To catch a quantum jump

Is it possible to know if a quantum jump is about to occur? Researchers have been asking themselves this question for a long time, and the answer is a resounding “yes”, according to a new study by a team at Yale University in the US. As well as being of great importance for fundamental physics studies, the result, obtained by measuring the flight of a superconducting artificial three-level atom when it is excited by a beam of microwaves, might even be useful for correcting errors in quantum computing in the future.

It was Niels Bohr in 1913 who first put forward the concept of quantum jumps, which are the sudden transitions of a tiny object (such as an electron, molecule, or atom) from one of its discrete energy states to another. However, many of his peers at the time – including Erwin Schrödinger – strongly objected to their existence, instead postulating instead that they are not instantaneous.

Researchers didn’t actually observe quantum jumps until 1986 (in individual atoms). Since then, they have seen them in various atomic and solid-state systems and have shown that they are an essential phenomenon in processes such as quantum feedback control, and in particular for detecting and correcting quantum errors caused by decoherence in quantum information systems. Quantum error correction is a key challenge in the development of fully-functioning, real-world quantum computers.

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