The PHC criterion and the realignment criterion for pure states in infinite-dimensional bipartite quantum systems are given. Furthermore, several equivalent conditions for pure states to be separable are generalized to infinite-dimensional systems.
In this paper, we present the necessary and sufficient conditions of separability for bipartite pure states in infinite dimensional Hilbert spaces. Let M be the matrix of the amplitudes of ∣ψ⟩, we prove M is a compact operator. We also prove ∣ψ⟩ is separable if and only if M is a bounded linear operator with rank 1, that is the image of M is a one dimensional Hilbert space. So we have related the separability for bipartite pure states in infinite dimensional Hilbert spaces to an important class of bounded linear operators in Functional analysis which has many interesting properties.
In this paper, the realignment criterion and the RCCN criterion of separability for states in infinite-dimensional bipartite quantum systems are established. Let HA and HB be complex Hilbert spaces with dimHA⊗HB=+∞. Let ρ be a state on HA⊗HB and {δk} be the Schmidt coefficients of ρ as a vector in the Hilbert space C2(HA)⊗C2(HB). We introduce the realignment operation ρR and the computable cross norm ∥ρ∥CCN of ρ and show that, if ρ is separable, then ∥ρR∥Tr=∥ρ∥CCN=k∑δk≤1. In particular, if ρ is a pure state, then ρ is separable if and only if ∥ρR∥Tr=∥ρ∥CCN=k∑δk=1.
The positive partial transposition (PPT) criterion and the realignment criterion constitute two of the most important criteria for detecting entanglement. The general- ized partial transposition (GPT) criterion which contains the PPT criterion and the realignment criterion as special cases, provides a necessary condition for a multipartite state to be separable. Here we extend the GPT criterion to the infinite- dimensional multipartite (bipartite) case and show that it includes multipartite (bipartite) PPT criterion and multipartite (bipartite) realignment criterion as special cases as well.