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Europhysics Letters (EPL)

Generation of Twin Photon Beams in a Ring Four-Wave Mixing Oscillator

Marc Vallet, M. Pinard, G. Grynberg

Published Apr 15, 1990• 49 citations
Publisher

Abstract

We show that a ring four-wave mixing oscillator operating above threshold can generate twin photon beams. The experiment is done with sodium vapour and the output power of the oscillator is of the order of a few milliwatts. The noise power measured on the intensity difference between the two generated beams exhibits a quantum noise reduction of 10%.

DOI
10.1209/0295-5075/11/8/008

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We show that a ring four-wave mixing oscillator operating above threshold can generate twin photon beams. The experiment is done with sodium vapour and the output power of the oscillator is of the order of a few milliwatts. The noise power measured on the intensity difference between the two generated beams exhibits a quantum noise reduction of 10%.
There is presently a growing interest in nearly degenerate four-wave mixing, both for application in optical phase conjugation and the generation of squeezed states. In particular, the self-oscillation of a system interacting with one or two pump beams has been investigated in great detail in the case of photorefractive materials, but very few experiments have been done in vapors in the cw regime. The results that we obtained using sodium are presented here. They are strikingly different from the results obtained with photorefractive materials. For example, the oscillating beam and pump beam frequencies coincide with a precision better than 10−2 Hz. Another interesting aspect of this oscillating beam is that it exhibits a phase sensitive noise: just above threshold, the noise on one quadrature of the field can be 10−2 times smaller than the noise on the other quadrature.
Using a simple scheme based on nondegenerate four-wave mixing in a hot vapor, we generate bright twin beams which display a quantum noise reduction in the intensity difference of more than 8dB8\phantom{\rule{0.3em}{0ex}}\mathrm{dB}8dB. The absence of a cavity makes the system immune to external perturbations, and strong quantum noise reduction is observed at frequencies as low as 4.5kHz4.5\phantom{\rule{0.3em}{0ex}}\mathrm{kHz}4.5kHz and over a large frequency range.
This chapter provides a review of both theoretical and experimental results that are obtained on the Non-Degenerate Optical Parametric Oscillator above threshold operation. In particular it is shown that most of oscillator's characteristics can be understood from the fact that the non-linear crystal emits highly correlated twin photons. The chapter studies the correlation properties between the intensities of the corresponding twin fields. It provides a simple treatment in terms of “corpuscular” photons and gives a proof of the corpuscular model in a fully quantum manner. The chapter provides a classical representation of the fields but in which vacuum fluctuations are properly accounted. This “classical” approach yields the noise spectra of the various measurable quantities in the general case. The chapter presents observation of quantum noise reduction on the difference between the intensities of the two twin beams. It deals with new possible applications of the twin photons to spectroscopy and to the generation of amplitude squeezed laser beams.
Using four-wave mixing in a hot atomic vapor, we generate a pair of entangled twin beams in the microsecond pulsed regime near the D1 line of 85 Rb, making it compatible with commonly used quantum memory techniques. The beams are generated in the bright and vacuum-squeezed regimes, requiring two separate methods of analysis, without and with local oscillators, respectively. We report a noise reduction of up to 3.8 ± 0.2 dB below the standard quantum limit in the pulsed regime and a level of entanglement that violates an Einstein–Podolsky–Rosen inequality.