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1.
The transfer of the quantum correlation from two-mode nonclassical state field to the supercurrents in two distant SQUID rings 下载免费PDF全文
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
2.
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
3.
《中国物理 B》2021,30(7):70601-070601
Caesium atomic fountain clock is a primary frequency standard, which realizes the duration of second. Its performance is mostly dominated by the frequency accuracy, and the C-field induced second-order Zeeman frequency shift is the major effect, which limits the accuracy improvement. By applying a high-precision current supply and high-performance magnetic shieldings, the C-field stability has been improved significantly. In order to achieve a uniform C-field, this paper proposes a doubly wound C-field solenoid, which compensates the radial magnetic field along the atomic flight region generated by the lead-out single wire and improves the accuracy evaluation of second-order Zeeman frequency shift. Based on the stable and uniform C-field, we launch the selected atoms to different heights and record the magnetically sensitive Ramsey transition|F = 3, mF=-1 → |F = 4, mF=-1 central frequency, obtaining this frequency shift as 131.03×10~(-15) and constructing the C-field profile(σ = 0.15 n T). Meanwhile, during normal operation, we lock NTSC-F2 to the central frequency of the magnetically sensitive Ramsey transition |F = 3, mF=-1 → |F = 4, mF=-1 fringe for ten consecutive days and record this frequency fluctuation in time domain. The first evaluation of second-order Zeeman frequency shift uncertainty is 0.10×10~(-15). The total deviation of the frequency fluctuation on the clock transition induced by the C-field instability is less than 2.6×10~(-17). Compared with NTSC-F1, NTSC-F2, there appears a significant improvement. 相似文献
4.
The fidelity of the generated Schrdinger Cat state(SCS) of a single trapped ion in the Lamb-Dicke approximation is discussed.The results show that the fidelity significantly decreases with the values of Lamb-Dicke parameter η and coherent state amplitude α increasing.For η = 0.20 and α = 3,the typical values of experimental parameters,the fidelity is rather low(30%).A scheme for generating the SCS is proposed without making the Lamb-Dike approximation in laser-ion interaction,and the fidelity of the generated SCS is about 99% for the typical values of experimental Lamb-Dicke parameters. 相似文献
5.
In this paper, we study the Wigner function of coherent state of N components, especially two components and three components. This function consists of two terms: the Gaussian term and the interference term with the negativity. The first term comprises N Gaussian surfaces evenly centred on a circle of radius |β| = |α| with a separate angle of 2π/N, and the second term is composed of 1/2N(N - 1) Gaussian-cosine surfaces evenly centred in a circular region of radius |β| 〈 |α|. Here, a is the eigenvalue of the annihilation operator α, and β is a variable in some complex space in which the Wigner function is defined. We have proved that the essential condition to eliminate the negativity of the Wigner function is that the mean photon count of the coherent state is equal to that of the Glouber coherent state. 相似文献
6.
H. Prakash P. Kumar 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,46(2):359-363
We study amplitude-squared squeezing of the Hermitian operator Zθ=Z1
cosθ+Z2 sin θ, in the most general superposition state
, of two coherent states
and
. Here operators Z1,2 are defined by
, a is annihilation operator, θ is angle, and
complex numbers C1,2 , 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 Zθ
if squeezing parameter
, where N=a+a and
. We find
maximum amplitude-squared squeezing of Zθ 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
7.
