Quantum phase transitions with parity-symmetry breaking and hysteresis

Year: 2016

Authors: Trenkwalder A., Spagnolli G., Semeghini G., Coop S., Landini M., Castilho P., Pezzè L., Modugno G., Inguscio M., Smerzi A., Fattori M.

Autors Affiliation: Istituto Nazionale di Ottica-CNR, 50019 Sesto Fiorentino, Italy;
LENS European Laboratory for Nonlinear Spectroscopy, and Dipartimento di Fisica e Astronomia, Università di Firenze, 50019 Sesto Fiorentino, Italy;
ICFO-Institut de Ciencies Fotoniques, Barcelona Institute of Science and Technology, 08860 Castelldefels (Barcelona), Spain;
Instituto de Física de São Carlos, Universidade de São Paulo, C.P. 369, 13560-970 São Carlos, São Paulo, Brazil
Quantum Science and Technology in Arcetri, QSTAR, 50125 Firenze, Italy

Abstract: Symmetry-breaking quantum phase transitions play a key role in several condensed matter, cosmology and nuclear physics theoretical models(1-3). Its observation in real systems is often hampered by finite temperatures and limited control of the system parameters. In this work we report, for the first time, the experimental observation of the full quantum phase diagram across a transition where the spatial parity symmetry is broken. Our system consists of an ultracold gas with tunable attractive interactions trapped in a spatially symmetric double-well potential. At a critical value of the interaction strength, we observe a continuous quantum phase transition where the gas spontaneously localizes in one well or the other, thus breaking the underlying symmetry of the system. Furthermore, we show the robustness of the asymmetric state against controlled energy mismatch between the two wells. This is the result of hysteresis associated with an additional discontinuous quantum phase transition that we fully characterize. Our results pave the way to the study of quantum critical phenomena at finite temperature(4), the investigation of macroscopic quantum tunnelling of the order parameter in the hysteretic regime and the production of strongly quantum entangled states at critical points(5).

Journal/Review: NATURE PHYSICS

Volume: 12 (9)      Pages from: 826  to: 829

More Information: We thank our colleagues of the Ultracold Quantum Gases group in Florence for constant support. We acknowledge discussions with G. Jona-Lasinio and C. Presilla. This work has been supported by ERC Starting grant AISENS, INFN (Firb RBFR08H058_001, Micra) and by EU-FP7 (QIBEC). S.C. acknowledges support from the Erasmus Mundus Doctorate Program Europhotonics (Grant No. 159224-1-2009-FR-ERA MUNDUS-EMJD) and P.C. acknowledges support from the CNPq agency of the Brazilian Ministry of Science, Technology and Innovation.
KeyWords: Bose-Einstein condensate; double-well; gas
DOI: 10.1038/nphys3743

Citations: 92
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