Physicists Watched a Quantum Material Rebuild Itself Like Ice After Laser Blasts

We already have quantum computers, but they’re highly specialized, not particularly practical, and only cover a fraction of the performance potential that scientists think this technology could ultimately unlock.

Quantum materials can host several competing electronic states, and figuring out how those states form is a longstanding challenge – which brings us to a new study published in Nature Physics.

The study by an international team of researchers investigates how two charge density wave (CDW) phases can emerge and co-exist in the same material.

The researchers use these relatively simple phases of electron behavior as a model for understanding phase competition in more complex quantum materials, including those with superconductivity and magnetism.

“Just like superconductivity, charge density waves are a collective phenomena where electrons move together in certain ways,” says physicist Yifan Su, from MIT.

“The power of CDWs is that they are a much simpler form of matter compared to superconductivity. They offer a playground for fundamental understanding.”

For their experiment, the researchers chose the material erbium tritelluride, which is already known to have the capacity to simultaneously hold two CDW orders – essentially, different electron density patterns that affect the material’s behavior – that define two quantum phases.

Erbium tritelluride develops one dominant CDW below about –8 °C (18 °F). A second CDW appears below about −113 °C (–171 °F), running perpendicular to the first through the crystal, creating a ‘checkerboard’.

These competing, co-existing CDWs require those cold temperatures to appear, but they’re difficult to study in a normal, equilibrium state.

“The mechanism responsible for the emergence of this second phase has long been debated, and our approach provides a powerful new way to uncover the hidden physics behind phase transitions in quantum materials,” says physicist Nuh Gedik, from MIT.

To actually see what was going on, the team used a one-two punch of short, intense laser pulses.

The first pulse shook up the ‘checkerboard’ of criss-crossing electron phases, so that they would have to reform. The second pulse was used as a way of measuring the reconstruction of the CDWs.

While the first, dominant phase returned as the researchers expected – in a gradual and uniform way – the second phase was more unusual, coming back in isolated pockets that then spread through the material, similar to crystals of ice appearing as water freezes.

Essentially, the results suggest the two CDW phases form through fundamentally different mechanisms.

“One of the biggest questions in physics is why some materials host multiple phases while others do not,” says Gedik.

“And when multiple phases do exist, how do they interact? Do they reinforce one another, compete, or co-exist independently?”

If you’re not a physicist, the relevance might not be immediately apparent, but these phases are what make quantum materials so special – and potentially so useful. Knowing more about them could ultimately help us understand how to initiate and control them.

“In systems that are much more complex, like high-temperature superconductors, you see there are multiple phases – magnetism, superconductivity, charge density waves, and they all exist together,” says Gedik.

“One of the theories is that the way they interact with each other is key for their exotic properties. The lessons we learn here can be applied to much more complex materials.”

Future studies could analyze those more complex materials using the same laser-pulse approach used here, the researchers suggest, revealing more about how quantum materials develop their characteristics.

That could also be useful for electronics: Further down the line it might be possible to replace the silicon chips of conventional systems with different, superior materials, but only if we’re able to build and control them with very specific precision.

Related: Quantum Computers Just Passed a Test That Classical Computers Fundamentally Can’t

“People believe the cornerstone of replacing silicon lies in quantum materials that have multiple coexisting phases,” says physicist Alfred Zong, who co-led the study as an MIT graduate student and is now at Stanford University.

“Our experiment provides a very neat way to study these multiple phases.”

The research has been published in Nature Physics.