High Resolution Atomic Coherent Control via Spectral Phase Manipulation of an Optical Frequency Comb

We demonstrate high resolution coherent control of cold atomic rubidium utilizing spectral phase manipulation of a femtosecond optical frequency comb. Transient coherent accumulation is directly manifested by the enhancement of signal amplitude and spectral resolution via the pulse number. The combination of frequency comb technology and spectral phase manipulation enables coherent control techniques to enter a new regime with natural linewidth resolution.

Figure 1

(a) Simplified energy level diagram of the three relevant atomic states and frequency domain representation of the chirped comb. $\delta$ is the detuning of the intermediate state from half the two-photon transition frequency. (b) Timing diagram used in the experiments.

Figure 2

The on-resonance $5D_{5/2}$ $F=4$ fluorescence signal is measured (squares) at a field strength of $E_o={10}^7\mathrm{V}/\mathrm{m}$ vs the number of pulses. The solid (dashed) line is the theoretically predicted excited state populations under experimental (asymptotically low) field strengths. The inset shows the quadratic scaling for the first 15 pulses.

Figure 3

The $5D_{5/2}$ $F=4$ line shape is measured (symbols) vs the number of applied femtosecond pulses (10, 15, 20, 80 pulses) with the corresponding FWHM linewidth in the legend. The Lorenztian linewidth of 2.2 MHz after 80 pulses is the asymptotic power-broadened linewidth.

Figure 4

The $5D_{5/2}$ $F=4$ excited state fluorescence is measured (squares) under steady-state excitation ($>100\mathrm{\text{pulses}}$) vs the applied linear frequency chirp. The solid line indicates the steady-state theory and the dashed line is the single-pulse theory. Inset: the signal (symbols) vs pulse number for two values of equal and opposite chirp; the solid and dashed lines are theoretical predictions.

Figure 5

Measured fluorescence (squares) and theoretical prediction (solid line) for the case of destructive quantum interference vs linear frequency chirp. The inset shows two of the many two-photon resonant comb mode pairs symmetrically detuned from the intermediate $5P_{3/2}$ $F=3$ resonance; the closest pair is $\pm 50\mathrm{MHz}$ ($\pm f_r/2$) detuned.