共查询到20条相似文献,搜索用时 31 毫秒
1.
In this paper,a variable separation approach is used to obtain localized coherent structures of the (2 1)-dimensional generalized nonlinear Schroedinger equation:Iφt-(α-β)φxx (α β)φyy-2λφ[(α β)(∫-∞^x|φ|y^2ydx u1(y,t))-(α-β)(∫-∞^y|φ|x^2dy u2(x,t))]=0,By applying a special Baecklund transformation and introducing arbitrary functions of the seed solutions,the abundance of the localized structures of this model are derived.By selecting the arbitrary function appropriately,some special types of localized excitations such as dromions,dromion lattice,breathers and istantons are constructed. 相似文献
2.
Using the coherent state representation of Wigner operator and the technique of integration within an ordered product (IWOP) of operators, this paper derives the Wigner functions for the photon-depleted even and odd coherent states (PDEOCSs). Moreover, in terms of the Wigner functions with respect to the complex parameter a the nonclassical properties of the PDEOCSs are discussed. The results show that the nonclassicality for the state |β, m〉o (or |β,m〉e) is more pronounced when m is even (or odd). According to the marginal distributions of the Wigner functions, the physical meaning of the Wigner functions is given. Further, the tomograms of the PDEOCSs are calculated with the aid of newly introduced intermediate coordinate-momentum representation in quantum optics. 相似文献
3.
We have considered two distant mesoscopic superconducting quantum
interference device (SQUID) rings A and B in the presence of two-mode
nonclassical state fields and investigated the correlation of the
supercurrents in the two rings using the normalized correlation
function $C_{\rm AB}$. We show that when the parameter $\alpha$ is
very small for the separable state with the density matrix $\hat
{\rho } = (\left| {\alpha , - \alpha } \right\rangle \left\langle
{\alpha , - \alpha } \right| + \left| { - \alpha ,\alpha }
\right\rangle \left\langle { - \alpha ,\alpha } \right|) / 2$ and
entangled coherent state (ECS) $\left| u \right\rangle = N_1 (\left|
{\alpha , - \alpha } \right\rangle + \left| { - \alpha ,\alpha }
\right\rangle )$ fields, the dynamic behaviours of the normalized
correlation function $C_{\rm AB}$ are similar, but it is quite
different for the entangled coherent state $\left| {u}'
\right\rangle = N_2 (\left| {\alpha , - \alpha } \right\rangle -
\left| { - \alpha ,\alpha } \right\rangle )$ field. When the
parameter $\alpha $ is very large, the dynamic behaviours of $C_{\rm
AB}$ are almost the same for the separable state, entangled coherent
state $\left| u \right\rangle $ and $\left| {u}' \right\rangle $
fields. For the two-mode squeezed vacuum state field the maximum of
$C_{\rm AB}$ increases monotonically with the squeezing parameter
$r$, and as $r \to \infty $, $C_{\rm AB} \to 1$. This means that the
supercurrents in the two rings A and B are quantum mechanically
correlated perfectly. It is concluded that not all the quantum
correlations in the two-mode nonclassical state field can be
transferred to the supercurrents; and the transfer depends on the
state of the two-mode nonclassical state field prepared. 相似文献
4.
By introducing the s-parameterized generalized Wigner operator into phase-space quantum mechanics we invent the technique of integration within s-ordered product of operators(which considers normally ordered,antinormally ordered and Weyl ordered product of operators as its special cases).The s-ordered operator expansion(denoted by...) formula of density operators is derived,which is ρ = 2 1 s ∫ d2βπβ|ρ |β exp { 2 s 1(s|β|2 β a + βa a a) }.The s-parameterized quantization scheme is thus completely established. 相似文献
5.
By introducing a kind of new quantum state—Photon-added thermo invariant coherent state (PATCS), we discuss its nonclassicality
in terms of the negativity of Wigner function (WF) after deriving its analytical expression. It is found that the Wigner function
is related to Lagurre-Gaussian function. We then study the effect of decoherence (a thermal environment) on the PATCS according
to its WF (also related to Lagurre-Gaussian function). It is shown that it is not possible for WF to present the negative
region when the decay time
$\kappa t>\frac{1}{2}\ln \frac{2\bar{n}+2}{2\bar{n}+1}$\kappa t>\frac{1}{2}\ln \frac{2\bar{n}+2}{2\bar{n}+1}
. 相似文献
6.
