Store quantum information by super-cold atoms

Scientists in the US have demonstrated a new experiment of "light-switch" in optical fiber that could become a new tool in the telecommunications and communications industry. The component was created by Michal Bajcsy (Harvard University, USA) and his colleagues, which can be developed to share information in both classical and quantum ways (Phys. Rev. Lett. 102, 203902 ).

Quantum information systems can bring about a revolution in global data information sharing by encrypting, processing and transmitting information using quantum mechanical properties. However, because a series of ' 1s ' and ' 0s ' is represented by the quantum states of individual subatomic particles, such as the polarization of photons, they become too sophisticated and easy to be lost information. The first experimental quantum component was developed but if it comes to commercial applications it requires systems that are too messy to compete with the classical technologies being used.

A universal approach is to transmit quantum states of photons through interaction with matter, which will act as intermediate elements. Here, photons with individual states are absorbed by an atom before being re-emitted in the same state or related state. But one difficulty arises, when trying to transmit information within a considerable distance, because scattering photons produce a rather large signal loss.

Figure 1 . Model of the experiment: Rubidium ultracold atoms are confined in a photonic crystal fiber core with a magnetic field dipole trap (Credit: Alan Stonebraker) .

Over the past few years, several research groups have proposed a way around this problem by transmitting photons through an empty optical fiber filled with vapor of atoms. The state of the atom changes by interacting with photons that make the fiber transparent, or become opaque with light - that is, an optical lock. However, when introducing a small percentage of atoms in empty space, a large number of photons are in fact never in contact with atoms and the loss problem still occurs. Bajcsy and his colleagues found a solution to this problem by replacing steam with ultracold rubidium atoms .

By retaining atoms in a solid magnetic field configuration (called 'dipole trap'), they can direct photon pulses into atoms with a probability of enhancing large collisions. destination . Initially, the fiber was almost transparent to allow light to pass through because there were no atoms there. Then, after closing the pulse, only 800 photons were pumped into the fiber, the atoms absorbed those photons and the system became completely opaque.

Figure 2 . Experimental results: a) Four-level system for nonlinear opening and closing processes, b) Transmission pulses, c) Transmission of pulses in optical fiber when present (blue), and not present (red) closed field open, d) the transmittance as a function of the number of photons, e) the number of photons recorded as a logical function of the presence (1) and not present (0) of the probe and the collapsing pulse (Phys. Rev Lett. 102, 203902).

' The challenge is to integrate the supercooled atomic technology developed over the past 20 years into an empty optical fiber in the same experimental system, ' Bajcsy told Physicsworld. The experiment was conducted at the MIT-Harvard Center for ultracold atoms (MIT-Harvard Center for Ultracold Atoms), in a collaborative study between Mikhail Lukin's research teams and Vuletic Vladan. To begin the experiment, a cloud of ultracold rubidium atoms was imprisoned with a laser beam before being directed into the fiber by a magnetic field.

' Burning atoms is always quite confusing and often the hardest part is simply to know where the atoms are ' - says Andrew Dawes, a researcher of super-cold atoms at Pacific University, Oregon.Bajcsy and his team are continuing to develop this study by combining their cold atoms with the technology of stopping pulses of light, to proceed to storing and transmitting data. death.

The results of the study can be found in the article just published in Physical Review Letters .