# Project B8:

Quantum phase transitions with cold polar molecules

## Summary

The central goal of this project is to study ground state properties and quantum phase transitions of ultra-cold polar molecules driven by external fields into in the strongly interacting regime. The trapping and cooling of polar molecules is currently a field of high experimental interest with the ultimate goal of creating quantum degenerate molecules in the rotational and vibrational ground state. A characteristic property of these heteronuclear molecules is a finite permanent electric dipole moment, which allows for driving an anisotropic dipole-dipole interaction between the particles using static electric fields and/or microwave fields. This strong and tuneable long-range interaction is an ultimate tool for driving quantum degenerate systems of polar molecules into the interaction-dominated regime and offers the opportunity of wide-ranged applications in designing strongly correlated systems. The main focus in this project is on two aspects: first, the determination of ground state properties in a setup close to the current experimental situation. Here, the important questions concern the realization of phases which naturally suppress inelastic collisions and allow for the preparation of a long lived many-body systems of polar molecules at low temperatures. Secondly, subjecting the polar molecules to an additional optical lattice allows for the realization of extended Hubbard models. The tools available to control and tune the interaction potential between the polar molecules will be used to derive interesting Hamiltonians from the microscopic theory with the goal to design quantum simulators for strongly correlated quantum phases. These quantum simulators offer a way to gain an understanding on complex and so-far puzzling systems of matter. Especially it opens up a way to search for topological and exotic phases.

## Project leaders

Prof. Dr. Hans Peter Büchler, Institut für Theoretische Physik III, Universität Stuttgart

## Refs & Publications

M. Klinsmann, D. Peter, and H. P. Büchler*"Ferroelectric quantum phase transition with cold polar molecules"*

*New J. Phys.,*; arXiv:1412.0521 [cond-mat.quant-gas]

**17**, 085002 (2015)*;*doi: 10.1088/1367-2630/17/8/085002

N. Lang and H. P. Büchler

*"Topological states in a microscopic model of interacting fermions"*

*Phys. Rev. B,*; arxiv:1504.04233

**92**, 041118(R) (2015)*;*doi: 10.1103/PhysRevB.92.041118

N. Lang and H. P. Büchler

*"Exploring quantum phases by driven dissipation"*

*Phys. Rev. A,*; arxiv:1408.4616

**92**, 012128 (2015)*;*doi: 10.1103/PhysRevA.92.012128

D. Peter, N. Y. Yao, N. Lang, S. D. Huber, M. D. Lukin, and H. P. Büchler

*"Topological bands with Chern number C = 2 by dipolar exchange interactions"*

*Phys. Rev. A,*; arxiv:1410.5667 [cond-mat.quant-gas]

**91**, 053617 (2015)*;*doi: 10.1103/PhysRevA.91.053617

A. Bühler, N. Lang , C. V. Kraus, G. Möller, S. D. Huber, and H. P. Büchler

*"Majorana modes and p-wave superfluids for fermionic atoms in optical lattices"*

*Nature Communications,*; arxiv:1403.0593 [cond-mat.quant-gas]

**5**, 4504 (2014)*;*doi: 10.1038/ncomms5504

W. Lechner, H. P. Büchler, and P. Zoller

*"The Role of Quantum Fluctuations in the Hexatic Phase of Cold Polar Molecules"*

*Phys. Rev. Lett.,*; arXiv:1401.5682 [cond-mat.stat-mech]

**112**, 255301 (2014)*;*doi: 10.1103/PhysRevLett.112.255301

D. Peter, A. Griesmaier, T. Pfau, and H. P. Büchler

*"Driving dipolar fermions into the quantum Hall regime by spin-flip induced insertion of angular momentum"*

Phys. Rev. Lett.

**110**, 145303 (2013);

*arXiv:1302.1308 [cond-mat.quant-gas]*;

**(editor**

D. Peter, S. Müller, S. Wessel, and H. P. Büchler

S. D. Huber and H. P. Büchler

L. Bonnes and S. Wessel

A. Bühler and H. P. Büchler

L. Bonnes and S. Wessel

L. Bonnes and S. Wessel

L. Bonnes and S. Wessel

L. Bonnes, H. P. Büchler, and S. Wessel

L. Pollet, J.D. Picon, H. P. Büchler, and M. Troyer

D. Peter, S. Müller, S. Wessel, and H. P. Büchler

*"Anomalous Behavior of Spin Systems with Dipolar Interactions"**Phys. Rev. Lett.***109**, 025303 (2012)*;*doi: 10.1103/PhysRevLett.109.025303S. D. Huber and H. P. Büchler

*"Dipole-Interaction-Mediated Laser Cooling of Polar Molecules to Ultracold Temperatures"**Phys. Rev. Lett.***108**, 193006 (2012)*;*doi: 10.1103/PhysRevLett.108.193006L. Bonnes and S. Wessel

*"Half-vortex unbinding and Ising transition in constrained superfluids"**Phys. Rev. B***85**, 094513 (2012)*;*doi: 10.1103/PhysRevB.85.094513A. Bühler and H. P. Büchler

*"Supersolid phase in atomic gases with magnetic dipole interaction"**Phys. Rev. A***84**, 023607 (2011)*;*doi: 10.1103/PhysRevA.84.023607L. Bonnes and S. Wessel

*"Generic first-order vs. continuous quantum nucleation of supersolidity"**Phys. Rev. B***84**, 054510 (2011)*;*doi: 10.1103/PhysRevB.84.054510L. Bonnes and S. Wessel

*"Pair Superfluidity of Three-Body Constrained Bosons in Two Dimensions"**Phys. Rev. Lett.***106**, 185302 (2011)*;*doi: 10.1103/PhysRevLett.106.185302L. Bonnes and S. Wessel

*"Supersolid polar molecules beyond pairwise interactions"**Phys. Rev. B***83**, 134511 (2011)*;*doi: 10.1103/PhysRevB.83.134511L. Bonnes, H. P. Büchler, and S. Wessel

*"Polar molecules with three-body interactions on the Honeycomb lattice"**New J. Phys.***12**, 053027 (2010)L. Pollet, J.D. Picon, H. P. Büchler, and M. Troyer

*"Supersolid phase with cold polar molecules on a triangular lattice"**Phys. Rev. Lett.***104**, 125302 (2010)