### Abstract

We explore the statistical behaviour of the discrete nonlinear Schrodinger equation as a test bed for the observation of negative-temperature (i.e. above infinite temperature) states in Bose-Einstein condensates in optical lattices and arrays of optical waveguides. By monitoring the microcanonical temperature, we show that there exists a parameter region where the system evolves towards a state characterized by a finite density of discrete breathers and a negative temperature. Such a state persists over very long (astronomical) times since the convergence to equilibrium becomes increasingly slower as a consequence of a coarsening process. We also discuss two possible mechanisms for the generation of negative-temperature states in experimental setups, namely, the introduction of boundary dissipations and the free expansion of wavepackets initially in equilibrium at a positive temperature.

Original language | English |
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Article number | 023032 |

Number of pages | 13 |

Journal | New Journal of Physics |

Volume | 15 |

DOIs | |

Publication status | Published - 19 Feb 2013 |

### Keywords

- Bose-Einstein condensation
- statistical-mechanics
- optical lattice
- gases
- solitons
- systems
- arrays

### Cite this

*New Journal of Physics*,

*15*, [023032]. https://doi.org/10.1088/1367-2630/15/2/023032