Quantum multicritical points (QMCPs) emerge at the junction of two or more quantum phase transitions due to interplay disparate fluctuations, leading novel universality classes. While critical have been well characterized, our understanding QMCPs is much limited, even though they might be less elusive study experimentally than points. Here, we characterize QMCP an interacting heterogeneous syst...

We study entanglement and spin squeezing in the ground state of three qubits interacting via the transverse Ising model. We give analytical results for the entanglement and spin squeezing, and a quantitative relation between the concurrence, quantifying the entanglement of two spins, and the spin squeezing parameter, measuring the degree of squeezing. Finally, by appropriately choosing the exch...

We propose an effective transverse Ising model (TIM) as a means to treat both metallic and hightemperature superconductivity. The model is inspired by features which are present in the GorterCasimir two-fluid model of superconductivity, but it encompasses also the formalism used to treat the phase transitions in hydrogen-bonded ferroelectrics. We treat the model in the random-phase approximatio...

Convergent expansions of the wavefunctions for the ground state and low-lying excited states of quantum transverse Ising systems are obtained. These expansions are employed to prove that the dispersion relation for a single quasi-particle has a convergent expansion.