Thursday, June 1, 2023

IBM has built the world’s largest, coldest fridge for cooling quantum experiments

The super-fridge is a proof-of-concept for a dilution refrigerator.

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Studying the coldest, furthest, lowest, and highest energies and the smallest things in the universe is difficult. It requires building all-new apparatuses that push the limits of modern technology.

Now, IBM has built the world’s largest dilution refrigerator- internally known as project Goldeneye- capable of cooling future generations of quantum experiments. This “super-fridge,” a dilution refrigerator larger than any commercially available today- by experimental volume.

As reported in IBM’s official blog, “The super-fridge contains 1.7 cubic meters’ worth of experimental volume, meaning it can cool a volume larger than three home kitchen refrigerators to temperatures colder than the outer space, versus previous fridges, which are in the range of 0.4-0.7 cubic meters.”

“These temperatures are required for performing state-of-the-art physics experiments and potentially running large quantum processors.”

During experiments, scientists cooled it to operating temperature (~25 mK) and wired a quantum processor inside.

How they built the world’s largest, coldest fridge?

Dilution refrigerators are experimental cryogenic devices that use a mixture of helium-3 (He-3) and helium-4 to cool a space volume to the milli-Kelvin (mK) regime (He-4).

Dilution refrigerators carry out this cooling by first employing a series of procedures to remove heat from the helium isotope mixture and then using vacuum pumps to circulate and dilute He-3 into the He-3/He-4 mix until the desired temperature is attained.

Until recently, all dilution refrigerators were “wet” systems, requiring already-cold substances like liquid nitrogen and other cryogenic fluids to begin the cooling.

Project Goldeneye features an all-new construction of the frame and cryostat — the main, barrel-shaped component responsible for the cooling — to maximize experimental volume while reducing noise and achieving the temperatures required.

world’s largest, coldest fridge
L: Interior of Goldeneye experimental superfridge. R: IBM Quantum’s Goldeneye team.

The cryostat also has a clamshell design, which enables the exterior vacuum chamber to open horizontally and eliminates the requirement for removing the whole external shell to reach the inside components.

A specially designed jib crane within the system could one day allow even a single person to run the fridge. Plus, it can be monitored remotely with the help of an open-source visualization platform.

Five “normal” units on top and five “inverted” units on the bottom of the cryostat’s interior can be installed as ten internal plates for attaching components in its top and bottom halves. Additionally, it may accommodate up to six separate dilution refrigerator units, allowing for chilling capacities of over 24 W at 4 K and up to 10 mW at 100 mK temperatures. Finally, the system’s weight of 6.7 metric tonnes reduces the need for additional dampening methods by helping to dampen vibrations.

Scientists noted“Most importantly, it works. After just three years from project inception to our recent 25 mK milestone, we performed one final characterization exercise: we put a qubit chip inside.”

“We could reproduce coherence times of around 450 microseconds, similar to those measured on other commercial dilution refrigeration systems. We did not observe a decrease in the qubit’s performance despite the different internal environment and much larger experimental volume.”

Despite being the largest, the super-fridge requires less space than present-day, large-scale dilution refrigerators.

Goldeneye will soon move to IBM Quantum Computation Center in Poughkeepsie, NY, where the team will be exploring large-scale cryogenic systems to develop the cooling needs of tomorrow’s quantum data centers, such as the Blues Kide platform under development for use with IBM Quantum System Two.

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