Ultraslow Propagation of Squeezed Vacuum Pulses with Electromagnetically Induced Transparency

We have succeeded in observing ultraslow propagation of squeezed vacuum pulses with electromagnetically induced transparency. Squeezed vacuum pulses (probe lights) were incident on a laser-cooled ${}^{87}\mathrm{Rb}$ gas together with an intense coherent light (control light). A homodyne method sensitive to the vacuum state was employed for detecting the probe pulse passing through the gas. A delay of $3.1\mu \mathrm{s}$ was observed for the probe pulse having a temporal width of $10\mu \mathrm{s}$.

Figure 1

Schematic diagram of the experimental setup. BS: beam splitter, AOM: acousto-optic modulator, PD: photodetector, SA: spectrum analyzer, Amp.: rf amplifier, PZT: piezoelectric transducer. AOM5 consists of two AOMs to cancel the frequency shift due to the diffraction. AOM6 also consists of two AOMs, where, rather than the first-order beam, the zeroth-order beam was used.

Figure 2

(a) Dependence of the transmission of the coherent probe light on two-photon detuning. (b) Quadrature noise of the probe light in the squeezed state that passed through the EIT medium. ● (■) indicate the quadrature noises when the relative phase between the LO and the squeezed vacuum was set to $\theta =0$ ($\pi /2$).

Figure 3

(A) Balanced homodyne signals of the probe light with (a) a monochromatic LO and (b) a bichromatic LO. (B) Shot noise level. We normalized the quadrature noise levels using the shot noise.

Figure 4

Time dependence of the measured noise of the probe pulse with the relative phase (a) $\theta =\pi /2$ and (b) $\theta =0$ and (c) that of the photon flux derived from data (a) and (b). Trace (A) shows the quadrature noises of the squeezed vacuum pulses in the absence of the control lights and the cold atoms. Trace (B) shows the quadrature noises of the squeezed vacuum pulses incident on the cold atoms without the control light. Trace (C) indicates the shot noises. Traces (D), (E), and (F) show the quadrature noises of the squeezed vacuum pulses incident on the cold atoms with control lights of intensities 200, 100, and $50\mu \mathrm{W}$, respectively.