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1.
A potential scheme is proposed for generating cluster states of many
atoms in cavity quantum electradynamics (QED), in which an unorthodox
encoding is employed with the ground state being qubit $\left\vert
0\right\rangle $ while two closely spaced upper states being qubit
$\left\vert 1\right\rangle $. Throughout the scheme the cavities can
be in thermal states but are only virtually excited. We show how to
create the cluster states by performing a two-step but no
single-qubit operation. Discussion is also carried out on the
experimental feasibility of our scheme. 相似文献
2.
Entanglement evolution in an anisotropic two-qubit Heisenberg XYZ model with Dzyaloshinskii-Moriya interaction 下载免费PDF全文
This paper investigates the entanglement evolution of a two-qubit anisotropic Heisenberg XYZ chain in the presence of Dzyaloshinskii-Moriya interaction.The time evolution of the concurrence is studied for the initial pure entangled states cos θ |00 + sin θ |11 and cos |01 + sin |10 at zero temperature.The influences of Dzyaloshinskii-Moriya interaction D,anisotropic parameter and environment coupling strength γ on entanglement evolution are analysed in detail.It is found that the effect of noisy environment obviously suppresses the entanglement evolution,and the Dzyaloshinskii-Moriya interaction D acts on the time evolution of entanglement only when the initial state is cos |01 + sin |10.Finally,a formula of steady state concurrence is obtained,and it is shown that the stable concurrence,which is independent of different initial states and Dzyaloshinskii-Moriya interaction D,depends on the anisotropic parameter and the environment coupling strength γ. 相似文献
3.
Generation of atomic Greenberger-Horne-Zeilinger states and cluster states through cavity-assisted interaction 下载免费PDF全文
This paper proposes a scalable scheme to generate n-atom GHZ states and cluster states by using the basic building block, i.e., a weak coherent optical pulse [α) being reflected successively from a single-atom cavity. In the schemes, coherent state of light is used instead of single photon source, homodyne measurement on coherent light is done kastead of single photon detection, and no need for individually addressing keeps the schemes easy to implement from the experimental point of view. The successful probabilities of our protocols approach unity in the ideal case. 相似文献
4.
我们研究一个耦合2谐振子系统的本征态问题。我们构造了由算子(x1+p2)和(x2+p1)的共同本征态组成的新纠缠态表象︱γ>。在︱γ>表象得到了系统哈密顿的本征值和本征态。同样的问题用二次量子化表象进行了研究。我们发现在Fock空间,二次量子化表象可以被用来推得本征态的正规积表示。特别是发现了系统基态为广义2模压缩态 相似文献
5.
Unifying the theory of integration within normal-, Weyl- and antinormal-ordering of operators and the s-ordered operator expansion formula of density operators 下载免费PDF全文
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
6.
P. Kok 《Optics and Spectroscopy》2011,111(4):520-522
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.
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
8.
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
9.
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
10.
Three-party quantum secret sharing of secure direct communication based on χ-type entangled states 下载免费PDF全文
Based on χ-type entangled states and the two-step protocol [Deng F G,Long G L and Liu X S 2003 Phys.Rev.A 68 042317],a quantum secret sharing protocol of secure direct communication based on χ-type entangled states |χ00 3214 is proposed.Using some interesting entanglement properties of this state,the agent entirety can directly obtain the secret message from the message sender only if they collaborate together.The security of the scheme is also discussed. 相似文献
11.
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
12.
The mixedness of the N-qubit quantum states with exchange symmetry has been studied, and the results show that the linear entropy of the single qubit reduced density matrix (RDM), which can describe the mixedness, is completely determined by the expectation values 〈Sz〉 and 〈S±〉 for both the pure and the mixed states. The mixedness of the pure states can be used to describe the bipartite entanglement, as an example we have calculated the mixedness of the Dicke state and the spin squeezed Kitagawa-Ueda state. For the mixed states, we determine the mixedness properties of both the ground states and the thermal states in mean-field clusters of spin-1/2 particles interacting via the anisotropy Heisenberg XXZ interaction, and found for the ferromagnetic case (J 〈 0), the mixedness will approximate to the pairwise entanglement when the anisotropic parameter △ 〉 △c. 相似文献
13.
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
14.
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
15.
Improvement of the short-term stability of atomic fountain clock with state preparation by two-laser optical pumping 下载免费PDF全文
《中国物理 B》2021,30(5):50602-050602
To improve the signal to noise ratio(SNR) and the short-term stability of cesium atomic fountain clocks, the work of two-laser optical pumping is presented theoretically and experimentally. The short-term stability of the NIM6 fountain clock has been improved by preparing more cold atoms in the |F = 4, mF= 0〉 clock state with a shortened cycle time.Two π-polarized laser beams overlapped in the horizontal plane have been applied after launching, one is resonant with|F = 4〉→ |F = 4〉 transition and the other is resonant with |F = 3〉→ |F = 4〉 transition. With optical pumping, the population accumulated in the |mF= 0〉 clock state is improved from 11% to 63%, and the detection signal is increased by a factor of 4.2, the SNR of the clock transition probability and the short-term stability are also improved accordingly. 相似文献
16.
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
17.
18.
A generalized Collins formula derived by virtue of the displacement-squeezing related squeezed coherent state representation 下载免费PDF全文
Based on the displacement-squeezing related squeezed
coherent state representation ≤ft\vert z\right\rangle _{g} and
using the technique of integration within an ordered product of
operators, this paper finds a generalized Fresnel operator, whose
matrix element in the coordinate representation leads to a
generalized Collins formula (Huygens--Fresnel integration
transformation describing optical diffraction). The generalized
Fresnel operator is
derived by a quantum mechanical mapping from z to sz-rz^{\ast } in the %
≤ft\vert z\right\rangle _{g} representation, while ≤ft\vert
z\right\rangle _{g} in phase space is graphically denoted by an
ellipse. 相似文献
19.
O. Jedrkiewicz R. Loudon J. Jeffers 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,39(1):129-140
Previous work on the retrodictive theory of direct
detection is extended to cover the homodyne detection of coherent optical
signal states
and
. The retrodictive input state probabilities are obtained by
the application of Bayes' theorem to the corresponding predictive
distributions, based on the probability operator measure (POM) elements for
the homodyne process. Results are derived for the retrodictive information
on the complex amplitude of the signal field obtainable from the difference
photocount statistics of both 4-port and 8-port balanced homodyne detection
schemes. The local oscillator is usually assumed much stronger than the
signal but the case of equal strengths in 4-port detection is also
considered. The calculated probability distributions and error rates are
illustrated numerically for values of signal and local oscillator strengths
that extend from the classical to the quantum regimes. 相似文献
20.
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