Fundamental Research Division
The DRF at the CEA assemble approximately 6,000 scientists since January 2016.
Scientific result | Quantum Physics | Theoretical physics | Laser
A theoretical physicist at the IPhT and his partners at the EPFL (Switzerland) and MIT (USA) have just revealed a temporal form of quantum entanglement. For the first time, this has allowed them to demonstrate a very strong entanglement between a photon and a phonon, in a diamond crystal at room temperature. Their experiment makes it possible to probe the coherence of single phonons on very short time scales, which opens the door to the search for materials for ultrafast quantum technologies.
Even though the entanglement of two distant quantum states is more and more popularized among the general public, it remains a difficult concept to grasp. In its "simplest" version, two distinct photons are "joined" in the same quantum state, which is manifested as a close correlation between their individual polarization states. While the measurement of the first photon indicates a random polarization, the second is always polarized in the same direction as its "twin"!
Physicists have imagined two "nested" entanglements, which are much more difficult to describe. The first brings together a photon and a quantum of crystalline vibration (i.e. a phonon). The emission of the photon is very strongly correlated with the creation of the phonon, although it is undetectable. The second entanglement brings together two successively created photon–phonon pairs. While the measurement of the photon (which is possible this time) indicates a random creation time, the phonon is always created at the same time!
As a result, the measurements of these temporally entangled states violate the "Bell inequalities". This not only demonstrates the strength of the entanglement between the two moments of creation of the photon–phonon pairs, but also that of the entanglement linking the photon and phonon – a world first.
This experiment also allowed the researchers to measure the coherence time of a single phonon, despite its brevity (on the order of a few picoseconds). The technique they used can be applied to all kinds of crystals (powders, synthetic materials, etc.). And perhaps it can eventually be used to unveil a material suitable for the development of ultrafast quantum technologies ...
CEA is a French government-funded technological research organisation in four main areas: low-carbon energies, defense and security, information technologies and health technologies. A prominent player in the European Research Area, it is involved in setting up collaborative projects with many partners around the world.