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Journal of Modern Optics

Four-mode coherent entangled state as an entanglement of two bipartite coherent entangled states

Liyun Hu, Hong-Yi Fan

Published Apr 10, 2008• 4 citations
Publisher

Abstract

By introducing a four-mode unitary operator U = exp[−iλ(X 1 P 2 + X 2 P 3 + X 3 P 4 + X 4 P 1)], we show how a four-mode coherent entangled state can be generated by entangling a two bipartite coherent entangled state. The corresponding squeezed vacuum state U|0000⟩ in four-mode Fock space is derived by virtue of the technique of integration within ordered production of operators, which exhibits the standard squeezing for the four-mode quadratures. A new ideal quantum mechanical representation |α, β, γ⟩ is constructed from U|0000⟩ in the limit of infinite squeezing, which possesses the properties of both coherent and entangled states. The entanglement involved in |α, β, γ⟩ is explained. A scheme for generating |α, β, γ⟩ is presented.

DOI
10.1080/09500340701606986

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We show that the operator $U=\mathrm{exp}[\ensuremath{-}{ir(Q}_{1}{P}_{2}{+Q}_{2}{P}_{3}{+Q}_{3}{P}_{1})]$ is a three-mode squeezing operator for the three-mode quadratures exhibiting the standard squeezing, the corresponding squeezed vacuum state in three-mode Fock space is derived by virtue of the technique of integration within ordered product of operators. The entanglement involved in such a state is explained. The optical network for producing the three-mode squeezed state is proposed.
A new kind of four-mode continuous variable coherent-entangled state is proposed in the Fock space by using the technique of integration within an ordered product, which exhibits both the properties of a coherent state and an entangled state, and spans a complete and orthonormal representation. The conjugate state of the four-mode continuous variable coherent-entangled state is derived by using the Fourier transformation. Moreover, a simple experimental protocol of generating a four-mode continuous variable coherent-entangled state is proposed by using beam splitters. As applications of this four-mode continuous variable coherent-entangled state, a four-mode entangled state and a four-mode squeezing-Fresnel operator are constructed.
The new two mode coherent entangled state representation 1p,β〉 is proposed by the technique of integration within an ordered product of operators. Its characteristics and mechanism are analysed. The results show that, the common eigenvector |p,β〉 of p1-p2 and a1+a2 exhibits both the characteristics of the coherent state and entangled state. The 1|p,β〉 makes up a new quantum mechanical representation and possesses the completeness relation. The ideal single-mode squeezed state |p=0〉2=exp［1/2a+22|0〉2 and the vacuum state |0〉1 overlapping on a beam splitter may produce the coherent entangled state |p,β〉at the output by the modulation of the laser field.
We show that the best way to study the relationship between quantum entanglement and quantum squeezing for the multimode case is through constructing the new n -pair entangled state representation . The explicit form of the 2 n -mode squeezing operator which squeezes the n -pair entangled state can be directly derived via the transition from to where M is an n × n complex matrix, and the technique of integration within an ordered product of operators. We also analyze the squeezing properties of the 2 n -mode squeezed state for M being Hermitian, and obtain the variances of the 2 n -mode quadrature operators in the 2 n -mode squeezed vacuum state with a concise result; the condition for reaching the minimum of the uncertainty relationship is also investigated.