Schrödinger’s cat just got bigger: quantum physicists create largest ever ‘superposition’

In the iconic quantum double-slit experiment, a photon acts like a wave and interferes with itself — illustrating the mind-boggling concept that particles can exist in a ‘superposition’ of possible locations at once. But just how big can such a quantum object be? At least as big as a blob of around 7,000 sodium atoms, it turns out. Using a painstakingly constructed experimental set-up, researchers managed to observe tell-tale interference patterns for sodium clusters some 8 nanometres wide, with superpositions that stretched across 133 nanometres. The clusters are as big as some viruses, raising the tantalising possibility of putting biological matter through the same experimental set-up.

Blogger Comments:

This is an impressive and painstaking experiment. Demonstrating clear interference patterns for clusters of around 7,000 atoms, spatially separated by more than 100 nanometres, represents a real extension of the regimes in which quantum descriptions can be experimentally sustained. As experimental control of isolation, coherence, and interferometric precision, the work deserves genuine admiration.

What is worth handling carefully, however, is how such results are often presented.

When articles speak of objects “existing in a superposition of locations at once”, or frame the experiment as probing whether quantum mechanics “still applies” at larger scales, a subtle shift occurs. Formal features of a successful theoretical description begin to be treated as literal claims about what the system is, rather than about how it can be described under tightly controlled conditions.

From a more structural perspective, a superposition is not an ontological state of affairs. It is a theoretical potential: a space of possible outcomes defined relative to a particular experimental arrangement. The interferometer does not reveal a sodium cluster to be “in many places”; it actualises a phenomenon whose meaning is inseparable from the construal that makes it observable.

Seen this way, the familiar question — “where does the quantum world give way to the classical?” — is slightly misplaced. What changes is not the world itself, but the stability of the conditions under which certain descriptions remain coherent. Quantum mechanics does not abruptly fail at larger scales; rather, it becomes progressively harder to maintain the isolation and precision required for quantum descriptions to remain usable.

The real achievement of experiments like this is therefore not that they show ever-larger objects to be “really” quantum, but that they map how far we can extend a powerful theoretical construal before the practical conditions that sustain it dissolve.