共查询到20条相似文献,搜索用时 15 毫秒
1.
We study the effect of electric field and magnetic flux on spin entanglement in an artificial triangular molecule built of coherently coupled quantum dots. In a subspace of doublet states an explicit relation of concurrence with spin correlation functions and chirality is presented. The electric field modifies superexchange correlations and shifts many-electron levels (the Stark effect), as well as changing spin correlations. For some specific orientation of the electric field one can observe monogamy, for which one of the spins is separated from two others. Moreover, the Stark effect manifests itself in a different spin entanglement for small and strong electric fields. The role of magnetic flux is opposite: it leads to circulation of spin supercurrents and spin delocalization. 相似文献
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I. Sainz G. Burlak A. B. Klimov 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2011,65(3):627-634
Dynamics of the one-dimensional open Ising chain under influence of transverse magnetic field applied in form of π-pulses is studied. It is shown how the application of a specific sequence of such instant kicks to selective spins stimulates arising of perfect dynamical pairwise entanglement between ends of the spin chain. Analytic formulas for the concurrence dynamics are derived. It is also shown that the time required to perfectly entangle the ends of the chains grows linearly with the number of spins in the chain. The effect of the phase decoherence is briefly analyzed. 相似文献
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研究了匀强及非匀强磁场中反铁磁体Heisenberg XXX链的近邻和次近邻纠缠.结果表明对基态情形,纠缠随磁场B变化呈现阶梯型结构,这可用来构建量子纠缠"放大器"或量子纠缠"开关".对有限温度情形,引进一非匀强磁场Bi=(-1)iB可以使近邻格点间纠缠在某些区域明显增大,而次近邻格点间纠缠则完全消失;同时引进非匀强磁场Bi=(-1)iB还可以使近邻格点纠缠的临界温度Tcn增大,且Tcn随B的增大而升高,这意味着我们可以通过调节B的大小而在任意温度下得到纠缠. 相似文献
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We consider N initially disentangled spins, embedded in a ring or d-dimensional lattice of arbitrary geometry, which interact via some long-range Ising-type interaction. We investigate relations between entanglement properties of the resulting states and the distance dependence of the interaction in the limit N-->infinity. We provide a sufficient condition when bipartite entanglement between blocks of L neighboring spins and the remaining system saturates and determine S(L) analytically for special configurations. We find an unbounded increase of S(L) as well as diverging correlation and entanglement length under certain circumstances. For arbitrarily large N, we can efficiently calculate all quantities associated with reduced density operators of up to ten particles. 相似文献
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Hoang Nam Nhat Phung Quoc Thanh Le Thi Anh Thu 《Journal of magnetism and magnetic materials》2009,321(24):4123-4127
The spin chain systems with one-dimensional magnetic ordering are promising candidates for quantum optical devices. This paper shows how the optical excitation can induce various phonon modes in an ideal Cu-O chain at various lengths. The calculation was carried out at different level theories including configuration interaction singles for excited states, density functional theory and second-order Möller-Plesset perturbation. In general, the number of modes increases with chain length due to growing asymmetry of atomic positions when chain exceeds 5 nm. There were, however, only two basic modes: one is associated with the symmetric oscillation of oxygen and another with the asymmetric motion of the same along the chain. At the length below 4.3 nm, the Raman activity of the symmetric mode (440 cm−1) dominates. From analysis of density of states, this mode may be associated with the excitation across the lowest LUMO bands with changing in spin state. 相似文献
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Yu. V. Ivankov M. N. Levin O. A. Ivanova E. Yu. Ivankova 《Bulletin of the Russian Academy of Sciences: Physics》2011,75(2):254-256
The time dependences for a population of radical pair spin states and the amplitudes of the transitions between them are calculated for magnetic fields of complex configuration. The abovementioned values are derived directly from the solution to the Liouville equation for the components of a spin density matrix for a radical pair. The oscillating mechanism of the relaxation of partial populations of spin levels upon the monotonous reduction of the full population was established in the course of our calculations. 相似文献
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An analysis is made of experimental information on the domain-wall mobility in permalloy films in pulsed external fields. Both single pulses and pulse trains, with various temporal parameters, are considered. The experimental results are compared with a solution of the equation of motion for the domain walls.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 2, pp. 64–67, February, 1971. 相似文献
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Using the trion as an optical probe, we uncover novel electron spin dynamics in CdSe/ZnSe Stranski-Krastanov quantum dots. The longitudinal spin lifetime obeys an inverse power law associated with recharging processes in the dot ensemble. No hint at spin-orbit mediated spin relaxation is found. At very weak magnetic fields (< 50 mT), electron spin dynamics related to the hyperfine interaction with the lattice nuclei is uncovered. A strong Knight field gives rise to nuclear ordering and formation of dynamical polarization on a 100-micros time scale under continuous electron spin pumping. The associated spin transients are temperature robust and can be observed up to 100 K. 相似文献
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G. Müller 《Zeitschrift für Physik B Condensed Matter》1987,68(2-3):149-159
The present study highlights some of the complexities observed in the dynamical properties of one-dimensional quantum spin systems. Exact results for zero-temperature dynamic correlation functions are presented for two contrasting situations:
- a system with a fully ordered ferromagnetic ground state;
- a system at aT c=0 critical point.
