cross-posted from: https://lemmygrad.ml/post/11178911

Archive link: https://archive.ph/6Iiag

Chinese researchers have unveiled a new rare earth alloy so cold and efficient it could upend decades of reliance on helium-3 and send shock waves through the global race for quantum computers or ultra-sensitive detectors.

A mini-fridge built with the alloy has achieved temperatures extremely close to absolute zero using no moving parts. And it comes at a time when the US Defence Advanced Research Projects Agency (DARPA) is actively hunting for exactly such a technology.

On January 27, DARPA issued an urgent call for proposals: develop a modular, helium-3-free cooling system for next-generation quantum and defence technologies.

Less than two weeks later, the Chinese scientists answered – with a paper published in Nature.

The alloy “has the potential for mass production. The joint team has recently successfully developed a pure metal refrigeration module based on this alloy material,” the Chinese Academy of Sciences (CAS) said on its website on February 13.

“This highly efficient cooling module could offer a stable, portable cooling source for quantum chips and support major space exploration projects with a self-reliant refrigeration system,” CAS added.

“It marks a ‘China solution’ that ends dependence on helium-3.”

In physics, the lowest possible temperature is 0 Kelvin, or minus 273.15 degrees Celsius (minus 459.67 degrees Fahrenheit), a state known as “absolute zero”.

As materials approach this temperature, they exhibit radically different properties: liquid helium loses friction, mercury becomes superconductive and much cutting-edge quantum research becomes possible.

Currently, achieving such extreme low temperature primarily relies on a technique called dilution refrigeration, which requires helium-3. This stable isotope of helium is an essential resource that China largely imports. Its main sources are linked to nuclear weapons programmes in the United States and Russia, as well as civilian nuclear power plants in Canada.

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According to a research paper published in the journal Nature on February 11, the team employed an entirely different solid-state cooling technique known as adiabatic demagnetisation refrigeration (ADR).

In simple terms, the process involves a magnetic alloy being first placed in an existing low-temperature environment. Applying a magnetic field forces the countless internal microscopic magnets to align uniformly, releasing heat that is carried away.

When the alloy is then isolated from the environment and the magnetic field is removed, the internal magnets return to a disordered state, a process that absorbs heat and further lowers the material’s own temperature.

A major hurdle in this process has been the poor thermal conductivity of traditional materials. While they could get cold themselves, they struggled to effectively cool the surrounding components.

The collaborative team from the Institute of Theoretical Physics and the Hefei Institutes of Physical Science under CAS, together with Shanghai Jiao Tong University, has discovered a new material, a rare earth compound called EuCo2Al9 (ECA). It possesses thermal conductivity similar to metal, allowing it to efficiently channel the cold outward.

“ADR using ECA has achieved a minimum temperature of 106 millikelvin, setting a new record for metallic materials. Also, at such extreme temperatures, its thermal conductivity is one to two orders of magnitude higher than traditional magnetic refrigeration materials, overcoming the key bottleneck of inefficiently extracting the cooling power,” according to the academy.

The ADR method, which eliminates the need for helium-3, is gaining traction in the academic world.

In 2024, Peking University built two “refrigerators” using this principle for quantum computing research, which have been operating stably for several months.

Lightweight portability is poised to be a key advantage of the ECA refrigeration module. This year’s Chinese government work report mentions the goal of “cultivating and developing the quantum technology industry”.

Currently, superconducting quantum computers require massive dilution refrigerators to cool their chips to sub-kelvin temperatures. In the future, a more portable refrigeration module like this could be instrumental in building smaller, more compact quantum computers.