Simulate, without trying to imitate nature

If some philosophers once questioned themselves about the state of human beings before the emergence of society, physicists sometimes wonder about the ground state of a material. What would the material look like if it were in its lowest energy state? This question is particularly relevant to understanding certain materials or molecules whose exotic properties are only revealed at low temperatures.  “Using a quantum computer to simulate the dynamics of a material, a system, to measure its evolution, its behavior, it is a known and controlled process. On the other hand, placing the object of study in its initial conditions is quite a challenge. “explains Professor David Poulin.

The tremendous computing capacity estimated for the quantum computer allows us to consider many breakthroughs in areas such as drug research, transportation and finance. In physics, in the search for new materials, one of the tasks that we want to give to the quantum computer is the simulation of the behavior of materials at low temperature, the ground state.

This is what Professor Poulin and his co-authors, including the very famous Professor Alexei Y. Kitaev of the Institute for Quantum Information and Matter (IQIM) at the California Institute for Technology, explored the idea that, for research purposes, it may be more promising to try to mathematically simulate the ground state rather than follow nature’s path.

Professor Poulin explains. “All that has been tested before is to reproduce nature in an algorithmic way.  For example, how do you cool a material in the laboratory? Just put it in contact with something cold, such as liquid helium, and the dynamics of the system will naturally cause it to cool down. In a quantum simulation, it is possible to imitate this dynamic of a system coupled to a cold tank, which allows us in principle to prepare it in ground state. However, this simulation is very slow and expensive, which is a major obstacle to this type of application. “The discovery of Prof. Poulin and his co-authors is an algorithm that makes it possible to prepare the ground state of a system without imitating a cooling process. Instead, the method uses a much more efficient mathematical trick to do the same work.  “What distinguishes our approach is that it is based on a process that does not occur in nature. It is a kind of algorithmic shortcut that allows us to simulate nature without imitating it. »

What the researchers have presented in this text is an innovation, it would not be unthinkable to adapt the same idea to go beyond the scope of the study of materials, for example to study complex molecules, or ongoing experiments in the large collider of CERN (European Council for Nuclear Research).