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We consider a model of bosons on a regular lattice with a kinetic energy due to hopping among sites and a potential energy due to strong on site interaction. A superfluid phase is expected when the ground state of the local energy is doubly degenerate. We consider a new scheme of simmetry breaking associated to the superfluid phase in which the order parameter is the statistical average of the quantum coherence operator associated to the superposition of the degenerate local ground states. In the strong coupling limit a systematic expansion of the free energy can be performed in terms of the hopping amplitude at constant order parameter. Within such an expansion we obtain a self-consistent equation for the order parameter. The first order approximation gives, in the case of degeneracy between single occupied and empty state, the same result of the standard mean field approximation for the ``hard core bosons. This new approach to the superfluid phase is shown to have a natural application to the implementation of quantum computation on a superfluid.
Non-locality is a fundamental trait of quantum many-body systems, both at the level of pure states, as well as at the level of mixed states. Due to non-locality, mixed states of any two subsystems are correlated in a stronger way than what can be acc
This paper represents the full version of a paper published earlier in Physica A [246 (1997), 275]. The present paper includes argumentation, proofs and details omitted in the shortened version. The papers are a further development of the approach in
Formation of quantum scars in many-body systems provides a novel mechanism for enhancing coherence of weakly entangled states. At the same time, coherence of edge modes in certain symmetry protected topological (SPT) phases can persist away from the
There is a long standing problem about how close a connection exists between superfluidity and Bose condensation. Employing recent technology, for the case of confined finite Bose condensed systems in TOP traps, these questions concerning superfluidi
We investigate the emergence of quantum scars in a general ensemble of random Hamiltonians (of which the PXP is a particular realization), that we refer to as quantum local random networks. We find two types of scars, that we call stochastic and stat