Quantum physics

To What Extent are Twin Photons Really Twins?

Joint work by Onera and the Kastler Brossel laboratory is leading to progress in knowledge of “twin” photons, with the promise of new quantum applications. 

When a beam of light passes through certain materials (referred to as non-linear), the photons of the beam spontaneously split into two photons, referred to as “twins”. This is a purely quantum effect.

These twin photons are the basis of new quantum technologies such as quantum cryptography, entanglement and teletransportation.

The question of the simultaneity of the creation of the two twin photons has been present since the discovery of this effect in the 1970s. A joint team from Onera, the Kastler-Brossel Laboratory of the Ecole Normale Supérieure and the Charles Fabry Laboratory of the Institute of Optics Graduate School has just answered it.

For their work they used another purely quantum effect, two-photon absorption: only the simultaneous presence of two photons allows for the transition of an electron between two energy levels. Accuracy of measurement: of the order of 1 femtosecond (0,000 000 000 000 001 s or 10-15 seconds).

By using this technique the researchers determined a time lag of less than 50 fs between the births of the two twin photons. The results have just been published in the journal Nature Communications.

This work is based in particular on the thesis of Fabien Boitier, defended at Onera at the beginning of 2011 (prize for the best thesis of the Physics branch of Onera in 2010)

The same Onera team, lead by Antoine Godard, had published in 2009 in the equally prestigious journal Nature Physics on a related subject. [See our press release (in French: "Onera experimentally verifies Glauber’s theory of Quantum Optics: photons have a natural tendency to aggregate"]

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