Optical NOON states ${{\left( {\left| {\left. {N,0} \right\rangle + } \right|\left. {0,N} \right\rangle } \right)} \mathord{\left/
{\vphantom {{\left( {\left| {\left. {N,0} \right\rangle + } \right|\left. {0,N} \right\rangle } \right)} {\sqrt 2 }}} \right.
\kern-\nulldelimiterspace} {\sqrt 2 }}${{\left( {\left| {\left. {N,0} \right\rangle + } \right|\left. {0,N} \right\rangle } \right)} \mathord{\left/
{\vphantom {{\left( {\left| {\left. {N,0} \right\rangle + } \right|\left. {0,N} \right\rangle } \right)} {\sqrt 2 }}} \right.
\kern-\nulldelimiterspace} {\sqrt 2 }} are an important resource for Heisenberg-limited metrology and quantum lithography. The only known methods for creating NOON
states with arbitrary N via linear optics and projective measurements seem to have a limited range of application due to imperfect phase control.
Here, we show that bootstrapping techniques can be used to create high-fidelity NOON states of arbitrary size. 相似文献
7.
We consider the block band matrices, i.e. the Hermitian matrices $H_N$ , $N=|\Lambda |W$ with elements $H_{jk,\alpha \beta }$ , where $j,k \in \Lambda =[1,m]^d\cap \mathbb {Z}^d$ (they parameterize the lattice sites) and $\alpha , \beta = 1,\ldots , W$ (they parameterize the orbitals on each site). The entries $H_{jk,\alpha \beta }$ are random Gaussian variables with mean zero such that $\langle H_{j_1k_1,\alpha _1\beta _1}H_{j_2k_2,\alpha _2\beta _2}\rangle =\delta _{j_1k_2}\delta _{j_2k_1} \delta _{\alpha _1\beta _2}\delta _{\beta _1\alpha _2} J_{j_1k_1},$ where $J=1/W+\alpha \Delta /W$ , $\alpha < 1/4d$ . This matrices are the special case of Wegner’s $W$ -orbital models. Assuming that the number of sites $|\Lambda |$ is finite, we prove universality of the local eigenvalue statistics of $H_N$ for the energies $|\lambda _0|< \sqrt{2}$ . 相似文献
8.
In this paper the superpositions of two arbitrary coherent states |ψ〉 = α |β| + be^iψ |mβe^iδ〉 are constructed by using the superposition principle of quantum mechanics. The entropic squeezing effects of the quantum states are studied. The numerical results indicate that the amplitudes, the ratio between the amplitudes of two coherent states, the phase difference between the two components and the relative phase of the two coefficients play important roles in the squeezing effects of the position entropy and momentum entropy. 相似文献
9.
In this paper, we study the decoherence of quantum excitation (photon-added) even /odd coherent states, \(((\hat a{^{\dagger }})^{m} \left | {\alpha _ \pm } \right \rangle )\), in a thermal environment by investigating the variation of negative part of the Wigner quasidistribution function vs. the rescaled time. For this purpose, at first we obtain the time-dependent Wigner function corresponding to the mentioned states in the framework of standard master equation. Then, the time evolution of the Wigner function associated with photon-added even /odd coherent states, as well as the number of added photons m are analysed. It is shown that, in both states, the negative part of the Wigner function decreases with time. By deriving the threshold value of the rescaled time for single photon-added even /odd coherent states, it is also found that, if the rescaled time exceeds the threshold value, the associated Wigner function becomes positive, i.e., the decoherence occurs completely. 相似文献
10.
The dynamic behaviours of the translocations of closed circular polymers and closed knotted polymers through a nanopore, under the driving of an applied field, are studied by three-dimensional Langevin dynamics simulations. The power-law scaling of the translocation time τ with the chain length N and the distribution of translocation time are investigated separately. For closed circular polymers, a crossover scaling of translocation time with chain length is found to be τ~ N α , with the exponent α varying from α = 0.71 for relatively short chains to α = 1.29 for longer chains under driving force F = 5. The scaling behaviour for longer chains is in good agreement with experimental results, in which the exponent α = 1.27 for the translocation of double-strand DNA. The distribution of translocation time D(τ) is close to a Gaussian function for duration time τ < τ p and follows a falling exponential function for duration time τ > τ p . For closed knotted polymers, the scaling exponent α is 1.27 for small field force (F = 5) and 1.38 for large field force (F = 10). The distribution of translocation time D(τ) remarkably features two peaks appearing in the case of large driving force. The interesting result of multiple peaks can conduce to the understanding of the influence of the number of strands of polymers in the pore at the same time on translocation dynamic process and scaling property. 相似文献
11.
