Quantum Phase Transitions with Parity-Symmetry Breaking and Hysteresis.
Symmetry-breaking quantum phase transitions play a key role in several condensed matter, cosmology and nuclear physics theoretical models1-3. 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 is made of an ultra-cold 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 temperature4, the investigation of macroscopic quantum tunneling of the order parameter in the hysteretic regime and the production of strongly quantum entangled states at critical points5.
Istituto Nazionale di Ottica-CNR, 50019 Sesto Fiorentino, Italy.
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Trenkwalder
LENS European Laboratory for Nonlinear Spectroscopy, and Dipartimento di Fisica e Astronomia, Università di Firenze, 50019 Sesto Fiorentino, Italy.
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Spagnolli
LENS European Laboratory for Nonlinear Spectroscopy, and Dipartimento di Fisica e Astronomia, Università di Firenze, 50019 Sesto Fiorentino, Italy.
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Semeghini
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.
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Coop
Istituto Nazionale di Ottica-CNR, 50019 Sesto Fiorentino, Italy.
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Landini
Istituto Nazionale di Ottica-CNR, 50019 Sesto Fiorentino, Italy; Instituto de Física de São Carlos, Universidade de São Paulo, C.P. 369, 13560-970, São Carlos, São Paulo, Brazil.
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Castilho
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; Quantum Science and Technology in Arcetri, QSTAR, 50125 Firenze, Italy.
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Pezzè
LENS European Laboratory for Nonlinear Spectroscopy, and Dipartimento di Fisica e Astronomia, Università di Firenze, 50019 Sesto Fiorentino, Italy.
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Modugno
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.
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Inguscio
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; Quantum Science and Technology in Arcetri, QSTAR, 50125 Firenze, Italy.
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Smerzi
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.
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Fattori