Xiaoling Ji Yuan Ma Zhengcai Pu Xiaoqing Li 《Applied physics. B, Lasers and optics》2014,115(3):379-390
In this paper, taking the tilted and off-axis partially coherent beams as the active detection laser beams, the characteristics of the active detection laser beams reflected back by a cat-eye optical lens in atmospheric turbulence are studied analytically and numerically. The analytical expressions for the centroid position deviation γ, the average intensity, the mean-squared beam width and the far-field divergence angle at the receiver plane are derived. It is found that tilted and off-axis active detection laser beams cannot be reflected back by a cat-eye optical lens in the direction of the source. The absolute deviation $\left| \gamma \right|$ decreases as the beam coherence decreases. Therefore, partially coherent beams are more suitable as active detection laser beams than fully coherent ones. In addition, $\left| \gamma \right|$ decreases greatly due to the aperture effect, and the influence of turbulence on $\left| \gamma \right|$ is not monotonic. On the other hand, the influence of the beam coherence and the atmospheric turbulence on the average intensity, the mean-squared beam width and the far-field divergence angle at the receiver plane is also examined, and some interesting results are obtained. The results obtained in this paper are very useful for applications of the active laser detection. 相似文献
8.
Quantum key distribution transmitter chip based on hybrid-integration of silica and lithium niobates 下载免费PDF全文
A quantum key distribution transmitter chip based on hybrid-integration of silica planar light-wave circuit (PLC) and lithium niobates (LN) modulator PLC is presented. The silica part consists of a tunable directional coupler and 400-ps delay line, and the LN part is made up of a Y-branch, with electro-optic modulators on both arms. The two parts are facet-coupled to form an asymmetric Mach-Zehnder interferometer. We successfully encode and decode four BB84 states at 156.25-MHz repetition rate. Fast phase-encoding of 0 or $\pi $ is achieved, with interference fringe visibilities 78.53% and 82.68% for states $|+\rangle$ and $|-\rangle$, respectively. With the aid of an extra off-chip LN intensity modulator, two time-bin states are prepared and the extinction ratios are 18.65 dB and 15.46 dB for states $|0\rangle$ and $|1\rangle$, respectively. 相似文献
9.
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
10.
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
11.
Finite-dimensional even and odd nonlinear pair coherent states and their some nonclassical properties 下载免费PDF全文
In this paper a new class of finite-dimensional even and odd nonlinear pair coherent states (EONLPCSs), which can be realized via operating the superposed evolution operators D±(τ) on the state |q, 0), is constructed, then their orthonormalized property, completeness relations and some nonclassical properties are discussed. It is shown that the finite-dimensional EONLPCSs possess normalization and completeness relations. Moreover, the finite-dimensional EONLPCSs exhibit remarkably different sub-Poissonian distributions and phase probability distributions for different values of parameters q, η and ξ. 相似文献
12.
Investigations of the electron paramagnetic resonance parameters and the tetragonal local structure for (VCl6)4- coordination complex in MCl:V2+ (M=Na, K, Rb) systems 下载免费PDF全文
By simulating the electron paramagnetic resonance (EPR) and optical spectra on the basis of the 120×120 complete energy matrix, this paper determines the local lattice structure parameters R1 and R2 for MCl:V2+ (M=Na, K, Rb) systems at 77 K, 195 K and RT (room temperature 295 K or 302 K), respectively. The theoretical results indicate that there exists a compressed distortion in MCl:V2+ systems. Meanwhile, it finds that the structure parameters R1, R2 and |△R| (= R1-R2) increase with the rising temperature. Subsequently, from the analysis it concludes that the relation of EPR parameter D vs.△R is approximately linear. Finally, the effects of orbital reduction factor k on the g factors for the three systems have been discussed. 相似文献
13.
This paper investigates the relationship between the speed of a quantum not gate and the asymmetry of the potential in an interactive system formed by a two-level RF-SQUID qubit and a classical microwave pulse. The RFSQUID is characterized by an asymmetric double well potential which gives rise to diagonal matrix elements that describe the interaction of the SQUID with the microwave pulse. And the diagonal matrix elements account for the interaction of the microwave pulse with the SQUID. The results indicate that, when the angular frequency of the microwave field is chosen as near resonate with the transition (0) ←→ (1), i.e. ω1 -ω0 ≈ ωm, (1) the gate speed is decided by three factors, the Rabi frequency, the difference of the diagonal matrix elements between the two levels, and the angular frequency of the applied microwave pulse ωm; (2) the gate speed descends when the asymmetry of the potential is considered. 相似文献
14.
