Research ArticlePHYSICS

Demonstration of slow light in rubidium vapor using single photons from a trapped ion

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Science Advances  04 Oct 2019:
Vol. 5, no. 10, eaav4651
DOI: 10.1126/sciadv.aav4651


  • Fig. 1 Absorption, refractive index, and group velocity within a warm 87Rb vapor.

    (A) Absorption profile of the 87Rb D2 line using 780 nm obtained via QFC from a 493-nm laser light with the cell at room temperature. The pump laser’s mode-hop-free tuning range limits the frequency tuning range. The refractive index (B) and group velocity (C) in the vicinity of the two absorption peaks as a function of detuning from peak transmission, δ, at 373 K (blue) and 423 K (red). DFG, difference frequency generation.

  • Fig. 2 Experimental schematic of photon production from a 138Ba+ ion, QFC, and photonic slowing in a warm neutral 87Rb vapor.

    (A) The energy levels of 138Ba+ and schematic showing the ion confined in a segmented blade trap. A TTL pulse-activated AOM controls a 650-nm excitation light. (B) The QFC setup including a PPLN waveguide. Converted light, ω0, is at the difference frequency between photons emitted from the ion at ωion and pump photons at ωpump. The output of the PPLN is fiber coupled to a polarization maintaining single-mode fiber (PM-SMF). A series of filters and a Bragg grating filter out pump light and unconverted 493-nm light, which reduces the amount of anti-Stokes noise. (C) A 87Rb energy level diagram and a vapor cell housed inside a heater through which converted single photons pass. (D) Photons are detected on an APD, and a TCSPC collects the arrival time of the photons with respect to the TTL sent to the AOM. As an example, single-photon temporal shapes at 493 nm (blue circles) and frequency-converted photons after passing through the cell at room temperature (red circles) are shown.

  • Fig. 3 SNR measured after filtering of the frequency-converted ion signal.

    The orange curve is the SNR given the measured conversion efficiencies and noise at each pump power. Inset: Measured conversion efficiency (black) and measured noise counts (red) on the APD as a function of pump power. The black curve is a theoretical fit to the efficiency data, and the red curve is an empirical fit to the noise.

  • Fig. 4 Area-normalized temporal photon shapes.

    Area-normalized temporal shapes of frequency-converted photons that have passed through a warm 87Rb vapor cell. The 87Rb vapor cell temperature is set to the values indicated. The optical density (OD) of the warm vapor is stated for each temperature, at a frequency ω0, and using the same atomic density, N, used to fit the delay curve in Fig. 5.

  • Fig. 5 Delay of the frequency-converted photons emitted from the trapped Ba+ ion after passing through a 87Rb vapor cell as a function of the cell’s temperature.

    The dashed theory curve is a scaled version of Eq. 3 to account for N. The temperature and delay error bars are due to temperature fluctuations over the course of the experiment and the bin width of the histogram photon arrival time data, respectively. Inset: Overlap of temporal shapes of photons transmitted through a 296-K room temperature cell (green circles) and a 395-K cell (red circles). The relative delay between the two traces has been removed to allow for comparison.

  • Fig. 6 Experimental pulse sequence.

    The experimental pulse sequence showing the timing of the laser beams used to state prepare, extract a single photon, and Doppler cool the ion. The parts of the sequence contained in the gray shading are repeated 10,000 times before an extended cooling cycle is performed.

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