For the first time, the effects of the "impact" of photons on microscopic particle collisions were measured by the Swiss physicists. These shocks give a basic limit, limiting how particles in an optical trap cooldown. A better understanding of this effect will result in experimentally creating a capture particle with a good quantum state definition. Such particles can be used to study how this state develops under the influence of gravity. By a potential energy generated by the laser electromagnetic field, a particle can be confined to the optical trap. Restricted particles undergo a harmonic motion whose amplitude depends on its energy. Individual atoms and ions can be processed separately by the laser, and their quantum states can be manipulated by photons. In most cases, however, the heating mechanism of the dominant trapped macroparticle is a thermal collision with the remaining gas molecules remaining trapped in the evacuated trap. Feedback cooling In a recent experiment, led by Lucas Novotny of the Federal Institute of Technology in Zurich, the research team used infrared lasers to confine silica nanoparticles with a radius of about 50 nm to light traps, Before sucking up almost all the air created the ultra-high vacuum chamber. Researchers use a process known as feedback cooling, in which the position of the capture particle is monitored and the trap frequency is modulated accordingly, drawing off the energy of particle motion and lowering the temperature of the particle to the micro-Kelvin level. At pressures greater than 10e9, they found that the minimum temperature they could reach was stress-dependent. However, at this point, the researchers found that the minimum achievable temperature approaches a lower limit, no matter what the pressure. This means, they say, that under the very low pressures, the dominant reason for limiting cooling is the electromagnetic noise in the trap. Recoil energy For further investigation, the research team turned off the feedback cooling process under very low pressure, allowing trapped photons to freely heat its particles. The difference between the energetic states of the oscillating particles is greater than the magnitude of each photon collision recoil energy, so the simplest energy of photon scattering does not affect the elastic particles. However, sometimes photons try to excite the nanoparticle to a higher state of oscillation, heating up. The warming process is random, but by repeating them multiple times and averaging their results, researchers succeeded in producing a smooth warming curve showing particles heating faster when trapped in a higher-power laser . "This really shows the difference from hot melt, which is a collision with gas molecules," Novotini said. "Of course, the hot melt does not depend on the laser power," the researchers also showed that the heating rate is different from the hot melt expectancy and that it depends more strongly on the particle size. Height of the fruit The team is now looking for ways to make the particle temperature lower until its quantum nature becomes truly measurable. It would be very interesting under such circumstances, Nowotini said, shutting down the laser and tracking the particle's behavior. "We know when and where particles should end, and any spillover will indicate that there must be additional terms that generate heat or decoherence or something else." Novotini said the ultimate goal is to see the impact of gravity on the quantum state of the particle. "We have a huge particle here and we feel the gravitational force: If we release it in a trap, it falls, and we can prepare the particle in the desired quantum state and measure how the quantum state is under the influence of the gravitational field I think this is the true Holy Grail in the study, but it is a fruit hanging above! " Andhra Jelavic, of the University of Nevada at Reno, who was not involved in the study, said he has been predicting this effect all along. "Now that we have seen a demonstration, and there is a good agreement between theory and experimental conclusions, it can be predicted that what they presently show will only be a level-limiting one," he explained. "One of the goals of their research team, our research team, and many others in the field is to try to cool the particles to their quantum base state and we still have to overcome that mechanism and now it can measure and make us Good understanding, I think it will guide researchers to understand what is really necessary to circumvent this restriction. " This research has been published in the Physical Review Letters magazine.