Quantum computing can be powered by liquid-like electrons

The field of quantum computing may have just received a coherence and error-proofing boost in the form of parafermions: clustered electrons that behave like liquids in a special state of matter. Scientists from Nanyang Technological University in Singapore (opens in new tab) have demonstrated experimental results that they expect to lead to parafermions when electrons are maintained at temperatures close to absolute zero (-273 degrees Celsius). The research achieved a breakthrough by demonstrating that there are conditions under which electrons can have strong interactions – something that scientists have until now only theorized.

The orderly movement of electrons results in what we know as electricity. However, even when the electrons are moving in this “ordered” pattern, they really aren’t. Because they are negatively charged, the electrons repel each other, tending to move individually and chaotically in different directions (like a gas) instead of as a cohesive whole. They are similar to disabled drivers: they may reach their destination with a few “bumps” along the way. But when electrons behave like a liquid, it’s similar to replacing damaged drivers with normal ones; drivers who know and respect each other’s limits, speed and direction to reduce conflicts and better reach their destination.

Of course, engines like these are the subject of much theoretical thought, but the existence of strong electronic interactions has at least now been experimentally proven.

When the electrons are made to act in what is known as a “Tomonaga-Luttinger spiral fluid”, there are fewer particle interactions and energy exchanges between them and the system. This, in turn, reduces the amount of systemic and environmental perturbations that so often cause errors and collapsed quantum states in quantum systems. Electrons that have previously been cooled to near absolute zero are also an essential element as they allow certain materials to achieve a superconducting state where electrons cross its surface without any electrical resistance, further reducing possible interference elements in the environment. The system, which is cooled to absolute zero (in the experiment, to 4.5 Kelvin or -269 degrees Celsius), forces the particles to slow down so that they become almost stationary.

Electrons (and their spin property) have been used as quantum programmable particles for some time. As such, improvements in electron control that result in less interference mean fewer errors and improved coherence, meaning longer lifetimes for the actual qubits that can store or process information. In fact, some quantum systems (such as IBM’s Quantum One and Quantum Two) already use superconducting qubits.

In this case, the scientists used an atom-thick graphene substrate on which they deposited atom-thick crystals of tungsten ditelluride: a nearly two-dimensional material known as a “quantum spin Hall insulator” that isolates gravity from the inside but contains electrons from the outside. After collecting the graphene/tungsten ditelluride substrate and cooling it to absolute zero, the research team placed it under a scanning tunneling microscope that lay just one nanometer from its surface: smaller than a strand of DNA and smaller than any transistor made ever (even when looking at those powering the latest best graphics cards).

When placed under the scanning tunneling microscope and cooled to absolute zero, the researchers noticed that the electrons in the graphene/tungsten substrate increased their repulsion. Their repulsion was so strong that the electrons were forced to move collectively due to the interaction between each electron’s repulsive field. The researchers recorded a Luttinger parameter ranging from 0.21 to 0.33. This parameter represents the strength of interactions between particles; when it reaches 1, the interactions are weakest.

“When the Luttinger parameter is less than 0.5, the interactions are strong and the electrons are forced into collective motion. This is the realm where parafermions are predicted to exist,” said Assistant Prof. Weber. “This is a really remarkable range of variation because the Luttinger parameter can only vary between 0 and 1,” he continued. “Control of the Luttinger parameter at such low values ​​has never been observed before in any spiral Tomonaga-Luttinger fluid.”

The team now plans to lower temperatures even further using NTU Singapore’s new Ultra-Low Vibration Laboratory, which was built earlier this year. The lab will allow experiments to be conducted at temperatures even lower than 150 millikelvin (mK) – even closer to absolute zero, which should allow researchers to see stronger repulsion between electrons and actually observe parafermion groups.

Interestingly, the researchers’ approach appears to be somewhat related to Microsoft’s own race to implement so-called topological qubits and their necessary (and still missing) Majorana modes.