共查询到20条相似文献,搜索用时 31 毫秒
1.
We study the structure of maps that Lorentz boosts induce on the spin degree of freedom of a system consisting of two massive spin-1/2 particles. We consider the case where the spin state is described by the Werner state and the momenta are discrete. Transformations on the spins are systematically investigated in various boost scenarios by calculating the orbit and concurrence of the bipartite spin state with different kinds of product and entangled momenta. We confirm the general conclusion that Lorentz boosts cause non-trivial behavior of bipartite spin entanglement. Visualization of the evolution of the spin state is shown to be valuable in explaining the pattern of concurrence. The idealized model provides a basis of explanation in terms of which phenomena in systems involving continuous momenta can be understood. 相似文献
2.
We study the properties of quantum entanglement in moving frames, and show that, because spin and momentum become mixed when viewed by a moving observer, the entanglement between the spins of a pair of particles is not invariant. We give an example of a pair, fully spin entangled in the rest frame, which has its spin entanglement reduced in all other frames. Similarly, we show that there are pairs whose spin entanglement increases from zero to maximal entanglement when boosted. While spin and momentum entanglement separately are not Lorentz invariant, the joint entanglement of the wave function is. 相似文献
3.
4.
K. Berrada Y. Hassouni 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2011,61(2):513-521
In the framework of the U
q
(su(2)) quantum algebra, we
investigate the entanglement properties of two-spin systems, of
arbitrary spins j
1 and j
2, defined in an entanglement of
deformed spin coherent states of each of the spins. We derive the
amount of entanglement and we give conditions under which bipartite
entangled states become maximally entangled. Using these conditions,
we construct a large class of Bell states for any choices of the
parameters that specify the spin coherent states. 相似文献
5.
We study the properties of quantum entanglement in moving frames, with a non-maximally entangled bipartite state: $|\phi\rangle=\sqrt{1-\varepsilon}|{\uparrow\uparrow}\rangle +\sqrt{\varepsilon}|{\downarrow\downarrow}\rangle$ , (0<ε<1). We calculate the concurrence of this state under Lorentz transformation and show that if the momenta part of the spin-1/2 pair is appropriately correlated, the concurrence is invariant ( $\mathcal {C}(\rho)=2\sqrt{\varepsilon-\varepsilon^{2}}$ ); despite the entanglement of this state is not maximal, there is no transfer of entanglement between spin and momentum. 相似文献
6.
A. Fubini T. Roscilde V. Tognetti M. Tusa P. Verrucchi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,38(3):563-570
We consider a quantum many-body system made of N interacting
S=1/2 spins on a lattice, and develop a formalism which allows to
extract, out of conventional magnetic observables, the quantum
probabilities for any selected spin pair to be in maximally entangled
or factorized two-spin states. This result is used in order to
capture the meaning of entanglement properties in terms of magnetic
behavior. In particular, we consider the concurrence between two
spins and show how its expression extracts information on the presence
of bipartite entanglement out of the probability distributions
relative to specific sets of two-spin quantum states. We apply the
above findings to the antiferromagnetic Heisenberg model in a uniform
magnetic field, both on a chain and on a two-leg ladder. Using Quantum
Monte Carlo simulations, we obtain the above probability distributions
and the associated entanglement, discussing their evolution under
application of the field. 相似文献
7.
ChuanMei Xie YiMin Liu JianLan Chen XiaoFeng Yin ZhanJun Zhang 《中国科学:物理学 力学 天文学(英文版)》2016,59(10):100314
In this paper, the issue of swapping quantum entanglements in two arbitrary biqubit pure states via a local bipartite entangledstate projective measure in the middle node is studied in depth, especially with regard to quantitative aspects. Attention is mainly focused on the relation between the measure and the final entanglement obtained via swapping. During the study, the entanglement of formation (EoF) is employed as a quantifier to characterize and quantify the entanglements present in all involved states. All concerned EoFs are expressed analytically; thus, the relation between the final entanglement and the measuring state is established. Through concrete analyses, the measure demands for getting a certain amount of a final entanglement are revealed. It is found that a maximally entangled final state can be obtained from any two given initial entangled states via swapping with a certain probability; however, a peculiar measure should be performed. Moreover, some distinct properties are revealed and analyzed. Such a study will be useful in quantum information processes. 相似文献
8.
