Russian physicists from the Skolkovo Institute of Science and Technology have developed a new method that allows, by combining quantum and classical computations, to calculate the dynamics of large quantum systems. The method has been successfully applied to problems of nuclear magnetic resonance.
As you know, any material object around us consists of atoms, and atoms - of negatively charged electrons and positively charged nuclei. Many atomic nuclei, in turn, are tiny magnets that can be excited by a radio frequency magnetic field, a phenomenon known as nuclear magnetic resonance. It was discovered in the first half of the twentieth century and since then, for its discovery and application, five Nobel prizes have been received. Its most famous application is magnetic resonance imaging.
Despite more than half a century of history, there are still unsolved problems in the theory of nuclear magnetic resonance. One of them is the quantitative prediction of the response of nuclear magnetic moments in solids to a disturbance by a radio frequency pulse. This problem is a special case of a more general problem of describing the dynamics of systems consisting of a large number of quantum particles. Direct computer simulation of such systems requires enormous computational resources that no one possesses.
An approximate approach to describing many-particle systems is to use quantum physics only to model the central part of the system, while the rest of the system is modeled classically, that is, without quantum superpositions. However, in this approach, combining quantum dynamics with the classical one is a nontrivial task due to the same quantum superpositions: while the classical system is in only one state at a time, a quantum system can be in several states simultaneously: it is not clear which of states in superposition due to the action of the quantum part of the system on the classical one.
Skoltech researchers, graduate student Grigory Starkov and Professor Boris Fine, have succeeded in proposing a hybrid computational method that combines quantum and classical modeling. The idea is to compensate for the effect of the averaging effect of quantum superpositions on the classical environment without breaking the most important dynamic correlations. The method has been thoroughly tested for various systems, both by comparison with direct numerical calculations, and directly with experimental results. It is expected that the method will significantly expand the ability of scientists to simulate the magnetic dynamics of nuclei in solids, which, in turn, will help study complex materials using nuclear magnetic resonance methods.
Alexander Ponomarev