An ordinary proton consists of three quarks, like a three-legged stool. But nature does not forbid assembling a 'chair' from four quarks, if two of them are heavy beauty quarks and two are light. Such particles are called tetraquarks, and until now they have been studied mainly at large accelerators, by colliding particles and sifting through the debris.
Now physicists have tried a different approach: they rewrote the four-quark problem in the language of quantum bits and ran the calculation on a quantum computer. Instead of accelerating particles, they calculated how quarks attract and repel each other using quantum computing. It turned out that the most robust 'gluing' occurs when two beauty quarks and two light quarks form a state with zero total spin and positive parity. Such a particle lives longer than other configurations, and its mass matched predictions from old, well-tested models.
This calculation is the first demonstration that quantum simulation is suitable for searching for exotic particles. Previously, such problems were considered too complex for modern quantum processors. Now the door is open to studying entire families of four-quark states that may be hiding in data from future experiments.
A tetraquark with two beauty quarks is about three times heavier than a proton, but lives billions of times shorter — only a tiny fraction of a second.