Electromagnetically Induced Transparency in Cesium Vapor with Probe Pulses on the Single-Photon Level

We perform electromagnetically induced transparency (EIT) experiments in cesium vapor with pulses on the single-photon level for the first time. This was made possible by an extremely large total suppression of the EIT coupling beam by 118 dB mainly due to a newly developed triple-pass planar Fabry-Pérot etalon filter. Slowing and shaping of single-photon light pulses as well as the generation of pulses suitable for quantum key distribution applications and testing of approaches for single photon storage is demonstrated. Our results extend single-photon EIT to the particularly interesting wavelength of the Cs $D1$ line.

Figure 1

(a) Experimental setup consisting of probe and coupling laser, frequency modulation spectroscopy setup (FMS), an electro-optical modulator (EOM), Wollaston prism (WP), polarization optics, i.e., half-wave plate (HWP), quarter-wave plate (QWP), and polarizing beam splitter, as well as a Glan-Thompson prism (GT) and spectral filtering (see text). A photodiode (PD) and avalanche photodiode (APD) are used for detection. (b) $\Lambda$-type atomic level scheme implemented in Cs. $E_p$ is the probe field, $E_c$ is the coupling field. (c) Details of the multipass Fabry-Pérot etalon used for spectral filtering of the coupling beam. Two retroreflectors above and below the etalon direct the light beam at different positions three times through the instrument. The substrates are connected by three piezoelements, and a closed-loop controller together with strain gauge sensors in each piezoelement controls the mirror distance.

Figure 2

Scan of the FP filter around the probe transition wavelength (black points). The simulation [gray (red) line] is performed using a Voigt profile with the FP linewidth as FWHM for the Lorenzian part; the Gaussian FWHM as fit parameter is found to be 47 MHz.

Figure 3

(a) Delayed single-photon probe pulse. The black [gray (blue)] line shows the pulse without (with) EIT cell. For comparison the curve for the delayed pulse is multiplied by a factor of 4 and plotted as thick gray (red) curve. (b) Dependence of time delays on the FWHM spectral and temporal width of the probe pulse. The vertical bar indicates the width of the EIT transmission window. The dots are experimental results, and the solid line is a theoretical calculation (see text).

Figure 4

Control of a single-photon wave packet by modulation of the coupling laser. The black curve is the undisturbed pulse without EIT cell. The lower gray (blue) curve shows the probe pulse which is split coherently into two components thus forming a time-bin encoded state on the single-photon level. For comparison the curve for the split pulse is multiplied by a factor of 5.5 and plotted as thick gray (red) curve.