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

Abstract

A cold atomic realization of a quantum correlated state of many fermions on a lattice, eg. superfluid, has eluded experimental realization due to the entropy problem. Here we propose a route to realize such a state using holographic lattice and confining potentials. The potentials are designed to produces a band insulating state (low heat capacity) at the trap center, and a metallic state (high heat capacity) at the periphery. The metal “cools” the central band insulator by extracting out the excess entropy. The central band insulator can be turned into a superfluid by tuning an attractive interaction between the fermions. Crucially, the holographic lattice allows the emergent superfluid to have a high transition temperature – even twice that of the effective trap temperature. The scheme provides a promising route to a laboratory realization of a fermionic lattice superfluid, even while being adaptable to simulate other many body states.

Thermodynamics and magnetism in the 2D-3D crossover of the Hubbard model

“…Finally, one can cool and study S with an arbitrary t ⊥ /t this way by applying an optical barrier to turn transport off between S and R, and then adiabatically change V z in the S region to give the desired t ⊥ /t. This cooling method bears similarities to other entropy redistribution protocols [40][41][42][43][83][84][85][86][87][88][89][90][91] but overcomes some difficulties. In particular, schemes that rely on metal reservoirs created by changing the local potential, rather than lattice anisotropy, suffer at large U/t from the fact that the metals created this way are bad metals, therefore they carry significantly less entropy, than, e.g., a non-interacting metal.…”

“…Of particular relevance here is that, although experiments have achieved spin correlations which extend across the finite lattice [40], so far experiments have not reached sufficiently low temperatures or entropies to observe a true long-range ordered AF phase. Theoretical proposals exist, for example, to use spatial subregions as repositories for excess entropy, allowing for lower temperatures in other regions [18,[41][42][43], but reaching the Néel temperature, and below, remains an outstanding challenge.…”

Finite-temperature study of correlations in a bilayer band insulator

“…Recent progress made in the experiments towards the realization of the attractive Hubbard model has been of great interest [2,10]. There have been some theoretical attempts to "increase" the characteristic temperature T c which can be achieved experimentally [11,12]. In this work, we focus on the bilayer attractive Hubbard model band-insulator model discussed in Ref.…”

Cooling quantum gases with entropy localization

“…In discussing 'cooling' of cold atomic systems, the relevant quantity is often entropy rather than temperature [9][10][11][12][13][14][15][16][17][18]. Temperature can be radically reduced by adiabatically changing system parameters [19][20][21][22] (for example the depth of an optical lattice), but, there is no utility in lowering the temperature if the other energy scales in the system are commensurably reduced.…”