We study by means of first principle Quantum Monte Carlo simulations the ground state phase diagram of a system of dipolar bosons with aligned dipole moments, and with the inclusion of a two-body repulsive potential of varying range. The system is shown to display a supersolid phase in a relatively broad region of the phase diagram, featuring different crystalline patterns depending on the density and on the range of the repulsive part of the interaction (scattering length). The supersolid phase is sandwiched between a classical crystal of parallel filaments and a homogeneous superfluid phase. We show that a "roton" minimum appears in the elementary excitation spectrum of the superfluid as the system approaches crystallization. The predictions of this study are in quantitative agreement with recent experimental results.

We use the Maximum Entropy Method (MaxEnt) to estimate the dynamic structure factor of superfluid 4 He at T = 1 K, by inverting imaginary-time density correlation functions computed by Quantum Monte Carlo (QMC) simulation. Our procedure consists of a Metropolis random walk in the space of all possible spectral images, sampled from a probability density which includes the entropic prior, in the context of the so-called "classic" MaxEnt. Comparison with recent work by other authors shows that, contrary to what is often stated, sharp features in the reconstructed image are not "washed out" by the entropic prior if the underlying QMC data have sufficient precision. Only spurious features that tend to appear in a straightforward χ 2 minimization are suppressed. arXiv:1808.08663v5 [cond-mat.stat-mech]

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We study by quantum Monte Carlo simulations the low-temperature phase diagram of dipolar bosons confined to one dimension, with dipole moments aligned along the direction of particle motion. A hard core repulsive potential of varying range (σ) is added to the dipolar interactio n, in order to ensure stability of the system against collapse. In the σ → 0 limit the physics of the system is dominated by the potential energy and the ground state is quasi-crystalline; as σ is increased the attractive part of the interaction weakens and the equilibrium phase evolves from quasi-crystalline to a non-superfluid liquid. At a critical value σc, the kinetic energy becomes dominant and the system undergoes a quantum phase transition from a self-bound liquid to a gas. In the gaseous phase with σ → σc, at low density attractive interactions bring the system into a "weak" superfluid regime. However, gas-liquid coexistence also occurs, as a result of which the topologically protected superfluid regime is not approached. arXiv:1911.05216v2 [cond-mat.stat-mech]

We present a comprehensive theoretical study of the phase diagram of a system of many Bose particles interacting with a two-body central potential of the so-called Lennard-Jones form. First-principles path-integral computations are carried out, providing essentially exact numerical results on the thermodynamic properties. The theoretical model used here provides a realistic and remarkably general framework for describing simple Bose systems ranging from crystals to normal fluids to superfluids and gases. The interplay between particle interactions on the one hand and quantum indistinguishability and delocalization on the other hand is characterized by a single quantumness parameter, which can be tuned to engineer and explore different regimes. Taking advantage of the rare combination of the versatility of the many-body Hamiltonian and the possibility for exact computations, we systematically investigate the phases of the systems as a function of pressure (P) and temperature (T), as well as the quantumness parameter. We show how the topology of the phase diagram evolves from the known case of 4He, as the system is made more (and less) quantum, and compare our predictions with available results from mean-field theory. Possible realization and observation of the phases and physical regimes predicted here are discussed in various experimental systems, including hypothetical muonic matter.