The research produces intense light beams with quantum correlations

The properties of quantum states of light are already exploited by highly sophisticated cutting-edge technologies such as those of the latest sensitivity updates to LIGO, the Laser Interferometer Gravitational-Wave Observatory, implemented to detect gravitational waves since September 2015, or encryption keys used for satellite safety on board.

Both solutions use crystals as noise-free optical amplifiers. However, the use of atomic vapors has been considered a more efficient alternative that improves the accessibility of non-classical light states.

“We show that oscillators based on these atomic amplifiers can generate intense light beams with quantum correlations,” said Marcelo Martinelli, researcher at the Institute of Physics at the University of São Paulo (IF-USP). Martinelli is co-author of an article published in Physical Review Letters describing the main results to date of a thematic project of which he is the principal researcher and which is supported by the São Paulo Research Foundation – FAPESP.

Both crystals and atomic vapors can be used to produce pairs of quantum correlated light beams. Investigating the behavior of these sources is a challenge. The behavior of light below a certain power level is similar to that of light produced by a light bulb. Above a certain threshold, its characteristics are similar to those of a laser. “It is as if crystals or atomic vapor convert the light of a lamp into laser light. It is easier to investigate this transition in the atomic medium than in the crystalline medium since it is possible to produce more intense beams in an atomic medium,” said Martinelli.

For this purpose, optical cavities are used. By controlling the geometry of the cavity and the temperature of the atomic vapor, Martinelli and collaborators were able to produce photon coupling in more open cavities.

“This offered two advantages over older crystal-based cavities: higher quantum efficiency so that the number of photons delivered by the output window easily exceeded the number of photons lost in the environment, and the ability to investigate finer details of the transition between light with heterogeneous frequencies and the production of intense laser beams. It was as if we had opened a window into the quantum dynamics of the phase transition, “said Martinelli.

Potential applications include high-precision metrology with the manipulation of quantum noise in light and the encoding of information via quantum entanglement.