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Coupled chains in electric and magnetic fields are discussed in terms of interplays between periodicity conditions and the factorization of the wavefunction in the wavenumber representation. Proceeding in this manner yields a quickly tractable matching condition providing the quantization rule to the alternative derivation of complex energy bands. Besides achieving a deeper understanding of Wannier-Stark ladders in terms of complex resonance energies, we now have the opportunity to establish related energy levels by resorting to a suitable conversion technique. This amounts to perform an immediate integration of such energy bands over the Brillouin-zone. Such energy levels exhibit, this time, a safe dependence on the chain parameter. Dynamic localization effects, conserved currents and stripe conductivity formulae have also been discussed. 相似文献
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E. Balcar S. W. Lovesey J. M. Loveluck 《Zeitschrift für Physik B Condensed Matter》1984,54(3):195-199
Low temperature data are given for the spectra of longitudinal and transverse correlation functions of an antiferromagnetic classical heisenberg chain. The one dimensional magnet subjected to large external fields is investigated by means of a computer simulation calculation. The results are tied in with the static properties and compared with theoretical predictions. 相似文献
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A. Seeger 《Hyperfine Interactions》1997,105(1-4):151-159
An exact solution of the Bloch–Torrey equation that covers the entire range of relative diffusivities D between the spin carriers
and the magnetic structure (due to, e.g., spin‐density waves) is given for the transverse relaxation of an initally uniformly
polarized spin system under the influence of a magnetic field varying sinusoidally in space. Explicit closed‐form results
for the short‐time relaxation are obtained making use of Laplace transforms, the three‐term recurrence relations associated
with Mathieu’s equation, and novel sum rules. At intermediate diffusivities the transverse polarization exhibits a novel long‐time
behaviour as a function of D.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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《中国物理 B》2015,(7)
We present our extensive research into magnetic anisotropy. We tuned the terrace width of Si(111) substrate by a novel method: varying the direction of heating current and consequently manipulating the magnetic anisotropy of magnetic structures on the stepped substrate by decorating its atomic steps. Laser-induced ultrafast demagnetization of a Co Fe B/Mg O/Co Fe B magnetic tunneling junction was explored by the time-resolved magneto-optical Kerr effect(TRMOKE) for both the parallel state(P state) and the antiparallel state(AP state) of the magnetizations between two magnetic layers. It was observed that the demagnetization time is shorter and the magnitude of demagnetization is larger in the AP state than those in the P state. These behaviors are attributed to the ultrafast spin transfer between two Co Fe B layers via the tunneling of hot electrons through the Mg O barrier. Our observation indicates that ultrafast demagnetization can be engineered by the hot electron tunneling current. This opens the door to manipulate the ultrafast spin current in magnetic tunneling junctions. Furthermore, an all-optical TR-MOKE technique provides the flexibility for exploring the nonlinear magnetization dynamics in ferromagnetic materials, especially with metallic materials. 相似文献
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Entanglement in quantum spin chains, symmetry classes of random matrices, and conformal field theory
We compute the entropy of entanglement between the first N spins and the rest of the system in the ground states of a general class of quantum spin chains. We show that under certain conditions the entropy can be expressed in terms of averages over ensembles of random matrices. These averages can be evaluated, allowing us to prove that at critical points the entropy grows like kappalog(2N+kappa as N-->infinity, where kappa and kappa are determined explicitly. In an important class of systems, kappa is equal to one-third of the central charge of an associated Virasoro algebra. Our expression for kappa therefore provides an explicit formula for the central charge. 相似文献