Cooling atoms with a moving one-way barrier

We implement and demonstrate the effectiveness of a cooling scheme using a moving, all-optical, one-way barrier to cool a sample of ${}^{87}\mathrm{Rb}$ atoms, achieving nearly a factor of 2 reduction in temperature. The one-way barrier, composed of two focused, Gaussian laser beams, allows atoms incident on one side to transmit, while reflecting atoms incident on the other. The one-way barrier is adiabatically swept through a sample of atoms contained in a far-off-resonant, single-beam, optical dipole trap that forms a nearly harmonic trapping potential. As the barrier moves longitudinally through the potential, atoms become trapped to one side of the barrier with reduced kinetic energy. The adiabatic translation of the barrier leaves the atoms at the bottom of the trapping potential, only minimally increasing their kinetic energy.

Figure 1

Schematic representation of the one-way barrier cooling process for atoms trapped in a harmonic potential. The atoms pass through the barrier from left to right and become trapped near their turning points, then reduce their potential energy by following the barrier to the bottom of the potential.

Figure 2

Optical setup showing the dipole trap, barrier beams, imaging system, and translation stage.

Figure 3

Dipole-trap translation and imaging sequence. The times shown correspond to a translation speed of $5\hspace{0.5em}\mathrm{mm}/\mathrm{s}$.

Figure 4

Spatial distributions of atoms in the dipole trap with (black curves) and without (gray curves) the one-way barrier. The barrier beams are located at the plot center. Each curve is an average of $16$ repetitions of the experiment, smoothed slightly for clarity.

Figure 5

The width of the atomic distribution in the dipole trap as function of time, measured from the start of the sweep, with (squares) and without (circles) the one-way barrier. The vertical line indicates the time when the sweep has finished. Each data point is an average of $16$ repetitions of the experiment, with the standard deviation as the error.

Figure 6

The width of the atomic distribution after passing through the barrier, as function of translation velocity. Square points represent data taken while the translation stage was coming to rest at $1.5\hspace{0.5em}\mathrm{mm}$, while circular points represent data taken as the stage passed $1.5\hspace{0.5em}\mathrm{mm}$ at constant velocity. Each square (circular) data point represents an average of $16$ ($6$) repetitions of the experiment.