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Study Shows Ways to Bring Several Molecules into Single Quantum State, at Once

Scientists have envisioned great ideas for the potential of quantum technology, ranging from earthquake sensors to unhackable networks.

Prof. Cheng Chin in his laboratory at the University of Chicago, where his lab announced a breakthrough in bringing multiple molecules at once into a single quantum state—one of the most important goals in quantum physics. Image Credit: Jason Smith.

However, all these rely on a crucial technological feat—the ability to develop and control quantum particle systems, which are one of the smallest objects in the universe.

This aim is now a step closer, with the development of a new technique by researchers from the University of Chicago. The paper was published on April 28th, 2021, in the Nature journal and demonstrates how to transfer several molecules into a single quantum state at once, which is one of the most significant goals in the field of quantum physics.

People have been trying to do this for decades, so we’re very excited,” explained Cheng Chin, senior author of the study and a professor of physics at UChicago. Chin added that he had intended to realize this aim ever since he was a graduate student in the 1990s. “I hope this can open new fields in many-body quantum chemistry. There’s evidence that there are a lot of discoveries waiting out there.”

A Bose-Einstein condensate is one of the essential states of matter, where a group of particles cooled to almost absolute zero shares a quantum state and the entire group starts acting as if it were a single atom. It is somewhat like coaxing a whole band to march completely in step while playing in tune. Although this is hard to realize, when it happens, a completely new realm of possibilities can open up.

For a few decades, researchers have been able to perform this using atoms but what they would actually want to do is to perform this with molecules. An innovation such as this could form the basis of several forms of quantum technology.

However, since molecules are larger compared to atoms and include much more moving parts, a majority of the efforts to tap them have ended up in chaos.

Atoms are simple spherical objects, whereas molecules can vibrate, rotate, carry small magnets. Because molecules can do so many different things, it makes them more useful, and at the same time much harder to control.

Cheng Chin, Study Senior Author and Professor of Physics, University of Chicago

Chin’s team intended to leverage some new capabilities in the lab that had become available recently. Last year, they started experimenting with the addition of two conditions.

The first one was to further cool the entire system—down to 10 nanoKelvins, a split hair above absolute zero. They then loaded the molecules into a crawl space to pin them flat.

Typically, molecules want to move in all directions, and if you allow that, they are much less stable. We confined the molecules so that they are on a 2D surface and can only move in two directions.

Cheng Chin, Study Senior Author and Professor of Physics, University of Chicago

The outcome was a set of almost identical molecules—lined up with precisely the same vibrational frequency, the same orientation, and in the same quantum state.

The researchers noted that this molecular condensate is similar to a pristine sheet of new drawing paper for quantum engineering. “It’s the absolute ideal starting point,” added Chin. “For example, if you want to build quantum systems to hold information, you need a clean slate to write on before you can format and store that information.”

To date, they could connect up to a few thousand molecules together in such a state, and have started to investigate its potential.

In the traditional way to think about chemistry, you think about a few atoms and molecules colliding and forming a new molecule. But in the quantum regime, all molecules act together, in collective behavior. This opens a whole new way to explore how molecules can all react together to become a new kind of molecule.

Cheng Chin, Study Senior Author and Professor of Physics, University of Chicago

This has been a goal of mine since I was a student,” he added, “so we’re very, very happy about this result.”

Journal Reference:

Zhang, Z., et al. (2021) Transition from an atomic to a molecular Bose–Einstein condensate. Nature.

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