Physicists can predict Schrodinger's cat jumps (and finally save it)

Yale researchers have discovered how to capture and save the famous Schrödinger cat, symbol of quantum superposition and unpredictability, anticipating its jumps and acting in real time to save it from disaster. In doing so, they are overturning years of fundamental dogma in quantum physics.

This discovery allows researchers to set up a rapid alert system for imminent jumps of artificial atoms containing quantum information. A study announcing the discovery appears in the online edition of the newspaper of June 3 Nature.

Schrödinger's cat is a well-known paradox used to illustrate the concept of superposition – the ability of the simultaneous existence of two opposite states – and unpredictability in quantum physics. The idea is that a cat is placed in a sealed box with a radioactive source and a poison that will be triggered if an atom of the radioactive substance disintegrates. The theory of superimpositions of quantum physics suggests that until someone opens the box, the cat is both alive and dead, a superposition of states. By opening the box to observe the cat, it abruptly changes its quantum state abruptly, forcing it to be dead or alive.

Quantum leap is the discrete (non-continuous) and random change of state when it is observed.

The experiment, carried out in the laboratory of Professor Michel Devoret at Yale and proposed by lead author Zlatko Minev, examines for the first time the actual functioning of a quantum leap. The results reveal a surprising discovery that contradicts the established vision of Danish physicist Niels Bohr: the jumps are neither abrupt nor as random as previously thought.

For a tiny object such as an electron, an artificial molecule or atom containing quantum information (known as qubit), a quantum leap is the sudden transition from one of its states to a quantum leap. discrete energy to another. In the development of quantum computing, researchers absolutely must deal with the jumps of qubits, which are the manifestation of computational errors.

Enigmatic quantum leaps were theorized by Bohr a century ago, but were only observed in the 1980s, in atoms.

"These jumps occur every time we measure a qubit," said Devoret, Professor of Applied Physics and Physics F.W. Beinecke at Yale and a member of the Yale Quantum Institute. "Quantum jumps are known to be unpredictable in the long run."

"Despite this," added Minev, "we wanted to know if it would be possible to receive a warning signal that a jump is about to occur imminently."

Minev noted that the experiment was inspired by a theoretical prediction by Professor Howard Carmichael of Auckland University, pioneering quantum trajectory theory and co-author of the theory of quantum trajectory. ;study.

In addition to its fundamental impact, discovery is a potential major advance in the understanding and control of quantum information. Researchers say that reliable management of quantum data and error correction as it occurs is a major challenge for the development of fully useful quantum computers.

Yale's team used a special approach to indirectly monitor a superconducting artificial atom, with three microwave generators radiating the atom enclosed in a 3D aluminum cavity. The doubly indirect monitoring method developed by Minev for superconducting circuits allows researchers to observe the atom with unprecedented efficiency.

Microwave radiation agitates the artificial atom observed simultaneously, resulting in quantum leaps. The tiny quantum signal of these jumps can be amplified without loss of ambient temperature. Here, their signal can be monitored in real time. This allowed the researchers to note a sudden absence of detection photons (photons emitted by an auxiliary state of the atom excited by microwaves); this tiny absence is the preliminary warning of a quantum leap.

"The nice effect demonstrated by this experiment is the increase in consistency during the jump, despite its observation," said Devoret. Minev added: "You can take advantage of it to not only grab the jump, but also reverse it."

This is a crucial point, the researchers said. While quantum jumps seem discrete and random in the long run, reversing a quantum leap means that the evolution of the quantum state has, in part, a deterministic and nonrandom character; the jump always occurs in the same predictable way from its random starting point.

"The quantum leaps of an atom are somewhat analogous to the eruption of a volcano," said Minev. "They are completely unpredictable in the long run, but with proper monitoring, we can definitely detect a warning of an imminent disaster and act before it happens.