Abstract

We show that every Gaussian mixed quantum state can be disentangled by conjugation with a passive symplectic transformation, that is a metaplectic operator associated with a symplectic rotation. The main tools we use are the Werner–Wolf condition on covariance matrices and the symplectic covariance of Weyl quantization. Our result therefore complements a recent study by Lami, Serafini, and Adesso.

Highlights

  • Gaussian states are important for quantum information processing

  • Advances in the study of their entanglement properties is useful and of interest to the community working in the area of continuous variable systems which typically get realized in quantum optics

  • While it is well-known that such states can be made separable (“disentangled”) by diagonalizing the covariance matrix by a symplectic transformation (Williamson normal form), we prove a much stronger result, namely that this disentanglement can.be made by using a symplectic rotation

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Summary

Introduction

Advances in the study of their entanglement properties is useful and of interest to the community working in the area of continuous variable systems which typically get realized in quantum optics. While it is well-known that such states can be made separable (“disentangled”) by diagonalizing the covariance matrix by a symplectic transformation (Williamson normal form), we prove a much stronger result, namely that this disentanglement can.be made by using a symplectic rotation (or “passive symplectic transformation”, to use the physicists’ jargon). We begin by proving the result for bipartite states (Theorem 4), the multipartite readily follows (Corollary 6 ). Theorem 4 has been announced in a Note aux Comptes Rendus de l’Académie des Sciences de Paris [12]

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Separability and entanglement
The covariance matrix of a Gaussian bipartite state
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Symplectic rotations
A simple example
Statement and proof
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Multipartite Gaussian states

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