Particle physics is as necessary to explain the atomic world as it is incomprehensible. One of its biggest mysteries is, for example, how particles can apparently exist in two states at once (a quantum leap).
A group of researchers has set up an early warning system to anticipate the imminent jumps of artificial atoms that contain quantum information. And by the way, years of fundamental theory of quantum physics fly by with a stroke of the pen.
Translated to the classic academic example of Schrödinger’s paradox, it could be said that scientists have managed to save the cat from its uncertain end. Let’s review what the paradox says before continuing.
Schrödinger’s paradox
Schrödinger’s cat is a well-known paradox that is used to illustrate the concept of superposition, the ability for two opposite states to exist simultaneously, and unpredictability in quantum physics.
The idea is that a cat is placed in a box sealed with a radioactive source and a poison that will be activated if an atom of the radioactive substance decays. The superposition theory of quantum physics suggests that until someone opens the box, the cat is alive and dead at the same time – a superposition of states. Opening the box to observe the cat causes it to abruptly change its quantum state at random, forcing it to be dead or alive.
The new experiment, carried out in the laboratory of Yale professor Michel Devoret and proposed by the study’s lead author Zlatko Minev, resembles the actual operation of a quantum leap for the first time. The results reveal a surprising finding that contradicts the established opinion of Danish physicist Niels Bohr; the jumps are not abrupt or as random, as previously thought.
Enigmatic quantum jumps were theorized by Bohr a century ago, but were not observed until the 1980s, in atoms.
As the researchers put it: “Quantum jumps are known to be unpredictable in the long term. Despite that, Minev added, “we wanted to know if it would be possible to get an early warning signal that a jump is imminently about to occur.”
The Yale team used a special approach to indirectly monitor a superconducting artificial atom , with three microwave generators radiating the atom encased in a 3D cavity made of aluminum. The doubly indirect monitoring method, developed by Minev for superconducting circuits, enables researchers to observe the atom with unprecedented efficiency.
Microwave radiation shakes the artificial atom as it is observed simultaneously, resulting in quantum jumps. The small quantum signal from these jumps can be amplified without losing room temperature. Here, your signal can be monitored in real time. This allowed the researchers to see a sudden absence of detection photons (photons emitted by an auxiliary state of the atom excited by microwaves); this small absence is the early warning of a quantum leap.
“The beautiful effect shown by this experiment is the increased coherence during the jump, despite your observation,” Devoret explains. Minev added: “We can take advantage of this to not only catch the jump, but also reverse it.”
While quantum jumps are shown to be discrete and random in the long run, reversing a quantum jump means that the evolution of the quantum state has, in part, a deterministic and non-random character ; the jump always occurs in the same predictable way from its random starting point.
What is the use of anticipating a quantum leap?
For a small object such as an electron, a molecule, or an artificial atom that contains quantum information (known as a qubit ), a quantum leap is the sudden transition from one of its energy states to another. In the development of quantum computers , researchers have to deal with jumps in qubits , which are the manifestations of errors in calculations.
“These jumps occur every time we measure a qubit, ” according to Devoret, the FW Beinecke Professor of Physics and Applied Physics at Yale and a member of the Yale Quantum Institute.
In addition to its fundamental impact, the discovery is a potential breakthrough in understanding and controlling quantum information. The researchers say that reliably managing quantum data and correcting errors as they occur is a key challenge in developing fully useful quantum computers.
The quantum jumps of an atom are somewhat analogous to the eruption of a volcano. They are completely unpredictable in the long run. However, with proper monitoring, scientists could with certainty detect an early warning of impending disaster and act on it before it has occurred.
The study announcing the discovery appears online June 3 in the journal Nature.
Z. K. Minev, S. O. Mundhada, S. Shankar, P. Reinhold, R. Gutiérrez-Jáuregui, R. J. Schoelkopf, M. Mirrahimi, H. J. Carmichael, M. H. Devoret. ‘To catch and reverse a quantum jump mid-flight’. Nature, 2019; DOI: 10.1038 / s41586-019-1287-z
