A quantum system can possess a property called magic. It's not about tricks: it's a measure of how hard it is to reproduce its behavior on a classical computer. Ordinary states, known as stabilizer states, are easy for a computer to handle. But states with magic leave it stumped. The problem is that checking for magic usually means measuring the system inside and out — a laborious and expensive process.
The authors of the new work propose skipping those complex measurements. They note that any stabilizer state has a minimum energy limit. If you measure the system's energy and it falls below this limit: that's it, you've got a magic state. This approach works when energy speaks clearly. But sometimes the energy is within normal bounds, and magic is still there.
That's when the second method comes in — via heat. You connect the system to a thermal bath and see how much heat it gives off or absorbs. For stabilizer states, heat exchange is bounded by a strict limit. If the measured heat flow exceeds that bound — magic is detected. The authors tested the method on various systems: from tiny ones where heat reveals magic even when energy is silent, to a chain of magnetic moments where the gap between ordinary and magic states becomes largest at the phase transition point.
The term 'magic' in quantum physics appeared in 2014 and quickly became standard. It denotes the resource that distinguishes quantum computers from classical ones.
In Greg Egan's novel 'The Permutation City', the protagonists seek ways to bypass the limitations of classical computation to simulate consciousness. Quantum magic is exactly the kind of resource that could help them.