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.
研究了由光子增减叠加操作作用于相干态而得量子态的非经典性及其在热环境中的退相干问题.通过解析导出了Mandel's Q参数、光子数分布、Wigner函数等,讨论其非经典性.研究表明一阶光子增减相干叠加相干态在相空间总是取负值,只要满足条件∣2z* +α-α*∣2<1.基于Wigner函数的演化积分公式,解析地推导出了在热环境中Wigner函数的简洁表达式.研究首次表明:如果κt<1/2ln[(2(η)+2)/(2(η)+1)]得以满足,一阶光子增减相干叠加相干态在相空间最小值点处Wigner函数分布总存在负部.此外,根据Wigner函数负部体积讨论了其非经典特性. 相似文献
13.
The Raman-coupled interaction between an atom and a single mode of a cavity field is studied. For the cases in which a light field is initially in a coherent state and in a thermal state separately, we have derived the analytic expressions for the time evolutions of atomic population difference W, modulus B of the Bloch vector, and entropy E. We find that the time evolutions of these quantities are periodic with a period of π. The maxima of W and B appear at the scaled interaction time points τ- = kπ(k = 0, 1, 2,...). At these time points, E = 0, which shows that the atom and the field are not entangled. Between these time points, E ≠ 0, which means that the atom and the field are entangled. When the field is initially in a coherent state, near the maxima, the envelope of W is a Gaussian function with a variance of 1/(4n^-)(n^- is the mean number of photons). Under the envelope, W oscillates at a frequency of n^-/π. When the field is initially in a thermal state, near the maxima, W is a Lorentz function with a width of 1/n^-. 相似文献
14.
We study amplitude-squared squeezing of the Hermitian operator Z θ=Z 1
cosθ+Z 2 sin θ, in the most general superposition state
, of two coherent states
and
. Here operators Z 1,2 are defined by
, a is annihilation operator, θ is angle, and
complex numbers C 1,2 , α, β are arbitrary and only
restriction on these is the normalization condition of the state
. We define the condition for a state
to be amplitude-squared squeezed for the operator Z θ
if squeezing parameter
, where N=a +a and
. We find
maximum amplitude-squared squeezing of Z θ in the superposed
coherent state
with minimum value 0.3268 of the
parameter S for an infinite combinations with α- β= 2.16
exp [±i(π/4) + iθ/2],
and with
arbitrary values of (α+β) and θ. For this minimum
value of squeezing parameter S, the expectation value of photon number can
vary from the minimum value 1.0481 to infinity. Variations of the parameter
S with different variables at maximum amplitude-squared squeezing are also
discussed. 相似文献
15.
Phase space analysis of quantum states is a newly developed topic in quantum optics. In this work we present Wigner phase space distributions for the two-mode binomial state produced by quantum entanglement between a vacuum state and a number state in a beamsplitter. By using two new binomial formulas involving two-variable Hermite polynomials and the so-called entangled Wigner operator, we find that the analytical Wigner function for the binomial state |ξ〉q ≡ D(ξ) |q, 0〉 is related to a Laguerre polynomial, i.e.,
$ W\left (\sigma _{,}\gamma \right ) =\frac {(-1)^{q}e^{-\left \vert \gamma \right \vert ^{2}-\left \vert \sigma \right \vert ^{2}}}{\pi ^{2}}L_{q}\left (\left \vert \frac {-\varsigma (\sigma -\gamma )+\sigma ^{\ast }+\gamma ^{\ast }} {\sqrt {1+|\varsigma |^{2}}}\right \vert ^{2}\right ) $and its marginal distributions are proportional to the module-square of a single-variable Hermite polynomial. Also, the numerical results show that the larger number sum q of two modes lead to the stronger interference effect and the nonclassicality of the states |ξ〉q is stronger for odd q than for even q. 相似文献
16.