M. Mahdian B. Mojaveri A. Dehghani T. Makaremi 《International Journal of Theoretical Physics》2016,55(2):678-697
We study the quantum correlation dynamics of bipartite spin-\(\frac {1}{2}\) density matrices for two particles under Wigner rotations induced by Lorentz transformations which is transmitted through noisy channels. We compare quantum entanglement, geometric discord(GD), and quantum discord (QD) for bipartite relativistic spin-\(\frac {1}{2}\) states under noisy channels. We find out QD and GD tend to death asymptotically but a sudden change in the decay rate of the entanglement occurs under noisy channels. Also, bipartite relativistic spin density matrices are considered as a quantum channel for teleportation one-qubit state under the influence of depolarizing noise and compare fidelity for various velocities of observers. 相似文献
9.
In this paper we obtain violations of general bipartite Bell inequalities of order \({\frac{\sqrt{n}}{\log n}}\) with n inputs, n outputs and n-dimensional Hilbert spaces. Moreover, we construct explicitly, up to a random choice of signs, all the elements involved in such violations: the coefficients of the Bell inequalities, POVMs measurements and quantum states. Analyzing this construction we find that, even though entanglement is necessary to obtain violation of Bell inequalities, the entropy of entanglement of the underlying state is essentially irrelevant in obtaining large violation. We also indicate why the maximally entangled state is a rather poor candidate in producing large violations with arbitrary coefficients. However, we also show that for Bell inequalities with positive coefficients (in particular, games) the maximally entangled state achieves the largest violation up to a logarithmic factor. 相似文献
10.
Entangled photon-pair sources based on spontaneous parametric processes are widely used in photonic quantum information experiments. In this paper, we clarify the relationship between average photon-pair number and the visibility of two-photon interference (TPI) using those entanglement sources. We consider sources that generate distinguishable and indistinguishable entangled photon pairs, assuming coincidence measurements that use threshold detectors. We present formulas for the TPI visibility of a polarization entanglement that take account of all the high-order multi-pair emission events. Moreover, we show that the formulas can be approximated with simple functions of the average pair number when the photon collection efficiency is small. As a result, we reveal that an indistinguishable entangled pair provides better visibility than a distinguishable one. 相似文献
11.
H. Mohammadi S. J. Akhtarshenas F. Kheirandish 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2011,62(3):439-447
We study the entanglement dynamics of an anisotropic two-qubit Heisenberg XYZ system in
the presence of intrinsic decoherence. The usefulness of such a system for performance of
the quantum teleportation protocol T0\mathcal{T}_0
and entanglement teleportation protocol T1\mathcal{T}_1
is also investigated. The results depend on the initial conditions and the parameters of
the system. The roles of system parameters such as the inhomogeneity of the magnetic field
b and the spin-orbit interaction parameter D, in
entanglement dynamics and fidelity of teleportation, are studied for both product and
maximally entangled initial states of the resource. We show that for the product and
maximally entangled initial states, increasing D amplifies the effects of
dephasing and hence decreases the asymptotic entanglement and fidelity of the
teleportation. For a product initial state and specific interval of the magnetic field
B, the asymptotic entanglement and hence the fidelity of teleportation
can be improved by increasing B. The XY and XYZ Heisenberg systems
provide a minimal resource entanglement, required for realizing efficient teleportation.
Also, in the absence of the magnetic field, the degree of entanglement is preserved for
the maximally entangled initial states $\left| {\psi \left. {\left( 0 \right)} \right\rangle = \frac{1}
{{\sqrt 2 }}\left( {\left| {\left. {00} \right\rangle \pm } \right|\left. {11} \right\rangle } \right)} \right.$\left| {\psi \left. {\left( 0 \right)} \right\rangle = \frac{1}
{{\sqrt 2 }}\left( {\left| {\left. {00} \right\rangle \pm } \right|\left. {11} \right\rangle } \right)} \right.. The
same is true for the maximally entangled initial states
$\left| {\psi \left. {\left( 0 \right)} \right\rangle = \frac{1}
{{\sqrt 2 }}\left( {\left| {\left. {01} \right\rangle \pm } \right|\left. {10} \right\rangle } \right)} \right.$\left| {\psi \left. {\left( 0 \right)} \right\rangle = \frac{1}
{{\sqrt 2 }}\left( {\left| {\left. {01} \right\rangle \pm } \right|\left. {10} \right\rangle } \right)} \right., in the
absence of spin-orbit interaction D and the inhomogeneity parameter
b. Therefore, it is possible to perform quantum teleportation protocol
T0\mathcal{T}_0
and entanglement teleportation T1\mathcal{T}_1,
with perfect quality, by choosing a proper set of parameters and employing one of these
maximally entangled robust states as the initial state of the resource. 相似文献
12.
This paper proposes a feasible scheme for the quantum teleportation
of tripartite entangled coherent states by using linear optical
devices such as beam splitters, phase shifters and photo detectors.
