Physicists Unleash AI to Devise Unthinkable Experiments

by Charles Q. Choi, Scientific American

Quantum physics can fly in the face of human intuition—even that of a physicist such as Mario Krenn at the University of Vienna. This counterintuitive quality makes it difficult for researchers to design experiments to explore the field. Now, to avoid intuitive pitfalls, Krenn and his colleagues have devised a computer program to automatically design new quantum experiments that they would not have thought of themselves.

The way that all known particles behave can be explained with quantum physics. A major feature of this branch of physics is that the world becomes a vague, bizarre place at its very smallest levels. For example, atoms and other basic building blocks of the universe can exist in states of flux known as superpositions, meaning they can seemingly be located in two or more places at the same time, or spin in opposite directions simultaneously; and with the phenomenon of quantum entanglement, two or more objects can get connected such that what happens to one instantaneously affects whatever is linked to it, no matter how far apart they are in the universe.

The surreal nature of quantum physics can be hard to swallow, even for scientists. The most famous analogy for superposition, Schrödinger’s cat, which presents a cat that may be simultaneously alive and dead, was intended by physicist Erwin Schrödinger to highlight the absurdity of the concept of superposition, not to popularize it. In addition, Einstein famously rebelled against the concept of entanglement, calling it “spooky action at a distance.” Numerous experiments, however, have proved quantum physics’s stranger phenomena over the decades—for instance, Krenn’s advisor Anton Zeilinger helped set the current record distance for entanglement of 144 kilometers, from La Palma to Tenerife in the Canary Islands.

So, University of Vienna physicists led by Mario Krenn have developed a computer program that can automatically design new quantum experiments that were previously unthinkable. The basis of the MELVIN program’s creation was the difficulty Krenn and colleagues encountered in attempting to generate a form of entanglement where three entities shared three properties known as Greenberger-Horne-Zeilinger (GHZ) states. MELVIN uses common building blocks of quantum experiments such as mirrors and holograms and virtually configures them to find non-intuitive arrangements that meet whatever goals researchers desire, such as a specific quantum state.

Upon finding a working result, the software automatically simplifies the design and reports it to the researchers. “I started the program in the evening and by the next morning, after a few hundred thousand different trials, it found one correct solution [to the GHZ states problem],” Krenn reports. He says MELVIN incorporates experiential learning, so that “if it found one good solution, it stores the good solution and can use it for follow-up experiments.” Krenn’s team also determined MELVIN could take sets of entangled particles and revise them so they switched properties with one another in a cyclical manner, which could be helpful in nearly hack-proof quantum cryptography. Moreover, MELVIN arrived at unexpected solutions the researchers were unlikely to have thought up. Read the article