23/02/2021 at 11:52 AM #25905Anonymous UserParticipant
One entanglement can hide another!
A theoretical physicist from IPhT and his partners from EPFL (Switzerland) and MIT (United States) demonstrated a temporal form of quantum entanglement which enabled them to demonstrate, for the first time, a very strong entanglement between a and one , in one of at ambient. Their experiment allows to probe the coherence of single phonons at scales of very short, which paves the way for of for ultra-fast quantum technologies.
The entanglement (or entanglement) of two distant quantum states may well be more and more popularized with the general public, it remains difficult to grasp. In its most “simple” version, two distinct photons are “united” in the same , which is manifested by a close correlation between their states of individual. While the measure of the first reveals a random polarization, the second is always polarized in the same direction as that of its “” !
Physicists have imagined two “nested” intricacies, much more difficult to describe. The first brings together a photon and a of crystal vibration (phonon). The emission of the photon is very strongly correlated with the creation of the phonon but their is out of reach. The second entanglement brings together two photon-phonon pairs created successively. While the photon measurement (possible this time) reveals a random creation time, the phonon is always created at the same !
Result: the measurements of these temporally entangled states violate the “”, which proves, not only the of the entanglement between the two instants of creation of the photon-phonon pairs, but also that of the entanglement photon and phonon, which is a world first.
This experiment also enabled researchers to measure the duration of coherence of a single phonon (a few picoseconds) despite its shortness. The technique used can be applied to all kinds of crystals (powders, synthetic materials, etc.). Perhaps she will reveal, a , a which will lend itself to the development of ultra-fast quantum technologies …
How is photon-phonon entanglement produced?
A diamond crystal at room temperature is illuminated by two pulses successive ultra-short (write and read), separated by a few picoseconds (10-12 s). Their lengths are tuned precisely on levels of of the diamond.
Very rarely, one of the write photons is converted into a vibrating quantum of the crystal (phonon) and a lower energy photon (Stokes photon). In this case, a few picoseconds later, a read photon is absorbed along with the phonon by the crystal, which emits a higher energy photon (anti-Stokes photon).
These events occur very rarely (once in a thousand), despite the large of photons making up the ultra-short laser pulse. But when they do occur, the creation of a Stokes photon is always accompanied by the creation of a phonon. The number of Stokes photons is therefore closely correlated with the number of phonons, itself closely correlated with the number of anti-Stokes photons. These correlations are quantum in nature: the Stokes-phonon is entangled in where it is both absent and present. This leads to entanglement of the Stokes photon-Anti-Stokes photon pairs, which is difficult to demonstrate experimentally.
What does the temporal entanglement of the two photon-phonon couples consist of?
In order to overcome this difficulty, the researchers use two successive sets of write-read pulses (early and late), separated by 3 nanoseconds (10-9 s), each set being capable of generating photon-phonon pairs. They demonstrate that the creation time of the Stokes and anti-Stokes photon pairs is indefinite: the pairs are therefore temporally entangled.
Everything happens as if the form of entanglement by presence (there is a photon-phonon couple) or absence (there is no photon-phonon couple) were transformed into temporal entanglement between (there is a couple of Stokes photons). anti-Stokes early) and (there is a pair of Stokes-anti-Stokes late). The measurements show that these two states are possible simultaneously.
In addition, it is possible to probe the coherence time of the phonon by varying the time difference between the write and read photons.
References – correlations between light and vibration at ambient conditions, Advances
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