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Conference on Lasers and Electro-Optics

Quantum-correlated Light Source from Dual-seeded Four-wave Mixing with a Diode Laser System

Meng-Chang Wu, Nicholas R. Brewer, Rory W. Speirs, Bonnie L. Schmittberger, K. M. Jones, Paul D. Lett

Published May 5, 2019• 0 citations
Publisher

Abstract

We have obtained broadband intensity-difference squeezing from sub 10 Hz to 20 MHz via four-wave mixing (4WM) in a rubidium vapor. This was accomplished by dual-seeding the 4WM process and using semiconductor diode lasers. © 2019 The Author(s)
DOI
10.23919/cleo.2019.8749904

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We study a variety of mechanisms that introduce noise into squeezed light generated by a four-wave mixing (4WM) process in Rb vapor. The noise from the seeding beam itself is a general noise that appears in any squeezed light generated from a seeding process. This noise dominates in the squeezed light at acoustic and lower measurement frequencies. A second excess noise source is observed in the twin beams pumped by either a diode laser system or a Ti:sapphire laser system. This excess noise is much stronger in the diode laser systems. It is present in the twin beams at measurement frequencies when the 4WM gain is reduced toward unity. Most of this excess noise can be removed with a dual-seeded 4WM scheme. A third noise source we examine is from a two-beam coupling that degrades the squeezing of the dual-seeded 4WM process at low frequencies of the order of the atomic transition linewidth. This noise can be avoided by seeding skew rays in the 4WM gain region. This gives us an insight to solve this "cross talk" problem by imaging the source in the 4WM gain region. In addition to studying noise sources, we propose a gain-independent calibration scheme that relies on higher order correlation function for the absolute calibration of photodiodes. Having low frequency squeezing is really important if we record quantum images with a CCD camera, which has a slow shutter speed. Also, it's been very difficult for people to get low-frequency squeezing. We obtain a record level of low-frequency squeezing using a simple dual-seeding technique. With this study of noise sources we are closer to having a portable quantum light source using diode lasers.
Using a nondegenerate four-wave mixing process in hot rubidium vapor, we demonstrate a compact diode-laser-pumped system for the generation of intensity-difference squeezing down to 8 kHz with a maximum squeezing of -7 dB. To the best of our knowledge, this is the first demonstration of kilohertz-level intensity-difference squeezing using a semiconductor laser as the pump source. This scheme is of interest for experiments involving atomic ensembles, quantum communications, and precision measurements. The diode-laser-pumped system would extend the range of possible applications for squeezing due to its low cost, ease of operation, and ease of integration.
We report the generation of strong, bright-beam intensity-difference squeezing down to measurement frequencies below 10 Hz. We generate two-mode squeezing in a four-wave mixing (4WM) process in Rb vapor, where the single-pass-gain nonlinear process does not require cavity locking and only relies on passive stability. We use diode laser technology and several techniques, including dual seeding, to remove the noise introduced by seeding the 4WM process as well as the background noise. Twin-beam intensity-difference squeezing down to frequencies limited only by the mechanical and atmospheric stability of the lab is achieved. These results should enable important low-frequency applications such as direct intensity-difference imaging with bright beams on integrating detectors.
Using a nondegenerate four-wave mixing (FWM) process based on a double-Λ scheme in hot cesium vapor, we demonstrate a compact diode-laser-pumped quantum light source for the generation of quantum correlated twin beams with a maximum squeezing of 6.5 dB. The squeezing is observed at a Fourier frequency in the audio band down to 0.7 kHz which, to the best of our knowledge, is the first observation of sub-kilohertz intensity-difference squeezing in an atomic system so far. A phase-matching condition is also investigated in our system, which confirms the spatial-multi-mode characteristics of the FWM process. Our compact low-frequency squeezed light source may find applications in quantum imaging, quantum metrology, and the transfer of optical squeezing onto a matter wave.