Scientists invent holographic atomic memory to generate large photons on demand

The holographic atomic memory invented and manufactured by physicists at the Department of Physics in Warsaw University is the first device that can generate single photons on-demand with tens or more per group. This device, which has been successfully proven, overcomes one of the fundamental obstacles encountered in the construction of certain types of quantum computers.

Fully secure high speed quantum communication, and even quantum computer modeling, is one of the possible applications of the new single-photon sources recently manufactured by the University of Warsaw, UW. An unprecedented feature of this new device is that for the first time, it enables us to generate precisely controlled photon clusters on demand.

"Compared to existing solutions and ideas, our devices are more efficient and can be integrated more on a large scale, and in function we can even think of it as the first small job to be done in a single photon "ICs," said Wojciech Wasilewski, Ph.D., Department of Physics, University of Warsaw, is one of the authors of an article published in the scientific journal Physical Review Letters.

The core of photons generated in this system is a glass cell filled with hot gas vapors. Irradiating this cell with a laser will cause it to emit photons with wavelengths in the infrared spectral range.

The first single-photon source was invented in the 1970s, but many of the existing types of single-photon sources still have many drawbacks. Nevertheless, the single-photon can still be successfully applied in quantum confinement Communication protocol. However, in order to be able to perform complex quantum calculations, we need the entire photon population.

The easiest way to generate photons is to use enough light. The most widely used device today exploits the phenomenon of spontaneous parametric downconversion (SPDC). Under certain conditions, a photon produced by a laser can be split into two new photons, each with only half the energy. The other properties of the two photons are determined by conservation of energy and conservation of momentum. Therefore, when we record this information about a photon in a photon, we can also know the existence and properties of another photon, while the other photon is not disturbed by the observation, so it is very suitable for quantum manipulation. Unfortunately, the process of converting a light source to a single photon for each light parameter is very slow and completely random. Therefore, even if we only want 10 light sources to launch simultaneously, we may also need to wait a few years.

In 2013, a group of physicists from the University of Oxford and the University of London proposed a more efficient protocol for generating photon populations. The idea is to place a quantum memory on each light source that is capable of storing emitted photons. Photons stored in memory can be released at the same time. The calculations show that the time scale required to wait for a photon group of 10 photons will be shortened by a staggering order of ten orders: a few microseconds from years!

Now this light source from the University of Warsaw's physicist is the first practical example of this concept and a more integrated example: Here all photons follow a laser that lasts only a few microseconds Pulsed irradiation occurs immediately within the quantum memory. Here, the external single photon source is no longer needed, and the number of quantum memories required has also been reduced to only one.

"Our entire experimental setup took up about two square meters of the surface of our optical platform, but the most important thing happened in the memory itself in a glass cylinder about 10 cm in diameter and about 2.5 cm in diameter. There's something as complex as a semiconductor IC in this cylinder, but one can get disappointed: the small, cylindrical cavity is filled with 87Rb rubidium atoms at 60 to 80 degrees Celsius, "Michal Dabrowski, a doctoral student at the Department of Physics, Warsaw University .

The new memory, made with the resources of the PRELUDIUM and SONATA projects funded by the Polish National Scientific Research Center and funded by the Warsaw PhoQuS project, is a spatial multimode memory: a single photon can be placed, stored, manipulated and read in different areas within a cylinder , Like a separate storage drawer. Written by a laser beam to complete, in the form of atomic excitation to maintain a specific spatial model - hologram - to achieve. Illuminating the system with a laser allows us to reconstruct the hologram and read the contents of the memory.

In the experiments that have been conducted, this new light source produces a group of photons of up to 60 photons. Calculations show that under realistic conditions, the use of higher power lasers will help increase this figure, even up to a few thousand. (The calculations involved in this experimental data analysis are so complex that they require the computational power of 53,000 grid cores that use the PL grid infrastructure).

Due to noise, loss and other parasitic processes, this quantum memory developed by the Department of Physics, Warsaw University, can store photons in the tens to tens of microseconds, which seems to be a short time for humans. However, there are systems that allow easy manipulation of photons on the nanosecond time scale. In the new quantum memory, in principle we can perform hundreds of operations per photon, which is sufficient for quantum communication and information processing.

Having a working light source with such a large group of photons has taken us a significant step toward making a class of quantum computers that can perform some computations much shorter than the best modern computers do. Years ago it has been shown that by performing simple linear optics on photons we can increase the speed of quantum computation. The complexity of these calculations depends on the number of photons processed at the same time. However, the lack of light sources that generate large groups of photons impedes the ability of linear quantum computers to expand their range of applications, making them confined to elementary math operations.

In addition to quantum computing, photonic "integrated circuits" may also be used for quantum communication. Currently, this involves the use of optical fibers to send single photons. The new light source will make it possible for many photons to enter the fiber at the same time, thus increasing the capacity of the quantum channel.

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