Effect of Förster resonances on the excitation statistics of many-body Rydberg systems

We provide evidence for the dipole blockade of Rydberg excitation by examining the distributions of the number of Rydberg excitations created in ensembles of interacting Rydberg atoms. We show that, over a range of densities, the Rydberg excitation number distributions become significantly narrower when an applied electric field is used to tune the ${}^{85}\mathrm{Rb}$ interaction channel $45D_{5∕2}+45D_{5∕2}\to 43F+47P_{3∕2}$ into Förster resonance. Substantially sub-Poissonian distributions that agree with published theory were achieved using very dense atom samples tuned into Förster resonance.

Figure 1

(Color online) Illustration of an ensemble of atoms in an optical dipole trap. A blockade causes the excitation volume to break up into “excitation domains,” or regions inside of which there is, ideally, one Rydberg excitation.

Figure 2

(Color online) State-selective field-ionization spectra for excitation into $45D_{5∕2}$ states in the absence of an applied field (upper curve) and with an applied Förster-resonant field (lower curve). The regions enclosed in circles exhibit a very weak free-electron signal. The smooth curve shows the time-dependence of the field-ionization pulse (right axis).

Figure 3

(Color online) Probability distribution histogram of the number of detected $45D_{5∕2}$ Rydberg excitations, $N$. For comparison, a Poisson distribution with equal mean and area is plotted as a solid line.

Figure 4

(Color online) Average detected $Q$ value for excitation in the absence of an applied electric field and a field $E_{\mathrm{F}}$ for three densities: $\rho =5\times {10}^{11}{\mathrm{cm}}^{-3}$ (squares), $\rho =2\times {10}^{11}{\mathrm{cm}}^{-3}$ (circles), and $\rho =1\times {10}^{11}{\mathrm{cm}}^{-3}$ (triangles).

Figure 5

(Color online) Number of detected Rydberg excitations, $N$, as a function of the peak intensity of the $5P_{3∕2}\to 45D_{5∕2}$ laser. The circles represent excitation in zero field, and the squares represent excitation in a field $E_{\mathrm{F}}$. The inset shows Rydberg excitation spectra for $5\mathrm{W}∕{\mathrm{cm}}^2$ (dashed line) and $60\mathrm{W}∕{\mathrm{cm}}^2$ (solid line) for field $E=E_{\mathrm{F}}$.