Superfluidity of Flexible Chains of Polar Molecules

We study quantum chains formed in a gas of polar bosonic molecules confined in a stack of N identical one- and two-dimensional optical lattice layers, with molecular dipole moments aligned perpendicularly to the layers. Quantum Monte Carlo simulations of a single chain reveal its quantum roughening transition. The case of finite in-layer density of molecules is analyzed within the J-current model approximation, and it is found that N-layered molecular superfluid phase can undergo a quantum phase transition to a rough chain superfluid. A theorem is proven that no superfluidity of chains with length shorter than N is possible. The scheme for detecting the chain formation is proposed.