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

Physicists can predict the jumps of Schrodinger's cat (and finally save it)
Yale researchers have found a way to catch and save Schrödinger's famous cat, the symbol of quantum superposition and unpredictability. Credit: Kat Stockton

Yale researchers have figured out how to catch and save Schrödinger's famous cat, the symbol of quantum superposition and unpredictability, by anticipating its jumps and acting in real time to save it from proverbial doom. In the process, they overturn years of cornerstone dogma in quantum physics.

The discovery enables researchers to set up an early warning system for imminent jumps of artificial atoms containing quantum information. A study announcing the discovery appears in the June 3 online edition of the journal Nature.

Schrödinger's cat is a well-known paradox used to illustrate the concept of superposition—the ability for two opposite states to exist simultaneously—and unpredictability in . 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 decays. The superposition theory of quantum physics suggests that until someone opens the box, the cat is both alive and dead, a superposition of states. Opening the box to observe the cat causes it to abruptly change its randomly, forcing it to be either dead or alive.

The quantum jump is the discrete (non-continuous) and random change in the state when it is observed.

The experiment, performed in the lab of Yale professor Michel Devoret and proposed by lead author Zlatko Minev, peers into the actual workings of a quantum jump for the first time. The results reveal a surprising finding that contradicts Danish physicist Niels Bohr's established view—the jumps are neither abrupt nor as random as previously thought.

For a tiny object such as an electron, molecule, or an artificial atom containing quantum information (known as a qubit), a quantum jump is the sudden transition from one of its discrete energy states to another. In developing quantum computers, researchers crucially must deal with the jumps of the qubits, which are the manifestations of errors in calculations.

The enigmatic quantum jumps were theorized by Bohr a century ago, but not observed until the 1980s, in .

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

"Despite that," added Minev, "We wanted to know if it would be possible to get an advance 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 the University of Auckland, a pioneer of quantum trajectory theory and a co-author of the study.

In addition to its fundamental impact, the discovery is a potential major advance in understanding and controlling . Researchers say reliably managing quantum data and correcting errors as they occur is a key challenge in the development of fully useful quantum computers.

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

Microwave radiation stirs the artificial atom as it is simultaneously being observed, resulting in quantum jumps. The tiny quantum signal of these jumps can be amplified without loss to room temperature. Here, their signal can be monitored in real time. This enabled the researchers to see a sudden absence of detection photons (photons emitted by an ancillary state of the atom excited by the microwaves); this tiny absence is the advance warning of a quantum jump.

"The beautiful effect displayed by this experiment is the increase of coherence during the jump, despite its observation," said Devoret. Added Minev, "You can leverage this to not only catch the jump, but also reverse it."

This is a crucial point, the researchers said. While quantum jumps appear discrete and random in the long run, reversing a quantum jump means the evolution of the state possesses, in part, a deterministic and not random character; the jump always occurs in the same, predictable manner from its random starting point.

"Quantum jumps of an atom are somewhat analogous to the eruption of a volcano," Minev said. "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.


Explore further

Extremely accurate measurements of atom states for quantum computing

More information: To catch and reverse a quantum jump mid-flight, Nature (2019). DOI: 10.1038/s41586-019-1287-z , https://www.nature.com/articles/s41586-019-1287-z
Journal information: Nature

Provided by Yale University
Citation: Physicists can predict the jumps of Schrodinger's cat (and finally save it) (2019, June 3) retrieved 19 June 2019 from https://phys.org/news/2019-06-physicists-schrodinger-cat.html
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Jun 03, 2019
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Jun 03, 2019
"The Yale team used a special approach to indirectly monitor a superconducting artificial atom, with three microwave generators..."

This cat suspected catch in the story and pounced on a rat at this text. We are talking here about orders of magnitude (and the EM version) in quantum scale over the nuclear forces that govern the decay of the sort of radionuclide that Schödinger had in mind. It wouldn't surprise me in the least that precursors to decoherence in such relatively h u g e systems might be detectable.
I would add to that the crucial element of pre-monitoring. Pre-monitoring is a class of monitoring. You may not look inside Schödinger box. You may not peek. You may not set up femtoscopic surveillance cameras to spy on the radium's nucleons and see if any are getting antsy. Even if you could.

Jun 03, 2019
So, is this really a Big Deal, or is it not? The article makes it sound like a major announcement, but then gives no real information about what happened and why it should rock our world.

Jun 03, 2019
If the quantum state or one of its properties is predictable then it is not in superposition but has some discrete state. Each subsequent discrete state can only be discrete if the previous state was discrete, predictability is based on discrete mechanisms or 'hidden variables' influencing the outcome.

What they appear to have discovered is that the condition they are investigating is either not in superposition or that there is some property that is not in superposition. The assumption that all of the properties of an event either are or are not in superposition is an arbitrary assumption given without evidence or theoretical foundation.

Jun 03, 2019
If the quantum state or one of its properties is predictable then it is not in superposition but has some discrete state. Each subsequent discrete state can only be discrete if the previous state was discrete, predictability is based on discrete mechanisms or 'hidden variables' influencing the outcome.

What they appear to have discovered is that the condition they are investigating is either not in superposition or that there is some property that is not in superposition.
The way I see it, they are using a system that is so large that it treads on the borderlines between quantum and classical scales. I don't think Schrödinger chose a   s u b   -atomic scale by whim, nor was it his intention to produce an amusing paradox, but to address EPR with a macroscopic, classical, system (cat) that is dependent on a full-on quantum system, best represented at the scale of an (unstable) nucleus.

Jun 04, 2019
So, is this really a Big Deal, or is it not? The article makes it sound like a major announcement, but then gives no real information about what happened and why it should rock our world.
You have to wait a month until people start saying this is going to win a Nobel like it was equal to the discovery of the Higgs Boson or something, or it looks like it going to wind up as just another footnote among dozens in the Wikipedia Schroedinger's Cat article.
However, it does sound like something that may wind up of practical use in quantum computing and quantum cryptography.

Jun 04, 2019
It looks like a catastrophe to me!

Jun 04, 2019
By reversing the process, can the original quantum state be returned to?

Jun 05, 2019
By reversing the process, can the original quantum state be returned to?
It's a good question. The answer is "no." The reason is because quantum states are not reversible. They'll come out random just like they do forward. The mechanics are reversible; the outcomes are not because they are probabilistic and therefore random, just as the original outcomes are.

Jun 10, 2019
Why are we still using QM? Ever try setting c=1; T=Lambda; q=+/-1? Juz an isometric mathematical space onto reality? Best if every point is a memory location, with memory as a programmable object. If yo understand stability; you know you can cut and paste a set of charges in ya simulators. Best with good programming. Let the computer figure it out. You don't need a cat unless it's NCA&T!

I like a unit less space to avoid errors in our Universal constants. Please take charge literally, its field is infinite and the character of the center is not different from its field; except when the center moves, the field is not immediately updated everywhere.

Jun 10, 2019
Notice the wake when a charge moves. It also creates a force we call magnetism. The attraction between sets we call Gravity. We might have too many words for snow. This might be where you're confused, nomenclature it's so cluttered!

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