An orchestra where every musician plays their own part, yet together they weave a complex melody: that's what a cloud of atoms looks like when their spins (intrinsic rotations, like tiny tops) oscillate in sync. Usually, these tops behave independently. But place them between two mirrors and shine light on them, and something remarkable happens: light and atoms begin to 'sing' in unison, becoming entangled with each other.
In the new work, physicists showed how a Schrödinger's cat state emerges in such an ensemble — a quantum object that is both alive and dead, existing in a superposition of two opposite states. Only here, the 'cat' is not one but consists of thousands of atoms. Their spins point both up and down simultaneously. The key to success is operating near the superradiant phase transition: it's as if the orchestra suddenly played so loudly and cohesively that the sound burst far beyond the concert hall. At that moment, the system becomes ultrasensitive. Even a weak measurement, counting the photons that leak out of the cavity, allows you to 'cut out' the desired state from the overall chorus.
The authors performed numerical simulations and analytical calculations, confirming that this method works. Moreover, they found a connection to the well-known 'photon subtraction' procedure in optics: there, too, one obtains cats, but for single light beams. Here, the role of photons is played by collective excitations of the entire atomic cloud. This is not just a pretty analogy: it points to a deep kinship between quantum optics and many-body physics.
Such an approach could become the foundation for new quantum technologies, where information is encoded not in individual particles but in entire ensembles that are robust against noise. And who knows, maybe one day these 'orchestras' will play in quantum computers or ultra-precise sensors, with light itself as the conductor.
A 'Schrödinger's cat' state for a single atom is exotic, but for a cloud of thousands of atoms it's almost routine: such objects live longer and are easier to control because collective effects protect the quantum superposition from decoherence.
In Hannu Rajaniemi's novel 'The Quantum Thief', collective quantum states are used to store consciousnesses — similar 'cats' made of many particles could become the ideal memory cells of the far future.