THE MIXED COHERENT STATE REPRESENTATION OF THE DENSITY OPERATOR IN THERMO-FIELD DYNAMICS

2007 ◽  
Vol 21 (04) ◽  
pp. 183-188 ◽  
Author(s):  
H.-Y. FAN ◽  
H.-L. LU
Keyword(s):  
Coherent State ◽  
Density Operator ◽  
Master Equations ◽  
Entangled State ◽  
Entangled State Representation ◽  
State Representation ◽  
Thermo Field Dynamics

In the framework of thermo-field dynamics, invented by Umezawa et al., we construct a mixed coherent state representation of density operator ρ. This new representation is useful because it provides an approach to retrieve ρ from its c-number solution of master equations in the entangled state representation.

New Complex Function Space Related to Both Entangled State Representation and Spin Coherent State

2020 ◽  
Vol 26 (1) ◽  
pp. 7-13
Author(s):  
李兰兰 LI Lan-lan ◽  
张科 ZHANG Ke ◽  
余海军 YU Hai-jun ◽  
杜建明 DU Jian-ming ◽  
范洪义 FAN Hong-yi
Keyword(s):  
Coherent State ◽  
Function Space ◽  
Complex Function ◽  
Entangled State ◽  
Entangled State Representation ◽  
State Representation ◽  
Spin Coherent State

OPERATOR-SUM REPRESENTATION OF DENSITY OPERATORS AS SOLUTIONS TO MASTER EQUATIONS OBTAINED VIA THE ENTANGLED STATE APPROACH

2008 ◽  
Vol 22 (25) ◽  
pp. 2435-2468 ◽  
Author(s):  
HONG-YI FAN ◽  
LI-YUN HU
Keyword(s):  
Point Of View ◽  
Master Equations ◽  
Entangled State ◽  
Entangled State Representation ◽  
State Representation ◽  
Partial Trace ◽  
New Approach ◽  
Density Operators ◽  
Phase Sensitive ◽  
System Mode

We solve various master equations to obtain density operators' infinite operator-sum representation via a new approach, i.e., by virtue of the thermo-entangled state representation that has a fictitious mode as a counterpart mode of the system mode. The corresponding Kraus operators from the point of view of quantum channel are derived, whose normalization conditions are proved. Miscellaneous characters possessed by different quantum channels, such as decoherence, phase diffusion, damping, and amplification, can be shown explicitly in the entangled state representation of the density operators. Squeezing transformation is applied to the density operator for decoherence to generate a master equation for describing the phase sensitive process. Partial trace method for deriving new density operators is also introduced. Throughout our discussion, the technique of integration within an ordered product (IWOP) of operators is fully used.

PHASE OPERATOR AND PHASE STATE IN THERMO FIELD DYNAMICS

2009 ◽  
Vol 24 (15) ◽  
pp. 1219-1226 ◽  
Author(s):  
HONG-YI FAN ◽  
NIAN-QUAN JIANG
Keyword(s):  
Coherent States ◽  
Phase State ◽  
Entangled State ◽  
Entangled State Representation ◽  
Phase Operator ◽  
State Representation ◽  
Thermo Field Dynamics ◽  
Limiting Case ◽  
Thermo Entangled State Representation ◽  
Thermo Entangled State

We extend the Susskind–Glogower phase operator and phase state in quantum optics to thermo field dynamics (TFD). Based on the thermo entangled state representation, we introduce thermo excitation and de-excitation operators with which the phase operator and phase state in TFD can be constructed. The phase state treated as a limiting case of a new SU(1, 1) coherent states is also exhibited.

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