In this paper we study the Liouville-type properties for solutions to the steady incompressible Euler equations with forces in ${\mathbb {R}^N}$ . If we assume “single signedness condition” on the force, then we can show that a ${C^1 (\mathbb {R}^N)}$ solution ( v, p) with ${|v|^2+ |p| \in L^{\frac{q}{2}}(\mathbb {R}^N),\,q \in (\frac{3N}{N-1}, \infty)}$ is trivial, v = 0. For the solution of the steady Navier–Stokes equations, satisfying ${v(x) \to 0}$ as ${|x| \to \infty}$ , the condition ${\int_{\mathbb {R}^3} |\Delta v|^{\frac{6}{5}} dx < \infty}$ , which is stronger than the important D-condition, ${\int_{\mathbb {R}^3} |\nabla v|^2 dx < \infty}$ , but both having the same scaling property, implies that v = 0. In the appendix we reprove Theorem 1.1 (Chae, Commun Math Phys 273:203–215, 2007), using the self-similar Euler equations directly. 相似文献
17.
Monoclinic $\alpha $-MoP$_{2}$, with the OsGe$_{2}$-type structure (space group $C2/m$, $Z = 4$) and lattice parameters $a = 8.7248(11) $ Å, $b = 3.2322(4) $ Å, $c = 7.4724(9) $ Å, and $\beta =119.263^\circ $, was synthesized under a pressure of 4 GPa at a temperature between 1100 ${^\circ}$C and 1200 ${^\circ}$C. The structure of $\alpha $-MoP$_{2}$ and its relationship to other transition metal diphosphides are discussed. Surprisingly, the ambient pressure phase orthorhombic $\beta $-MoP$_{2}$ (space group Cmc2$_{1}$) is denser in structure than $\alpha $-MoP$_{2}$. Room-temperature high-pressure x-ray diffraction studies exclude the possibility of phase transition from $\beta $-MoP$_{2}$ to $\alpha $-MoP$_{2}$, suggesting that $\alpha $-MoP$_{2}$ is a stable phase at ambient conditions; this is also supported by the total energy and phonon calculations. 相似文献
18.
We propose modified frequentist definition for the determination of confidence intervals for the case of Poisson statistics. Namely, we require that $1 - \beta ' \geqslant \sum\nolimits_{n = 0}^{n = n_{obs} + k} {P\left( {\left. n \right|\lambda } \right)} \geqslant \alpha '$ . We show that this definition is equivalent to the Bayesian method with prior π(λ) ~ λ k . We also propose modified frequentist definition for the case of nonzero background. 相似文献
19.
We consider the spectrum of the quantum Hamiltonian H for a system of N one-dimensional particles. H is given by $H = \sum\nolimits_{i = 1}^n { - \frac{1}{{2m_i }}\frac{{\partial ^2 }}{{\partial x_i^2 }}} + \sum {_{1 \leqslant i < j \leqslant N} } V_{ij} \left( {x_i - x_j } \right)$ acting in L 2( R N ). We assume that each pair potential is a sum of a hard core for | x|≤ a, a>0, and a function V ij ( x), | x|> a, with $\smallint _a^\infty \left| {x - a} \right|\left| {V_{ij} \left( x \right)} \right|dx < \infty $ . We give conditions on V ? ij ( x), the negative part of V ij ( x), which imply that H has no negative energy spectrum for all N. For example, this is the case if V ? ij ( x) has finite range 2a and $$2m_i \smallint _a^{2a} \left| {x - a} \right|\left| {V_{ij}^ - \left( x \right)} \right|dx < 1.$$ If V ? ij is not necessarily small we also obtain a thermodynamic stability bound inf? σ( H)≥? cN, where 0< c<∞, is an N-independent constant. 相似文献
20.
Like the coordinate projector | q〉〈 q|= δ( q? Q), where Q is coordinate operator, we find that $\pi\delta( \eta_{1}-\frac{Q_{1}-Q_{2}}{\sqrt{2}}) \delta( \eta_{2}-\frac{P_{1}+P_{2}}{\sqrt{2}}) $ is an entangled projector | η〉〈 η|, where | η〉 is the bipartite entangled state and η= η 1+ iη 2. We then derive the entangled Wigner operator in terms of the properties of the entangled projector. This seems a new approach for obtaining the entangled Wigner operator. 相似文献
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