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

Abstract

We review our recent experimental progress in quantum technology employing amplification effect of four-wave mixing in a rubidium vapor. We have produced an intensity difference squeezed light source at frequencies as low as 1.5 kHz which is so far the lowest frequency at which squeezing has been observed in an atomic system. Moreover, we find that the bandwidth of our squeezed light source can be controlled with light intensity pumping. Using our non-classical light source, we have further developed a nonlinear Mach-Zehnder (MZ) interferometer, for which the maximum fringe intensity depends quadratically on the intensity of the phase-sensing field at the high-gain regime, leading to much better sensitivity than a linear MZ interferometer in which the beam splitters have the same phase-sensing intensity. The quantum technologies developed by our group could have great potential in areas such as precision measurement and quantum information. Bull, 2012Bull, , 57: 19251930, doi: 10.1007 Photons are natural fast carriers of quantum information. For this reason, much attention [1,2], particularly over the last two decades, has been drawn towards applications of quantum optical systems to quantum information processing, such as quantum communication and distributed quantum networks. The research necessitates high-quality quantum light sources that generate squeezed light with large noise suppression below the shot noise level (SNL) and entangled states. In 1985, Slusher et al. pioneered squeezed light generation based on four-wave mixing (FWM) in an optical cavity [3]. Since then, several methods have been explored to obtain squeezed states; a fundamental and frequently-used technique is the optical parametric oscillator consisting of nonlinear crystals and cavities to build up non-classical states very efficiently [4][5][6][7]. Using such methods, very strong single mode squeezing has been realized in the past few years. For example, vacuum squeezing levels of 10 dB were achieved in 2008 [8] and Mehmet et al. obtained up to 11.5 dB squeezing last year [9]. By contrast, without any optical cavity and mode cleaner, FWM has gradually become another popular method because of its simple experimental setup. Since the initial work of Lett's group in 2007 [10], as much as 9.2 dB squeezing has been reported in hot rubidium vapor [11]. Based on FWM, a pair of multi-spatialmode beams was produced, carrying two images which are in non-separable continuous-variable entangled states. The images were composed of "squeezed vacuum" twin beams

Gaussian-state interferometry with passive and active elements

“…The so-called SU(1, 1) interferometers [12][13][14] and the coherent-light-boosted interferometers [15,16] belong to this class. Quantum enhaced precision in active interferometers have been recently demostrated [17,18].…”

The squeezing dynamics of two independent atoms by detuning in two non-Markovian environments

“…[21] Some related work on atomic ensemble is also done. [22] On the other hand, it is well known that real quantum systems unavoidably interact with their environments, [23] then how to maintain the squeezing of open quantum systems for a long enough time to allow the performances of quantum measurements and quantum communications naturally becomes of great interest especially when it comes to a realistic description of experimental situations. Generally, the environment is classified as Markovian without memory and non-Markovian with memory.…”