### Abstract

The authors use the formalism of thermo field dynamics and the classical Cramer's theorem to show that if two quantum systems are prepared independently and their centre of mass is found to be a thermal squeezed state, then both systems were prepared in thermal squeezed states. This constitutes an alternative derivation of the quantum version of Cramer's theorem. Further, they consider the case of two systems that are prepared independently and their centre of mass is in a pure state in the expanded space of thermo field dynamics. In this case it is shown that the system is also separable in the centre of mass and relative coordinates, and again all the states involved are thermal squeezed states.

Original language | English |
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Article number | 016 |

Pages (from-to) | 4527-4533 |

Number of pages | 7 |

Journal | Journal of Physics A: Mathematical and General |

Volume | 24 |

Issue number | 19 |

DOIs | |

Publication status | Published - 1991 |

Externally published | Yes |

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### ASJC Scopus subject areas

- Statistical and Nonlinear Physics
- Physics and Astronomy(all)
- Mathematical Physics

### Cite this

*Journal of Physics A: Mathematical and General*,

*24*(19), 4527-4533. [016]. https://doi.org/10.1088/0305-4470/24/19/016