Double-Resonance Spectroscopy of Interacting Rydberg-Atom Systems

The energy level spectrum of a many-body system containing two shared, collective Rydberg excitations is measured using cold atoms in an optical dipole trap. Two pairs of independently tunable laser pulses are employed to spectroscopically probe the spectrum in a double-resonance excitation scheme. Depending on the magnitude of an applied electric field, the Rydberg-atom interactions can vary from resonant dipole-dipole to attractive or repulsive van der Waals, leading to characteristic signatures in the measured spectra. Our results agree with theoretical estimates of the magnitude and sign of the interactions.

Figure 1

The left panel shows a shadow image of atoms in an optical dipole trap. The right panel shows an excitation domain [23] with zero, one, or two interacting Rydberg excitations. The nature of the energy-shifted band of states $|2r⟩$ depends on whether the interactions are resonant dipole-dipole or van der Waals in nature. Owing to the interactions, the $|1r⟩\to |2r⟩$ transition energy $W^{\prime }$ differs from the energy of a single Rydberg excitation $W$.

Figure 2

Effect of an applied electric field $E$ on state-mixing collisions for excitation into the states $45D_{5/2}$ (a),(c) and $43D_{5/2}$ (b),(d). (a) and (b) show SSFI signals after 700 ns interaction time for different values of $E$ along with the SSFI electric field pulse. (c) and (d) show the fraction of the total SSFI signal in $47P$ or $45P$ states as a function of $E$.

Figure 3

Experimental timing diagram. (a)–(c) Control voltages applied to the acousto-optic modulators to generate the optical pulses shown in (d) and (e). (f) SSFI pulse.

Figure 4

Spectra for excitation into the $45D_{5/2}$ state: $S_2({\nu }_2)$ (squares; left axes), ${\tilde{S}}_{1+2}({\nu }_2)$ (circles; right axis). (a) shows data with zero applied electric field and 240 averages per point, while (b) shows data with an applied field of $E_F$ and 200 averages per point.

Figure 5

Spectra for excitation into the $43D_{5/2}$ state: $S_2({\nu }_2)$ (squares; left axis) and ${\tilde{S}}_{1+2}({\nu }_2)$ (circles; right axis). (a) shows data with zero applied electric field and 455 averages per point, while (b) shows data with an applied field of $0.15\mathrm{V}/\mathrm{cm}$ and 260 averages per point.