Based on a double-differential measurement of the spin density matrix for top quark-antiquark pairs, carried out by the CMS collaboration in the helicity and beam bases, a set of quantum observables was calculated: discord, steerability, Bell correlations, and magic. Discord was detected with a significance exceeding 5σ in several regions of phase space, including for separable states. For the first time in high-energy physics, evidence for steerability was obtained at a level above 3σ. Bell correlations are absent in the studied region, which agrees with theory. The results experimentally confirm the hierarchy of quantum correlations: the basic form is discord, followed by entanglement, steerability, and finally Bell correlations. The significance of non-zero magic — an additional quantumness characteristic — also exceeds 5σ in a number of regions.
At the Large Hadron Collider, by accelerating particles to nearly light speeds, top quarks are created — the heaviest building blocks of the Standard Model. They live for vanishingly small fractions of a second but manage to exhibit complex quantum connections.
These connections are like levels of dance synchronization. Discord is when two people move in a common rhythm but each on their own (here, entropy, a measure of disorder, is useful). With entanglement, which Erwin Schrödinger considered the essence of the quantum world, one partner instantly responds to the other's movements. Steerability is the ability of a leader to dictate the steps to a follower. And perfect harmony, like in a rehearsed ballet, is Bell correlation, named after John Stewart Bell.
CMS detected discord and steerability in top quarks but did not find Bell correlations. The surprise was 'quantum magic' — a state where quantum properties are so non-classical that they cannot be reproduced on ordinary computers.
🎯 The top quark is nearly 200 times more massive than the proton and vanishes faster than a trillionth of a second. In that brief moment, it exhibits the most complex quantum connections.
🎬 In 'The Quantum Thief,' quantum correlations are used for faster-than-light communication; the real experiment shows that connections are even more diverse — from discord to quantum magic — opening up room for imagination.