AND GOD SAW THE LIGHT:

It is the most fundamental, and yet also the strangest postulate of the theory of quantum mechanics: the idea that a quantum system will catastrophically collapse from a blend of several possible quantum states to just one the moment it is measured by an experimentalist.

In textbooks on quantum mechanics, the collapse is depicted as sudden and irreversible. It is also extremely counterintuitive. Researchers have struggled to understand how a measurement can profoundly alter the state that an object is in, rather than just allowing us to learn about an objective reality.

A new experiment1sheds some light on this question through the use of weak measurements -- indirect probes of quantum systems that tweak a wavefunction slightly while providing partial information about its state, avoiding a sudden collapse.

Atomic and solid-state physicist Kater Murch of the University of California, Berkeley, and his colleagues performed a series of weak measurements on a superconducting circuit that was in a superposition -- a combination of two quantum states. They did this by monitoring microwaves that had passed through a box containing the circuit, based on the fact that the circuit's electrical oscillations alter the state of the microwaves as they pass through the box. Over a couple of microseconds, those weak measurements captured snapshots of the state of the circuit as it gradually changed from a superposition to just one of the states within that superposition -- as if charting the collapse of a quantum wavefunction in slow motion.

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