Atom slowing via dispersive optical interactions

A promising technique of atom slowing is proposed. It is based upon the dispersive interaction of atoms with optical potential pulses generated by a far-off-resonance standing wave modulated in time. Each pulse reduces the velocity by a small amount. By repeating the process thousands of times, the velocity can be lowered from several hundreds of meters per second down to almost zero, over a path as short as $20\mathrm{c}\mathrm{m}$. In the absence of any random recoil process, the initial characteristics of the beam are preserved.

Figure 1

Calculated trajectories of the wave-packet center when comoving potential pulses of different durations ${\tau }_1$ are present. Parameters used in this simulation are such that a negative refraction is realized (see text): magnetic field 500 G, initial velocity, $2\mathrm{m}/\mathrm{s}$, spatial period, $\Lambda =5\mathrm{m}\mathrm{m}$ and $\tau =0.37\mathrm{m}\mathrm{s}$. At time ${\tau }_1$, both position and velocity are continuous.

Figure 2

Scheme of the comoving optical potential slower. A far-off-resonance, linearly polarized standing wave ($\lambda =811.5\mathrm{n}\mathrm{m}$) is produced by a separated-arm interferometer. Light intensity is modulated in time by a signal $S\left(t\right)$ (see text). The atom beam is introduced with a small inclination through holes drilled in the mirrors.

Figure 3

Evolution of the velocity $v$ and the statistical velocity width $\Delta v_{\mathrm{stat}}$ (see text) multiplied by 100 as a function of the total number $N$ of comoving optical potential pulses. The total length needed to reach the quasizero velocity (for $N=2\times {10}^6$) is $19.3\mathrm{c}\mathrm{m}$. The laser intensity is $32\mathrm{m}\mathrm{W}/\mathrm{m}{\mathrm{m}}^2$ and the detuning is $3.45\mathrm{G}\mathrm{Hz}$.

Figure 4

(Upper part) Evolution of the spatial width $\delta x$ of the wave packet as a function of time. Upper curve: Free evolution (no potential); lower curve: the potential is present. The initial width [$\delta x_0\left(0\right)=0.635\mathrm{n}\mathrm{m}$] corresponds to a relative dispersion $\delta k/k=0.2\%$ in the momentum space. (Lower part) Evolution (in ${\log }_{10}$ scale) as a function of time of densities in phase space $(k,x)$, defined as ${\rho }_{{\mathrm{ps}}_0}={\left(\delta k\delta x_0\right)}^{-1}$ for free propagation and ${\rho }_{\mathrm{ps}}={\left(\delta k\delta x\right)}^{-1}$ when the potential is present. Note that ${\rho }_{{\mathrm{ps}}_0}$ corresponds as well to the separable free coordinates $y$ and $z$.