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

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.