Swiss physicists were the first to demonstrate the Einstein-Podolsky-Rosen paradox (EPR paradox) on a quantum system consisting of 600 rubidium atoms. Scientists have succeeded in breaking local realism by entangling two parts of a supercooled gas cloud and proving the possibility of steering, when the state of one part of a quantum system can be predicted from the state of the other. The article by scientists was published in the journal Science, Science Alert reports.
According to the EPR paradox, proposed in 1935, two particles can interact with each other in such a way that their position and momentum can be measured with an accuracy greater than that allowed by the Heisenberg uncertainty principle. For example, the total momentum of two particles (A and B), which were formed as a result of the decay of the third, should be equal to the initial momentum of the latter, therefore, measuring the momentum of particle A allows you to find out the momentum of particle B, while no disturbances are introduced into the motion of the second particle. Then it is possible to accurately determine the coordinates of particle B, thus violating the Heisenberg uncertainty principle.
Since the uncertainty principle remains in any case, the measurement of the momentum of particle A inevitably introduces perturbations in the coordinates of particle B, making them uncertain, no matter how far the first particle is from the last. Einstein believed that this violates the realism of the world and physical objects in the framework of quantum mechanics cease to objectively exist. He believed that such an interpretation is incorrect and the probabilistic nature of the behavior of particles is actually explained by the existence of some hidden parameters. However, to date, the theory of hidden parameters has not received experimental confirmation.
Scientists have created a Bose - Einstein condensate of about 600 rubidium-87 atoms. The condensate is a gas cooled to ultra-low temperatures, in which all atoms occupy the minimum possible quantum states, that is, they become almost indistinguishable from each other. With the help of a laser, the atoms were brought into a compressed state, in which fluctuations of one variable (in this case, one of the components of the spin, that is, the "axis of rotation") become very small, while the other becomes large. Thus, a quantum bond was created between the atoms.
The researchers managed to split the cloud into two different regions - A and B. Using lasers, the collective spin of atoms in the condensate and the components of the "axis of rotation" were measured. In this case, based on inequalities that take into account these parameters, entanglement between atoms was proved for the squeezed state and a given collective spin. The correlation turned out to be so strong that an EPR paradox arose and it was possible to predict the quantum state of atoms in region B by measuring the spin in region A (prediction is possible only in one direction).