Exact solution and exotic coherent solition structures of the (2+1)—dimensional generalized nonlinear Schroedinger equation 下载免费PDF全文
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
15.
In this work we study the quantum system with the symmetric Konwent potential and show how to find its exact solutions. We find that the solutions are given by the confluent Heun function. The eigenvalues have to be calculated numerically because series expansion method does not work due to the variable z ≥ 1. The properties of the wave functions depending on the potential parameter A are illustrated for given potential parameters V_0 and a. The wave functions are shrunk towards the origin with the increasing |A|. In particular, the amplitude of wave function of the second excited state moves towards the origin when the positive parameter A decreases. We notice that the energy levels ε_i increase with the increasing potential parameter |A| ≥ 1, but the variation of the energy levels becomes complicated for |A| ∈(0, 1), which possesses a double well. It is seen that the energy levels ε_i increase with |A| for the parameter interval A ∈(-1, 0), while they decrease with |A| for the parameter interval A ∈(0, 1). 相似文献
16.
DING Xiang-Mao WANG Gui-Dong WANG Shi-Kun 《理论物理通讯》2007,47(1):69-77
Motivated by the recently discovered hidden symmetry of the type IIB Green-Schwarz superstring on certain background, the non-semisimple Kac-Moody twisted superalgebra gl(2|2)(2)k is investigated by means of the vector coherent state method and boson-fermion realization. The free field realization of the twisted current superalgebra at general level k is constructed. The corresponding Conformai Field Theory (CFT) has zero central charge. According to the classification theory, this CFT is a nonunitary field theory. After projecting out a U(1) factor and an outer automorphism operator, we get the free field representation of psl(2|2)(2)k, which is the a/gebra of gl(2|2)(2)k modulo the Z4-outer automorphism, the CFT has central charge -2. 相似文献
17.
18.
P. F. Yu J. G. Cai J. M. Liu G. T. Shen 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,44(1):151-158
We investigate the phase decoherence effects on
the entanglement of a two-qubit anisotropic Heisenberg
model
with a nonuniform magnetic field in the x–z-plane. As a
measure of the entanglement, the concurrence of the system is
calculated. It is shown that when the magnetic field is along the
z-axis, the nonuniform and uniform components of the field have
no influence on the entanglement for the cases of
and
, respectively. But when
the magnetic field is not along the z-axis, both the uniform and
the nonuniform components of the field will introduce the
decoherence effects. It is found that the effects of the
Heisenberg chain's anisotropy in the Z-direction on the
entanglement are dependent on the direction of the field.
Moreover, the larger the initial concurrence is, the higher value
it will exhibit during the time evolution of the system for a
proper set of the parameters ν, Δ, θ, γ
, B and b. 相似文献
19.
Generation of unconventional geometric phase gates in ion trap-optical cavity system by squeezed operators 下载免费PDF全文
Based on squeezed operators this paper has implemented an ideal
unconventional geometric quantum gate (GQG) in ion trap-optical
cavity system by radiating the trapped ions with the cavity field of
frequency wc and an external laser field of frequency
wL. It can ensure that the gate time is shorter than
the coherence time for qubits and the decay time of the optical
cavity by appropriately tuning the ionic transition frequency
w0, the frequencies of the cavity mode wc and
the vibrational mode ν. It has also realized the unconventional
GQG under the influence of the cavity decay based on the
squeezed-like operators and found that the present scheme works well
for the smaller cavity decay by investigating the corresponding
fidelity and success probability. 相似文献
20.
H.-Y. Fan Y.-L. Yang 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,39(1):107-113
For an asymmetric beam-splitter a new kind of entangled state
is introduced, we then derive the integration
measure with which such states can make up a complete and orthonormal
representation in two-mode Fock space. We then show how to use
in finding new squeezing operator and new
squeezed state, whose generation can relies on the asymmetric beamsplitter. 相似文献