Multipass configuration for improved squeezed vacuum generation in hot Rb vapor

Abstract

We study a squeezed vacuum field generated in hot Rb vapor via the polarization self-rotation effect. Our previous experiments showed that the amount of observed squeezing may be limited by the contamination of the squeezed vacuum output with higher-order spatial modes, also generated inside the cell. Here, we demonstrate that the squeezing can be improved by making the light interact several times with a less dense atomic ensemble. With optimization of some parameters we can achieve up to −2.6 dB of squeezing in the multi-pass case, which is 0.6 dB improvement compared to the single-pass experimental configuration. Our results show that other than the optical depth of the medium, the spatial mode structure and cell configuration also affect the squeezing level.

Spiral bandwidth of four-wave mixing in Rb vapour

“…In our experiments we work in a regime, 2z R /L = 0.2, where the cell length L is significantly larger than the focal region of the pump beams ∼ 2z R . It is instructive to consider how the spiral bandwidth might change in situations with high-power pumps under a weaker focus, as in squeezing experiments 49 and related blue-light FWM experiments 17 . In Fig.…”

Quantized nonlinear Gaussian-beam dynamics: Tailoring multimode squeezed-light generation

“…As expected, there is no response in = 0 modes and we see a slight amount of squeezing in the higher-order p modes, but it is mostly concentrated in the u 0,0 mode. Several of our studies, using spatial masks [26] and optimization procedures [27], reveal the absence of any azimuthal structure (that is, = 0) and subtle pollution from higher-order p modes. But what if cross talk between the p modes is taking place?…”

“…The early work predicted levels of noise suppression which have proven to be woefully over optimistic. This realization prompted more rigorous noise calculations [46] and our experimental study of the transverse spatial modes excited during the interaction [26,27]. With our preceding theory, we are finally able to perform a fully second-quantized analysis of the transverse-spatial-mode structure.…”

“…This has prominently been done for squeezed light generated in atomic vapors via the polarization self-rotation effect (PSR) [18][19][20][21] and four-wave mixing (FWM) [22][23][24][25] processes. The squeezed vacuum generated via PSR has been studied experimentally using spatial masks [26] and optimized for various optical depths [27], in each case elucidating more about the spatial-mode structure of the noise suppression. Squeezing generated via FWM is typically harnessed as two-mode squeezing and spatial correlations between the twin beams have also been studied in detail [28][29][30][31].…”

Hybrid Entanglement between Optical Discrete Polarizations and Continuous Quadrature Variables

“…) is adopted on Bob's site, which can be attained with a two-mode squeezed vacuum state [28] in an excellent approximation. A small fraction of light in |ψ B (on average one photon) is tapped off by a beam-splitter (BS) with amplitude reflectivity r 1, and the state then evolves to (1 + r ĉ d † )|ψ B c |0 d with ĉ and d † being the annihilation and creation operators for modes c and d. Please note that ĉ|Cat ± = αN ∓ N ± |Cat ∓ .…”