# Bosonic molecules in a lattice: unusual fluid phase from multichannel interactions

## TL;DR

This paper demonstrates that multichannel interactions in ultracold bosonic molecules in optical lattices create an unusual fluid phase with suppressed phase coherence, altering the traditional phase diagram and potentially impacting related systems.

## Contribution

It introduces the concept of a fluid phase induced by multichannel interactions, characterized by suppressed phase coherence despite number fluctuations, and uses multiple methods to analyze the phase diagram.

## Key findings

- Identification of an unusual fluid phase between superfluid and Mott insulator.
- Phase coherence can be arbitrarily suppressed in a two-site system.
- Multichannel interactions are significant even without dipolar interactions.

## Abstract

We show that multichannel interactions significantly alter the phase diagram of ultracold bosonic molecules in an optical lattice. Most prominently, an unusual fluid region intervenes between the conventional superfluid and the Mott insulator. In it, number fluctuations remain but phase coherence is suppressed by a significant factor. This factor can be made arbitrarily large, at least in a two-site configuration. We calculate the phase diagram using complementary methods, including Gutzwiller mean-field and density matrix renormalization group (DMRG) calculations. Although we focus on bosonic molecules without dipolar interactions, we expect multichannel interactions to remain important for dipolar interacting and fermionic molecules.