The scheme is based on the bipartite maximally entangled coherent
state and the tripartite entangled coherent state with bipartite
maximal entanglement as quantum channels. It shows that when the
mean number of photons is equal to 2, the total minimum of the average
fidelity for an arbitrary tripartite entangled state is 1-0.67×10 -3. 相似文献
13.
K. Maruyama 《Optics and Spectroscopy》2010,108(2):301-304
We present a simple protocol to purify bipartite entanglement in spin-1/2 particles by utilising only natural spin-spin interactions,
i.e., those that can commonly be realised in realistic physical systems, and S
z
-measurements on single spins. Even the standard isotropic Heisenberg interaction is shown to be sufficient to purify mixed
state entanglement if there are at least three pairs of spins. This approach could be useful for quantum information processing
in solid-state-based systems. 相似文献
14.
The fact that spin–momentum of massive particles become entangled (disentangled) as seen by moving observers, is used to investigate the properties of von Neumann entropy, as a measure of spin–momentum entanglement. To do so, we partition the total Hilbert space into momentum and spin subspaces so that the entanglement occurs between total spin states and total momenta of two spin- $\frac{1}{2}$ particles. Assuming that the occurrence of spin–momentum states is determined by Gaussian probability distributions, we show that the degree of entanglement ascends for small rapidities, reaches a maximum and diminishes at high rapidity. We further report how the characteristics of this behaviour vary as the widths of distributions change. In particular, a separable state, resulting from equal distribution widths, indeed becomes entangled in moving frames. 相似文献
15.
We propose a probabilistic scheme for realizing teleportation of bipartite photonic states using linear optical elements where only requires a two-photon Bell state used as quantum channel. It reduces the requirement of the entanglement of quantum channel, but requires an additional photon and an auxiliary maximally entangled photon pair locally. 相似文献
16.
DONG Ping LIN Ji-Cheng YANG Ming CAO Zhuo-Liang 《理论物理通讯》2006,46(4):627-630
We propose a probabilistic scheme for realizing teleportation of bipartite photonic states using linear optical elements where only requires a two-photon Bell state used as quantum channel. It reduces the requirement of the entanglement of quantum channel, but requires an additional photon and an auxiliary maximally entangled photon pair locally. 相似文献
17.
With the consideration of three-body interaction, dynamics of pairwise entanglement in spin chains is studied. The dependence of pairwise entanglement dynamics on the type of coupling, and distance between the spins is analyzed in a finite chain for different initial states. It is found that, for an Ising chain, three-body interactions are not in favor of preparing entanglement between the nearest neighbor spins, while three-body interactions are favorable for creating entanglement between remote spins from a separable initial state. For an isotropic Heisenberg chain, the pairwise concurrence will decrease when three-body interactions are considered both for a separable initial state and for a maximally entangled initial state, however, three-body interactions will retard the decay of the concurrence in an Ising chain when the initial state takes the maximally entangled state. 相似文献
18.
Kevin Ann 《Physics letters. A》2008,372(5):579-583
We demonstrate the existence of entanglement sudden death (ESD), the complete loss of entanglement in finite time, in qubit-qutrit systems. In particular, ESD is shown to occur in such systems initially prepared in a one-parameter class of entangled mixed states and then subjected to local dephasing noise. Together with previous results, this proves the existence of ESD for some states in all quantum systems for which rigorously defined mixed-state entanglement measures have been identified. We conjecture that ESD exists in all quantum systems prepared in appropriate bipartite states. 相似文献
19.
In a recent paper—F. Ciccarello et al., New J. Phys. 8, 214 (2006)—we have demonstrated that the electron transmission properties of a one-dimensional (1D) wire with two identical embedded spin-1/2 impurities can be significantly affected by entanglement between the spins of the scattering centers. Such an effect is of particular interest in the control of the transmission of quantum information in nanostructures and can be used as a detection scheme of maximally entangled states of two localized spins. In this letter, we relax the constraint that the two magnetic impurities are equal and investigate how the main results presented in the above paper are affected by a static disorder in the exchange coupling constants of the impurities. Good robustness against deviation from impurity symmetry is found for both the entanglement dependent transmission and the maximally entangled states generation scheme. 相似文献
20.
Bell state measurements, in which two quantum bits are projected onto a maximally entangled state, are an essential component of quantum information science. We propose and experimentally demonstrate the projection of two quantum systems with three states (qutrits) onto a generalized maximally entangled state. Each qutrit is represented by the polarization of a pair of indistinguishable photons-a biphoton. The projection is a joint measurement on both biphotons using standard linear optics elements. This demonstration enables the realization of quantum information protocols with qutrits, such as teleportation and entanglement swapping. 相似文献