Posted in | Quantum Physics

Yale Researchers Develop an Early Warning System for Quantum Jumps

Schrödinger’s famed cat is a popular paradox used to describe the concept of quantum superposition and unpredictability.

Yale researchers have found a way to catch and save Schrödinger's famous cat, the symbol of quantum superposition and unpredictability. (Image credit: Kat Stockton)

Now, Yale University researchers have identified a new way to catch and save this well-known paradox by predicting its jumps and workings in real time so as to save it from the familiar doom. In doing so, the researchers overturned years of central dogma in quantum physics.

This latest finding allows scientists to install an early warning system for forthcoming jumps of artificial atoms comprising of quantum data. A study reporting this discovery has been published in the June 3rd, 2019 online edition of the journal, Nature.

Schrödinger’s cat is a popular paradox used for demonstrating the theory of unpredictability and superposition—the capability of two opposite states to exist at the same time—in quantum physics. The concept is that a cat is placed in a closed box with a poison and a radioactive source that will be activated following the decay of an atom of the radioactive substance.

The superposition concept of quantum physics indicates that until the box is opened by someone, the cat is assumed to be both dead and alive—that is, a superposition of states. When the box is opened to observe the cat, the quantum state of the cat is rapidly altered in a random manner, pushing it to be either alive or dead.

The quantum jump can be defined as the random and discrete (non-continuous) transition in the state when it is observed.

The experiment, which was conducted in the laboratory of Michel Devoret, a Yale University professor, and suggested by lead author Zlatko Minev, looks into the real workings of a quantum jump for the very first time. The outcomes expose an unexpected finding that challenges the established view of Danish physicist Niels Bohr—that is, the jumps are neither random nor sudden as believed before.

For a small object like a molecule, electron, or an artificial atom containing quantum data (called qubit), a quantum jump is referred to the abrupt change from one of its distinct energy states to another. When building quantum computers, it is important that scientists deal with the qubits jumps, which are said to be the manifestations of mistakes in calculations.

Although Bohr theorized the inscrutable quantum jumps 100 years ago, this was not seen in atoms until the 1980s.

These jumps occur every time we measure a qubit. Quantum jumps are known to be unpredictable in the long run.

Michel Devoret, the F.W. Beinecke Professor of Applied Physics, Yale University

Devoret is also a member of the Yale Quantum Institute.

Despite that, we wanted to know if it would be possible to get an advance warning signal that a jump is about to occur imminently.

Zlatko Minev, Study Lead Author, Department of Applied Physics, Yale University

Minev observed that the experiment was motivated by a hypothetical prediction by Professor Howard Carmichael of the University of Auckland, an innovator of quantum trajectory theory and also the study’s co-author.

Apart from the underlying effect, the finding is a major promising advance in interpreting and controlling quantum data. According to researchers, consistently controlling quantum information and rectifying errors as they emerge is a major challenge when it comes to developing entirely useful quantum computers.

A unique approach was used by Yale researchers to indirectly track a superconducting artificial atom, with the atom being irradiated by three microwave generators. This atom is covered in an aluminum-based 3D cavity. Minev developed the doubly indirect monitoring technique for superconducting circuits; the method enables the team to view the atom with unparalleled efficiency.

The artificial atom is stirred by microwave radiation as the former is concurrently being observed, leading to quantum jumps. The small quantum signal of these jumps can be augmented without any loss in room temperature. Here, real-time monitoring of the signal of these jumps is possible. This allowed the team to observe an abrupt absence of detection photons (that is, photons produced by a secondary state of the atom activated by the microwaves); this small and sudden absence provides an advance warning of a quantum jump.

The beautiful effect displayed by this experiment is the increase of coherence during the jump, despite its observation.

Michel Devoret, the F.W. Beinecke Professor of Applied Physics, Yale University

You can leverage this to not only catch the jump, but also reverse it,” added Minev.

According to the team, this is an extremely major point. Quantum jumps seem haphazard and discrete in the long run, but reversing a quantum jump would imply that the evolution of the quantum state partly has a deterministic and not haphazard character; the jump invariably takes place in the same, predictable way from its arbitrary starting point.

Quantum jumps of an atom are somewhat analogous to the eruption of a volcano. They are completely unpredictable in the long term. Nonetheless, with the correct monitoring we can with certainty detect an advance warning of an imminent disaster and act on it before it has occurred.

Zlatko Minev, Study Lead Author, Department of Applied Physics, Yale University

Other co-authors of the study include Robert Schoelkopf, Shyam Shankar, Shantanu Mundhada, and Philip Reinhold, all from Yale University; Mazyar Mirrahimi from the French Institute for Research in Computer Science and Automation; and Ricardo Gutiérrez-Jáuregui from the University of Auckland.

The U.S. Army Research Office supported the study.

This novel study is the recent step in Yale University’s quantum research work. Yale University researchers are at the forefront of efforts to create the first fully viable quantum computers and have done groundbreaking work in quantum computing with superconducting circuits.

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