In a collaboration between the University of Aurges and the University of Southern Denmark, the researchers discovered a way to subtract individual quantum lights from laser pointers. This work was recently published in the Physical Review Letters. This method lays the foundation for future quantum communication and computing technology applications. Light is made up of tiny, indivisible energy packets, so-called photons. One of the defining properties of photons is that they do not interact with each other, they simply transfer to each other and are not affected at all. In the context of quantum communication, this is a very useful feature because it can ultimately achieve low-loss optically encoded data transmission over very large distances.
However, many emerging quantum information processing ideas will greatly benefit from the ability to make two photons interact, thereby affecting the propagation or state of another laser pointer. In recent years, ultra-old atomic gases have proven to be an ideal medium for manipulating light. For example, using a technique called electromagnetically induced transparency, researchers can drastically change the speed at which light travels, slowing it down to a surprisingly slow speed of a few meters per second. More importantly, light can be stopped by converting photons into atomic excitation in the medium. By reversing this process and mapping the excited states back to photons, this process implements a photon quantum memory, where photons can be temporarily stored and retrieved as needed
Odense's experimental team, together with a team from Allhall University and partners from the University of Maryland's Joint Quantum Institute, has realized such a photon memory, but there is a special form of atomic gas in which the constituent atoms Strong interaction. This effectively enables photons to detect each other in quantum memory, enabling researchers to manipulate light at a non-linear level. Using this idea, the team designed and demonstrated a novel method that uses another beam of light to subtract a single photon from the beam. The general idea is to store one light field before transferring another light field through the medium.
In the second photon, the photons detect the photons stored in the laser pointer and interact with them in such a way that a single photon is labeled and then discarded during retrieval. Deprived of a single photon, the original beam was left in a special quantum state, which has many scientific and technical applications in itself. In fact, the basic idea of manipulating photons with this non-linear quantum memory is promising for many applications in quantum information science. More research is needed before this capability becomes fully practical, but the photon tractor demonstrated is an important milestone in quantum technology based on interacting photons.