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Periodic Report Summary - INTERACT1DBOSON (Strongly interacting 1D bose gases)

The main objective of project on 'Strongly interacting 1D gases' was to realise one-dimensional systems of interacting particles using ultracold atoms confined in optical potentials. The fundamental idea is to take advantage from the possibility to tune and change the dimensionality and the effect of interaction in an ensemble of cold atoms manipulated by means of optical potentials with a very high degree of control on the physical parameters.

In particular the proposal was to trap a Bose-Einstein condensate of 87Rb in a red detuned two-dimensional optical lattice. When the two perpendicular optical lattices are tightly confining the atoms along their direction of propagation, an array of one-dimensional (1D) systems can be obtained. In fact, the atoms can effectively move only along the direction where no lattice is present.

Furthermore, the interactions are affected by the reduced dimensionality of the system and are expected to produce (if strong enough) very peculiar effects. In the original project, we were also proposing to add a blue detuned dipole optical trap to change the confinement of the atomic samples along the longitudinal direction. This would change the linear density of the 1D systems independently from their transverse confinement giving the possibility to change in an independent way the effect of interactions.

1D systems realised using samples of ultracold atoms manipulated by light, offers the possibility to monitor and characterise physical properties that are not simply accessible in other 1D systems as quantum-wires, carbon nanotubes, spin chains and spin ladders.

More precisely, in the project we were proposing to use inelastic light scattering (Bragg spectroscopy) to study the excitation spectrum of this system and the noise correlation technique as a way to monitor the spatial correlations extensions.

In the project, we were also mentioning the willing to study metal-insulator quantum-phase transitions in these 1D systems induced by the presence of a longitudinal periodic or disordered potential. In the first case (periodic potential along the 1D atomic system), one can drive the superfluid to Mott insulator transition, while adding a disorder potential the Bose glass phase should be observable.

During the project we have realised and studied arrays of 1D bosons loading a Bose-Einstein condensate of 87Rb in a two-dimensional (2D) optical lattice. The lattice potential is strongly enough that the coupling between the 1D atomic systems can be completely neglected in the time scale of our experiment and an array of independent 1D system is obtained. A systematic characterisation of the phase properties of this system has been performed both using Bragg spectroscopy and the analysis of time of flight density distribution.

Also the superfluid to Mott insulator transition has been explored in these systems adding a longitudinal optical lattice with adjustable intensity. The crossover from the two superfluid to the inhomogeneous Mott insulator phase has been characterised using Bragg spectroscopy that allows to transfer an excitation to the system with full control on the energy and the momentum of the excitation.

We have also started to add to our system a blue detuned dipole trap which will allow us to control the linear density of the 1D Bose gases approaching the regime were strong interaction will induce a 'fermionisation' of the sample. In this regime, called Tonks-Girardeau regime, repulsive interactions in a bosonic system mimic what the Pauli exclusion principle produces in a sample of identical fermions.

Concerning the study of disorder induced phenomena, due to the fact that the project has been terminated in advanced, we did not attack yet this part.