A quantum computer isn't just a bunch of qubits: it's a whole city, where each resident is one of the machine's possible states. Residents get to know each other through weak interactions between qubits: if one state can transition to another, a thread of acquaintance is drawn between them. There are many such states, like people in a metropolis, but the connections between them aren't random.
The authors of the new study mapped these acquaintances for a quantum computer. It turns out the map looks like a social network: on average, any state is just nine 'handshakes' away from any other — roughly like the six degrees of separation between people on Earth. This 'small-world' property means information can spread quickly across the entire system.
This merging, it turns out, happens exactly when the quantum computer stops behaving predictably and descends into chaos. Previously, this could only be observed in small systems because the computations were enormously expensive. The new method allows us to peer into systems of up to thirty qubits, and see how quantum disorder is born.
The computer-city follows the same laws as human society: a few acquaintances connect everyone, and with enough sociability, a single network emerges. Understanding this network helps engineers build quantum machines that don't get lost in chaos but harness it.
The 'nine handshakes' between quantum computer states almost matches the six degrees of separation among people, discovered in the 1960s by psychologist Stanley Milgram, who sent letters through random acquaintances.