Low-frequency vacuum squeezing via polarization self-rotation in Rb vapor

Abstract

We observed squeezed vacuum light at 795 nm in 87 Rb vapor via resonant polarization self-rotation, and report noise sidebands suppression of ≈ 1 dB below shot noise level spanning from acoustic (30 kHz) to MHz frequencies. This is the first demonstration of sub-MHz quadrature vacuum squeezing in atomic systems. The spectral range of observed squeezing matches well typical bandwidths of electromagnetically induced transparency (EIT) resonances, making this simple technique for generation of optical fields with non-classical statistics at atomic transitions wavelengths attractive for EIT-based quantum information protocols applications. At present optical parametric oscillators (OPO) operating below threshold offer the best performance for squeezed vacuum generation [9]. Many EIT experiments are based on Rb D 1 line (795nm) transitions, and OPO performance is limited at this wavelength due to increased material absorption for 397 nm nearultraviolet up-converted pump field, as well as various photothermal effects arising at higher pump power [10]). Another challenge is to produce low-frequency squeezing to match the characteristic bandwidth of EIT resonances. While the generation of squeezed light with subMHz sideband frequencies is theoretically possible [11], practically it becomes a very challenging and resourceconsuming task due to significant experimental complexity. Nevertheless, impressive progress in generation of low-frequency squeezed vacuum at Rb resonance wavelength has been recently reported [10], and such sources were used to demonstrate slow light and reversible mapping of squeezed vacuum states via EIT in Rb [12,13,14].

Polarization squeezing of light by single passage through an atomic vapor

“…2 as a function of the laser frequency around the F = 1 → F ′ = 1, 2 and F = 2 → F ′ = 1, 2 transitions. The results are consistent with previous observations [15,17] where only the minimum and maximum noise levels at a given laser frequency were reported. The largest squeezing occurs around the F = 2 → F ′ = 1, 2 transitions.…”

“…Our experiments are closely related to previous observations of squeezing via PSR [14,15,17]. In order to detect the quadrature dependent squeezing, these experiments utilize a homodyne detection setup in which the field been analyzed is made to interfere with a local oscillator.…”

“…However, RIS can also occur between orthogonal polarization components of a single light beam. In such case, the field is said to be polarization squeezed [8,9] and the noise reduction is described in terms of squeezing of the fluctuations of one of the Stokes operators:Here a x , a y are the field destruction operators for the orthogonal linear polarizations x and y. Polarization squeezing has been produced via propagation in optical fibers [10,11], through the combination on a polarizing beam splitter of two quadrature squeezed light beams [12] and through the interaction of linearly polarized light with cold atoms inside an optical cavity [9,13].It has been recently demonstrated that the single passage of a linearly polarized pump beam through a few-cmlong atomic vapor cell results in squeezing of the polarization orthogonal to that of the pump (vacuum squeezing) [14][15][16][17] as a consequence of the nonlinear optics mechanism known as polarization self-rotation (PSR) [18][19][20]. Vacuum squeezing via PSR has been observed for the D1 [15][16][17] and D2 [14] transitions using 87 Rb vapor.…”

“…Vacuum squeezing via PSR has been observed for the D1 [15][16][17] and D2 [14] transitions using 87 Rb vapor. As noted in [9], the existence of polarization squeezing can be inferred from these results.…”

Squeezing bandwidth controllable twin beam light and phase sensitive nonlinear interferometer based on atomic ensembles

“…Up to now, many groups have successfully generated low frequency squeezing at the sub-megahertz range [1417]. Recently, low-frequency squeezing was found to be interesting for electromagnetically-induced transparency-based quantum information protocols and other applications at atomic transition wavelengths [16]. Our work [17] is derived from this motivation and inspired by previous work such as the creation of beams with a low-frequency quantum correlation based on FWM in a hot rubidium vapor [18].…”