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Register a new userGround-state properties of a one-dimensional system of dipoles
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A one-dimensional (1D) Bose system with dipole-dipole repulsion is studied at zero temperature by means of a Quantum Monte Carlo method. It is shown that in the limit of small linear density the bosonic system of dipole moments acquires many properties of a system of non-interacting fermions. At larger linear densities a Variational Monte Carlo calculation suggests a crossover from a liquid-like to a solid-like state. The system is superfluid on the liquid-like side of the crossover and is normal in the deep on the solid-like side. Energy and structural functions are presented for a wide range of densities. Possible realizations of the model are 1D Bose atom systems with permanent dipoles or dipoles induced by static field or resonance radiation, or indirect excitons in coupled quantum wires, etc. We propose parameters of a possible experiment and discuss manifestations of the zero-temperature quantum crossover.
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A quantum Monte Carlo simulation of a system of hard rods in one dimension is presented and discussed. The calculation is exact since the analytical form of the wavefunction is known, and is in excellent agreement with predictions obtained from asymptotic expansions valid at large distances. The analysis of the static structure factor and the pair distribution function indicates that a solid-like and a gas-like phases exist at high and low densities, respectively. The one-body density matrix decays following a power-law at large distances and produces a divergence in the low density momentum distribution at k=0 which can be identified as a quasi-condensate.
We introduce Gutzwiller conjugate gradient minimization (GCGM) theory, an ab initio quantum many-body theory for computing the ground-state properties of infinite systems. GCGM uses the Gutzwiller wave function but does not use the commonly adopted Gutzwiller approximation (GA), which is a major source of inaccuracy. Instead, the theory uses an approximation that is based on the occupation probability of the on-site configurations, rather than approximations that decouple the site-site correlations as used in the GA. We test the theory in the one-dimensional and two-dimensional Hubbard models at various electron densities and find that GCGM reproduces energies and double occupancies in reasonable agreement with benchmark data at a very small computational cost.
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The competition between the tendency of magnetic moments to order at low temperatures, and the tendency of conduction electrons to shield these moments, can result in a phase transition that takes place at zero Kelvin, the quantum critical point (QCP). So far, the ground state of these types of systems has remained unresolved. We present neutron scattering experiments that show that the ground state of a sample representative of a class of QCP-systems is determined by the residual interactions between the conduction electrons, resulting in a state with incommensurate intermediate-range order. However, long-range order is thwarted by quantum fluctuations that locally destroy magnetic moments, leaving the system with too few moments to achieve long-range order.
We propose to utilize the sub-system fidelity (SSF), defined by comparing a pair of reduced density matrices derived from the degenerate ground states, to identify and/or characterize symmetry protected topological (SPT) states in one-dimensional interacting many-body systems. The SSF tells whether two states are locally indistinguishable (LI) by measurements within a given sub-system. Starting from two polar states (states that could be distinguished on either edge), the other combinations of these states can be mapped onto a Bloch sphere. We prove that a pair of orthogonal states on the equator of the Bloch sphere are LI, independently of whether they are SPT states or cat states (symmetry-preserving states by linear combinations of states that break discrete symmetries). Armed with this theorem, we provide a scheme to construct zero-energy exitations that swap the LI states. We show that the zero mode can be located anywhere for cat states, but is localized near the edge for SPT states. We also show that the SPT states are LI in a finite fraction of the bulk (excluding the two edges), whereas the symmetry-breaking states are distinguishable. This can be used to pinpoint the transition from SPT states to the symmetry-breaking states.
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