IBM researchers reveal the first ever ‘half-Möbius’ molecule, using quantum computing

IBM researchers reveal the first ever ‘half-Möbius’ molecule, using quantum computing

By Joseph Howlett edited by Lee Billings

Scientists have just created a new, strange type of molecule. It is made of a bunch of atoms bound together in a ring, like many other, simpler molecules. But if you could somehow zoom in on the electrons sliding around the atoms, you would see that their motion around the ring had become strange and convoluted. These twists form a new structure similar to the familiar mind-blowing one-sided, single-edge Möbius strip, but even more complicated.

The team, based at IBM Research, constructed this molecule by manipulating individual atomic bonds and then imaged it with high-powered microscopy. The researchers also confirmed what they saw with the power of IBM’s state-of-the-art quantum computers. Their work was published today in Science. It is the latest breakthrough in “topological” chemistry, the study of oddly shaped molecules and the bizarre quantum behavior they exhibit. And it shows how quantum computers can help study and simulate such subatomic chaos.

Until the new study, no one had even imagined this as a theoretical possibility – and now it is real. “The fact that such a molecule has not only been theoretically proposed but has actually been synthesized will have a major impact on the field of molecular science,” says Yasutomo Segawa, a researcher at the Institute for Molecular Science in Japan, who was not part of the team’s work.

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To build their aberrant molecule, the IBM team turned to a pastime. The same lab popularized atomic manipulation back in 2013, when researchers there assembled atoms into images to produce a stop-motion film called A boy and his atom. Using the same fine-tipped instruments they use to image and manipulate individual atoms, the new study’s researchers can break specific bonds and tear certain atoms from a molecule. They started with a more complicated molecule and carefully wrestled it into its “half-Möbius” shape.

To understand half-Möbius, it helps to start by imagining a “full Möbius” molecule. The atoms are arranged in a simple ring. The topology comes into play when you look at each atom’s electron cloud, which is made of two “lobes” that extend up and down and represent where you’re likely to find the atom’s electrons. Each atom’s lobe axis has an orientation that is different from its neighbors. As you go around the loop, the orientation of these axes wraps around so that the last atom’s lobes point almost upside down compared to the first.

If you trace out the path of all the atoms’ top lobes, it will be like an ant walking along a Möbius strip: after one cycle, the insect will land upside down from where it began its journey. After two, the ant will be back to the starting point.

This does not matter physically. If you turn an atom’s electron cloud upside down, it doesn’t actually change where you’re likely to find a given electron. But an electron that takes this hectic path and one that doesn’t can “interfere” noticeably, a bit like tuning into two conflicting radio signals on nearly identical channels.

Half-Möbius is even weirder. Here, the electron clouds are cross-shaped, which allows them to twist halfway instead of turning all the way around.

Instead of imagining a stripe, start with a cross-shaped loop. Cut it in one place.

Now turn it 90 degrees and glue it back together. You will end up with something like the image below.

An ant that starts at the top of the yellow band will only end up back at the starting point after four trips around the circle.

That ant’s trip is similar to an electron’s orbit around the half-Möbius molecule.

Electron clouds live deep in the quantum realm and are a challenge to image. Even with the best microscopes available, scientists could only resolve a hazy cloud.

To prove that this cloud was as convoluted as they hoped, they turned to a newer mainstay from IBM, the quantum computer. They used it to simulate the electrons rushing around the molecule they thought they had made and produced an image of what it would look like in their microscope. They then repeated the process for a simpler, untwisted version of the same molecule. With the two images to compare with their observation, it became clear that the molecule was indeed a half-Möbius.

It’s a strange kind of object that can only be put together with such a confluence of new technologies. “We made this freakish molecule under these very special conditions,” says Leo Gross, a member of the IBM team. “In nature, they would never be stable.”

The researchers are excited that IBM’s quantum computer is proving so useful in an actual discovery. They also simulated electrons with a regular, “classical” computer for comparison. But in this case quantum has its advantages.

The more electrons there are in the calculation, or the more quantum states you leave them in, the more elaborate the calculation – whether classical or quantum. But because IBM’s quantum computer represents the states using quantum bits, called qubits, which can represent a superposition of different quantum possibilities, it can perform larger calculations at lower cost.

So the team was able to scale up the calculation and confirm that, after a certain point, the resulting electron clouds looked more or less the same. Then the scientists could say with certainty that they understood the quantum mechanics of the images their microscopes had captured.

For Ivano Tavernelli, another of the team’s researchers, it is an example of how far quantum computing has come. “In about 10 years, we were able to go from two to four qubits up to 100,” he says. “If we can keep going like this, I think it would be fun.”