Quantum Fluctuations in Light Beams

L. Mandeļ

Federico Casagrande, L. A. Lugiato

E. Giacobino

In recent years physicists have had significant success in manipulating the quantum fluctuations of light, which originate in Heisenberg's uncertainty principle. They have produced squeezed light, that is light with reduced noise in its intensity or in its phase, and “twin beams” – two light beams having correlated intensity fluctuations. A new world record in twin-beam correlation has now been set by Orhan Aytur and Prem Kumar at Northwestern University, USA (Phys. Rev. Lett. (1990) 65 1551).

Alessandro S. Villar

Very low intensity and phase fluctuations are present in a bright light field such as a laser beam. These subtle quantum fluctuations may be used to encode quantum information. Although intensity is easily measured with common photodetectors, accessing the phase information requires interference experiments. We introduce one such technique, the rotation of the noise ellipse of light, which employs an optical cavity to achieve the conversion of phase to intensity fluctuations. We describe the quantum noise of light and how it can be manipulated by employing an optical resonance technique and compare it to similar techniques, such as Pound–Drever–Hall laser stabilization and homodyne detection.

Harry J. Kimble

Vincent Boyer, Alberto M. Marino, Raphael C. Pooser +1 more

Abstract Nonlinearities in atomic vapors allow the production of “entangled images”—beams of light whose transverse light distributions exhibit localized correlations in their unavoidable quantum fluctuations (see picture). These spatially entangled beams may prove useful to reduce the noise in absorption imaging and beam positioning below the quantum noise level, as well as for quantum information applications. magnified image The entanglement properties of two beams of light can reside in subtle correlations that exist in the unavoidable quantum fluctuations of their amplitudes and phases. Recent advances in the generation of nonclassical light with four‐wave mixing in an atomic vapor have permitted the production and the observation of entanglement that is localized in almost arbitrary transverse regions of a pair of beams. These multi‐spatial‐mode entangled beams may prove useful for an array of applications ranging from noise‐free imaging and improved position sensing to quantum information processing.