Electrical Readout for Coherent Phenomena Involving Rydberg Atoms in Thermal Vapor Cells

We present a very sensitive and scalable method to measure the population of highly excited Rydberg states in a thermal vapor cell of rubidium atoms. We detect the Rydberg ionization current in a 5 mm electrically contacted cell. The measured current is found to be in qualitatively good agreement with a theory for the Rydberg population based on a master equation for the three-level problem, including an ionization channel and the full Doppler distributions at the corresponding temperatures. The signal-to-noise ratio of the current detection is substantially better than that of purely optical techniques.

Figure 1

(a) Three-level excitation scheme. The probe beam of Rabi frequency ${\Omega }_p$ couples the states $\mid 1⟩$ and $\mid 2⟩$, while the control laser of Rabi frequency ${\Omega }_c$ couples the states $\mid 2⟩$ and $\mid 3⟩$. (b) Experimental setup. The excitation takes place inside a glass cell filled with Rb vapor. Rydberg ions are detected as a current between two electrodes held at a slightly different electric potential $V$. The electrodes consist of 5 nm thin metallic layers of Ni which provide a 75% transparency for the excitation lasers.

Figure 2

Stark maps of the $42S$ Rydberg state. Transmission of (a) the probe field and (b) the ionization signal, measured simultaneously, after background subtraction. The inset shows an enlarged area at a low electric field. (c) Averaged optical signal measured with a lock-in amplifier and (d) the corresponding single-shot ionization signal recorded 9000 times faster.

Figure 3

Scaling of the measured ionization signal with ground state density for two different probe laser intensities $I=0.8I_{\mathrm{sat}}$ and $30.5I_{\mathrm{sat}}$. The applied voltage is 0.75 V. The error bars represent $\pm 1$ standard deviation confident intervals.

Figure 4

Measured ionization signal as a function of the peak probe field Rabi frequency ${\Omega }_p$ (a) at a fixed coupling Rabi frequency ${\Omega }_c=0.45\times 2\pi \mathrm{MHz}$ and (b) at a coupling laser peak Rabi frequency ${\Omega }_c$ at ${\Omega }_p=14\times 2\pi \mathrm{MHz}$ for different ground state atom densities. The dashed lines are theoretically calculated Rydberg state populations scaled to the corresponding atomic density. The error bars represent $\pm 1$ standard deviation confident intervals.