Competition for cosmic quantum mixers

When information crosses the event horizon of a black hole, it is lost: Within a very short time, it is entangled with the other quantum information there and "smeared" across the entire black hole. Gravity monsters are considered to be the fastest and most efficient "quantum mixers" in the universe. However, it is now becoming apparent that much simpler systems are competing with them.

As a team led by Peter G. Wolynes from Rice University in Houston now reports, information can be lost in chemical reactions almost as quickly as when an event horizon is crossed. An exotic quantum effect, "tunnelling", suddenly makes enormous quantities of random quantum states possible, the experts write in the scientific journal "PNAS". This could destroy information within fractions of a trillionth of a second.

The working group used theoretical calculations to investigate how this quantum information behaves during the reaction. This is an important question in physical chemistry: chemical reactions can be controlled by the states of the molecules involved. From a quantum mechanical point of view, a reaction is not a sequence of unambiguous states, but rather represents a whole landscape of states that can be assumed with different probabilities. The quantum information of the initial molecules is effectively contained in these probabilities.

Under certain circumstances, the comparatively manageable landscape of states and their probabilities suddenly becomes an unmanageable universe of possibilities. This happens when a chemical system is cold and slow enough so that it can "tunnel". This means that it switches between two states, even if it does not actually have enough energy for this transition. In quantum mechanics, such "impossible" transitions can also occur with a low probability. If this happens, the quantum information about the initial state is smeared across the entire system at the theoretically highest possible speed, much like in a black hole.

However, this does not always happen - unlike with black holes, the process depends heavily on the circumstances. If a reaction takes place in a large and complex system, for example in water, then the environment dampens the effect. Chemistry is therefore by no means helpless in the face of information loss. The extent to which information is retained in the course of a chemical reaction can be controlled in principle - and thus also how well chemical processes can be controlled and how effectively the desired products can be obtained. This is also a difference to a black hole: if you fall into one, it always leads to the same result - whether desired or not.

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