 《Molecular physics》2013,111(4):325-331
In dealing theoretically with the effects of vibronic interactions in substituted benzene mononegative radical-ions it is useful to know the spin density distributions in the degenerate ground level of unsubstituted benzene anions. A configuration interaction theory is developed for hydrocarbon anions with degenerate ground states and applied to the benzene anion problem. The results show negative spin densities on atoms having zero spin density in the Hückel approximation. 相似文献
16.
The spin polarization of the FQHE ground states at fixed filling factors is analyzed within a composite fermion model. As a function of the perpendicular magnetic field several cross‐overs between differently polarized ground states are predicted, in agreement with recent experimental investigations. The magnetic field and temperature scalings of the polarization, as well as the magnetic field dependence of the spin‐flip gap are studied. 相似文献
17.
I. Thorslund C. Fahlander A. Bäcklin B. Kotliński D. Cline A. T. Renalds E. G. Vogt 《Zeitschrift für Physik A Hadrons and Nuclei》1992,342(1):35-42
The lifetimes of five states in the ground band, from spin 6+ up to spin 14+, and of all even states in the gamma band up to spin 12+, have been measured in166Er using the recoil distance method. The reduced electric quadrupole transition probabilities have been determined from the measured lifetimes using previously measured branching ratios, and the mixing between the ground band and theγ-band has been studied. The transitional electric quadrupole moments for the ground band and theγ-band have been deduced and are discussed. 相似文献
18.
C K Majumdar 《Pramana》1985,25(4):505-512
We discuss limitations of the conventional ‘broken symmetry’ picture of the Heisenberg antiferromagnet. The exact results
on the ground state of the linear chain and of the three-dimensional Hamiltonian do not show a ‘degeneracy of the vacuum’.
With the help of a solvable model it is shown that the correlations in the ground state may have the Néel character, as revealed
by the neutron experiments, even though the ground state is quite different from the Néel states. There is no Goldstone mode
in the linear chain. The spin of the antiferromagnetic spin wave is 1/2. But the physical states have a doublet of the spin
waves which could be regarded as degenerate states of spin 1 and spin 0. The fermionic character is suppressed and the bosonic
character revealed, as in the decolouring phenomena in quantum field theory. It is plausible that in the three-dimensional
case also there is no Goldstone mode. 相似文献
19.
We present studies of thermal entanglement of a three-spin system in triangular symmetry. Spin correlations are described within an effective Heisenberg Hamiltonian, derived from the Hubbard Hamiltonian, with super-exchange couplings modulated by an effective electric field. Additionally a homogenous magnetic field is applied to completely break the degeneracy of the system. We show that entanglement is generated in the subspace of doublet states with different pairwise spin correlations for the ground and excited states. For the doublets with the same spin orientation one can observe nonmonotonic temperature dependence of entanglement due to competition between entanglement encoded in the ground state and the excited state. The mixing of the states with an opposite spin orientation or with quadruplets (unentangled states) always monotonically destroys entanglement. Pairwise entanglement is quantified using concurrence for which analytical formulae are derived in various thermal mixing scenarios. The electric field plays a specific role – it breaks the symmetry of the system and changes spin correlations. Rotating the electric field can create maximally entangled qubit pairs together with a separate spin (monogamy) that survives in a relatively wide temperature range providing robust pairwise entanglement generation at elevated temperatures. 相似文献
20.
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