Macroscopic Quantum States and Quantum Phase Transition in Dicke Models of Arbitrary Atom-Number
The energy spectrum of Dicke Hamiltonians with and without the rotating wave approximation for arbitrary atom-number is obtained analytically with the variational method, in which the effective pseudo-spin Hamiltonian resulted from the expectation value in the boson-field coherent state is diagonali...
| Main Authors: | , , |
|---|---|
| Format: | Text |
| Language: | unknown |
| Published: |
arXiv
2011
|
| Subjects: | |
| Online Access: | https://dx.doi.org/10.48550/arxiv.1110.3862 https://arxiv.org/abs/1110.3862 |
| Summary: | The energy spectrum of Dicke Hamiltonians with and without the rotating wave approximation for arbitrary atom-number is obtained analytically with the variational method, in which the effective pseudo-spin Hamiltonian resulted from the expectation value in the boson-field coherent state is diagonalized by the spin-coherent-state transformation. In addition to the ground-state energy an excited macroscopic quantum-state is found corresponding to the south-and-north-pole gauges of the spin-coherent states respectively. Our results of ground-state energies in exact agreement with various approaches show that these models exhibit a zero-temperature quantum phase transition of second-order for any number of atoms, which however was commonly considered as a phenomenon of the thermodynamic limit with the atom-number tending to infinite. The critical behavior of geometric phase is analyzed, which displays no singularity at the critical point. : 5 pages, 2 figures |
|---|