Low-temperature excitations within the Bethe approximation

@article{Biazzo2013LowtemperatureEW,
  title={Low-temperature excitations within the Bethe approximation},
  author={Indaco Biazzo and Abolfazl Ramezanpour},
  journal={Journal of Statistical Mechanics: Theory and Experiment},
  year={2013},
  volume={2013},
  pages={04011}
}
We propose the variational quantum cavity method to construct a minimal energy subspace of wavevectors that are used to obtain some upper bounds for the energy cost of the low-temperature excitations. Given a trial wavefunction we use the cavity method of statistical physics to estimate the Hamiltonian expectation and to find the optimal variational parameters in the subspace of wavevectors orthogonal to the lower-energy wavefunctions. To this end, we write the overlap between two wavefunctions… 
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