Quantum memory of a squeezed vacuum for arbitrary frequency sidebands

We have developed a quantum memory that is completely compatible with current quantum information processing for continuous variables of light, where arbitrary frequency sidebands of a squeezed vacuum can be stored and retrieved using bichromatic electromagnetic induced transparency. The 2 MHz sidebands of squeezed vacuum pulses with temporal widths of 470 ns and a squeezing level of $-1.78\pm 0.02$ dB were stored for 3 $\mu$s in laser-cooled ${}^{87}\mathrm{Rb}$ atoms. Squeezing of $-0.44\pm 0.02$ dB, which is the highest squeezing reported for a retrieved pulse, was achieved.

Figure 1

Three-level atoms coupled to two-mode probe light and bichromatic control light.

Figure 2

Schematic diagram of the experimental setup. BS: beam splitter, HBS: half-beam splitter, AOM: acousto-optic modulator, PD: photodetector, PZT: piezo electric transducer, Amp: RF amplifier.

Figure 3

Quadrature noise spectra of the squeezed vacuum incident together with the monochromatic control light, where the frequencies of the control light were (a) resonant on the $5\hspace{0.5em}{}^2{S}_{1/2},F=2\to 5\hspace{0.5em}{}^2{P}_{1/2},F^{\prime }=2$ transition, (b) detuned by 500 kHz, and (c) detuned by 2 MHz. (d), (e), and (f) show the numerical simulations of the EIT for the squeezed vacuum shown in (a), (b), and (c), respectively. Traces A, B, C, D, and E are described in the text.

Figure 4

Quadrature noise spectra of the squeezed vacuum incident with bichromatic control light detuned by $\pm 2$ MHz obtained by (a) squaring the Fourier transform of the direct homodyne signals and by (b) multiplying the 2-MHz sine waves having phases that are identical to the phase of the beating amplitude of the control light and (c) the phase that differs from the beating amplitude of the control light by $\pi /2$ before taking the Fourier transform. Traces A, B, C, D, and E are identical to those in Fig. 3.

Figure 5

Temporal variation of the quadrature noises of mode ${\mathrm{â}}_{+}$ (left column) and mode ${\mathrm{â}}_{-}$ (right column), where the relative phases between the squeezed vacuum and the LO were set to $\pi /2$ [(a) and (b)] and $0$ [(c) and (d)]. Traces A, B, C, and D are described in the text.