Storage and retrieval of a squeezed vacuum was successfully demonstrated using electromagnetically induced transparency. The squeezed vacuum pulse having a temporal width of 930 ns was incident on the laser cooled 87Rb atoms with an intense control light in a coherent state. When the squeezed vacuum pulse was slowed and spatially compressed in the cold atoms, the control light was switched off. After 3 mus of storage, the control light was switched on again, and the squeezed vacuum was retrieved, as was confirmed using the time-domain homodyne method.

We report generation of a continuous-wave squeezed vacuum resonant on the Rb D 1 line (795 nm) using periodically poled KTiOPO 4 (PPKTP) crystals. With a frequency doubler and an optical parametric oscillator based on PPKTP crystals, we observed a squeezing level of −2.75 ± 0.14dB and an anti-squeezing level of +7.00 ± 0.13dB. This system could be utilized for demonstrating storage and retrieval of the squeezed vacuum, which is important for the ultra-precise measurement of atomic spins as well as quantum information processing. c 2018 Optical Society of America OCIS codes: 000.0000, 999.9999.Recently, a novel scheme for mapping the quantum state of a light field onto an atomic ensemble was proposed 1 in which the electromagnetically induced transparency plays a major role. This "storage of light" technique enables us to overcome the difficulty of localizing photons which are mainly used as carriers of quantum information. While the storage and retrieval of a single photon state has already been realized, 2, 3 it has not been demonstrated for a squeezed vacuum. It should be noted that the former experiment can be performed conditionally whereas the latter should be demonstrated in deterministic manner and is thus sensitive to field loss. Mapping the squeezed state onto an atomic ensemble is a critical task not only for quantum information processing but also for ultra-precise measurement of atomic spins.To perform such an experiment, it is necessary to generate a high-level squeezed vacuum resonant on an atomic transition. By utilizing KNbO 3 crystals, a squeezed vacuum has already been generated resonant on the Cs D-lines (852 nm, 894 nm) and the interaction between the atoms and the squeezed vacuum has also been investigated intensively.4 However, there have been relatively few experiments done on the generation of a squeezed vacuum resonant on the Rb D-lines (780 nm, 795 nm), while Rb has played an important role in quantum information processing along with Cs. So far experiments have been limited to -0.9 dB squeezing with quasiphase-matched MgO:LiNbO 3 waveguides 5 and -0.85 dB squeezing with the self-rotation of Rb itself.6 Note that the KNbO 3 crystal which is useful at the Cs resonance line cannot be utilized at the Rb one. 7 In this letter we demonstrate -2.75 dB squeezing at 795 nm using a periodically-poled KTiOPO 4 (PPKTP) crystal, 7, 8 which to the best of our knowledge, is the highest squeezing obtained at the Rb D 1 line. Figure 1 shows the experimental setup. A continuouswave Ti:Sapphire laser (Coherent, MBR 110) at 795 nm was employed in this experiment. The beam from the Ti:Sapphire laser was phase-modulated by an electrooptic modulator (EOM). This modulation was utilized to lock a cavity for frequency doubling and a cavity for squeezing using the FM sideband method.9 The frequency doubler had a bow-tie type ring configuration with two spherical mirrors (radius of curvature of 100 mm) and two flat mirrors. One of the flat mirrors (PT1) had a reflectivity of 90% at 795 nm and was used as the inpu...

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 87Rb 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 micros was observed for the probe pulse having a temporal width of 10 micros.

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