By using thermo field dynamics, we studied the phase transitions of thermal squeezed states. Two critical points are obtained in certain cases. They correspond to the transitions from thermal squeezed state to pure squeezed state and to thermal state respectively.
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.
Abstract By making use of thermo field dynamics(TFD),higher order fluctuations and higher order squeezing of quadrature components for coherent states and squeezed states with thermal noise have been studied.The higher order fluctuations of the phase for these thermalized states have been investigated using the concept of measured phase operators.Thus the dependence of the lower and higher order fluctuations and squeezing on temperature in these states at finite temperature can be seen.It is significant to discuss the effect of temperature on the fluctuations and squeezing,since the states of real field are always at finite temperatures.
By making use of thermo-field dynamics(TFD),higher-order fluctuations and higher-order squeezing of quadrature components for coherent states and squeezed states with thermal noise have been studied.The higher-order fluctuations of the phase for these thermalized states have been investigated using the concept of measured phase operators.Thus the dependence of the lower-and higher-order fluctuations and squeezing on temperature in these states at finite temperature can be seen.It is significant to discuss the effect of temperature on the fluctuations and squeezing,since the states of real field are always at finite temperatures.
Much attention has been given in the past to two classes of squeezed states: the squeezed vacuum and coherent states. Here we study the effects of squeezing on number states and on thermal field states. The statistical properties of these various squeezed states are discussed using the second-order correlation functions. The quasiprobabilities of the Wigner, Q, and positive P representations are calculated and compared for the squeezed states. The Glauber P representation for the squeezed thermal state explicitly shows the limit of its applicability. The photon number distributions of the squeezed number and squeezed thermal states are extensively discussed and new interference effects in phase space are shown to lead to highly structured number distributions.