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Modern Physics Letters A

NEW THERMO EXCITATION STATES AND OPERATIONS IN THERMO FIELD DYNAMICS

Xuefen Xu, Shiqun Zhu

Published Mar 28, 2009• 0 citations
Publisher

Abstract

According to the thermo field dynamics proposed by Takahashi–Umezawa, the Hamiltonian h = a†a - ã†ã and h|n, ñ〉 = 0 of the original optical field excitation state |n〉 and its tilde state |ñ〉 in the Hilbert space cannot embody the eigenvalue spectrum of h. To avoid the weakness, new thermo excitation states are successfully constructed by introducing appropriate thermo excitation operators. It is noted that they are entangled states. Applications of the new thermo excitation state in constructing new thermo squeezed state and phase state are also presented.

DOI
10.1142/s0217732309028321

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According to the thermo field dynamics proposed by Takahashi–Umezawa, the Hamiltonian h = a†a - ã†ã and h|n, ñ〉 = 0 of the original optical field excitation state |n〉 and its tilde state |ñ〉 in the Hilbert space cannot embody the eigenvalue spectrum of h. To avoid the weakness, new thermo excitation states are successfully constructed by introducing appropriate thermo excitation operators. It is noted that they are entangled states. Applications of the new thermo excitation state in constructing new thermo squeezed state and phase state are also presented.
By analyzing the characters of thermo field dynamics, which is proposed by Takahashi and Umezawa, we find that a new physical state, named the thermo-invariant coherent state, should exist in thermal equilibrium. This state not only maintains the whole energy of the system and the reservoir but is also a coherent state. We find its explicit form, its relation to the thermal coherent state and the thermal entangled state. When the whole system is in this state, annihilating a quantum of the system and in the meanwhile annihilating a hole with negative energy in the reservoir will not change the whole energy.