Fermionic superfluid from a bilayer band insulator in an optical lattice

Abstract

We propose a model to realize a fermionic superfluid state in an optical lattice circumventing the cooling problem. Our proposal exploits the idea of tuning the interaction in a characteristically low entropy state, a band-insulator in an optical bilayer system, to obtain a superfluid. By performing a detailed analysis of the model including fluctuations and augmented by a variational quantum Monte Carlo calculations of the ground state, we show that the superfluid state obtained has high transition temperature of the order of the hopping energy. Our system is designed to suppress other competing orders such as a charge density wave. We suggest a laboratory realization of this model via an orthogonally shaken optical lattice bilayer.

Supersolid phases of dipolar fermions in a two-dimensional-lattice bilayer array

“…Previous mean field analysis on dipolar fermions placed onto a single-layer square lattice, with arbitrary orientation and considering dipoles with fixed orientation, have predicted the melting among SF and DW phases [20][21][22][23] and a arXiv:1607.08846v2 [cond-mat.quant-gas] 24 Oct 2016 variety of DW phases [24] respectively. Also, an extended model including a mixture of Fermi molecules with contact interactions, loaded in a bilayer array predicted density ordered phases as well as superfluids phases [15,[25][26][27][28]. The possibility of supersolid phases in these dipolar Fermi gases has also been studied [21,22,29].…”

Density redistribution effects in fermionic optical lattices

“…Without an optical lattice evaporative cooling easily reaches temperatures lower then T /T F ≈ 0.08 [5,6], but such low temperatures have not yet been achieved in optical lattices. In principle the process of lattice loading should be performed adiabatically, but in practice one will always do so in a finite time, thus deviating from the completely adiabatic regime and incurring some heating.…”

Cooling a Band Insulator with a Metal: Fermionic Superfluid in a Dimerized Holographic Lattice

“…Notwithstanding the spectacular new developments 5 6 7 8 9 10 11 12 13 , headway in the use of cold atomic systems to study interesting strongly interacting/correlated regimes such as those of the Hubbard model (both repulsive/attractive) has been hampered by the entropy problem 14 . For example, the remarkable progress made in the study of the BCS(Bardeen-Cooper-Schrieffer) to BEC(Bose-Einstein Condensate) of interacting fermions 15 16 (see 17 for an overview), has not been replicated on a lattice in the single band tight binding limit despite many proposals 18 19 20 21 22 23 24 25 (see also 14 , and references therein).…”

“…Having obtained a low entropy band insulating state, we now tune an onsite attractive interaction U of the Hubbard type (using, e.g., a Feshbach resonance 36 37 ) to drive the band insulating state into a superfluid state 25 38 39 40 41 42 43 . The emergent superfluid state can be modeled by the action where stands for the fermion Grassman variable associated with momentum , sublattice flavour α , β = A , B ; σ is the spin label, τ is the imaginary time, N is the number of unit cells of the homogeneous system, and is a 2 × 2 matrix, defined as …”

“…When the saddle point is non-zero, we consider Gaussian fluctuations about it and obtain the collective excitations of the superfluid which govern the transition temperature, owing to the 2D nature of our system. In the following we shall only discuss the final physics, see 25 for details.…”