Figure 1

Push-pull pumping of a hypothetical alkali-metal atom, with nuclear spin quantum number $I=1/2$. In the left panel, atoms are hit by an LCP pulse at a time when the electron spin is $⟨S_z⟩=-1/2$ for the superposition state $|\psi ⟩$ of Eq. (1), and for the end state $|fm⟩=|1,-1⟩$. Neither state can absorb photons from the pulse (dashed lines), but the photons are absorbed strongly by atoms in the other end state $|1,1⟩$ (solid line). In the right panel, the atoms are hit by an RCP pulse half a cycle later, at a time when the electron spin is $⟨S_z⟩=1/2$ for the superposition state $|\psi ⟩$ and for the end state $|1,1⟩$. Neither state can absorb photons from the pulse, but the photons are absorbed strongly by atoms in the other end state $|1,-1⟩$.Reuse & Permissions

Figure 2

Apparatus used to test push-pull pumping. A ${}^{87}\mathrm{R}\mathrm{b}$ cell was placed into a temperature-stabilized oven. Three sets of Helmholtz coils produced a field $B$ of about 2 Gauss in the direction of the probing beam. A monochromatic laser beam was amplitude-modulated (AM) at the 0-0 resonance frequency ${\nu }_{00}={\omega }_{00}/2\pi =6.84\mathrm{G}\mathrm{H}z$ by driving a Mach-Zehnder intensity modulator with microwaves at the frequency ${\nu }_{00}/2$. The sideband structure of the modulated light was monitored with a Fabry-Perot spectrum analyzer. The AM light was converted to light with alternating circular polarization using a Michelson interferometer (shown to the left of the oven).Reuse & Permissions

Figure 3

Enhancement of the 0-0 CPT resonance with push-pull pumping. The top panel shows the conventional CPT signal (the intensity of the light recorded by the photodetector of Fig. 2) for amplitude-modulated light of fixed circular polarization. The CPT contrast obtained with push-pull pumping in the bottom panel is larger by a factor of about 77. The off-resonant signal amplitude is larger for the conventional signal (top panel) because a large fraction of the atoms are pumped into an end state [19]. Push-pull pumping produces no off-resonant polarization so the off-resonant transmission of the vapor is lower. The “contrast” is the increase of the resonant photodetector signal divided by the off-resonance signal. The inset shows the sideband spectrum of the amplitude-modulated light exiting the intensity modulator of Fig. 2.Reuse & Permissions

Figure 4

CPT signal contrasts versus the pumping rate for push-pull and conventional pumping in low-pressure cells. The uncertainty of the theoretical curves, represented by the shaded area, is due to the uncertainty of the relaxation parameters. The insets show the modeled population distributions.Reuse & Permissions