IBM's Goldeneye: Behind the scenes at the world's largest dilution refrigerator

Quantum computing relies on incredibly low temperatures. Meet IBM's subzero beast.



It's fitting that one of the coolest quantum computing projects going has an equally cool name. Goldeneye is IBM's internal codename for the world's largest dilution refrigerator, which will house a future 1,000,000 qubit quantum processor. 

In September 2020, IBM debuted a detailed roadmap about how it will scale its quantum technology in the next three years to reach the true quantum industry inflection point of Quantum Advantage -- the point at which quantum systems will be more powerful than today's conventional computing.  

But there's a catch: You can't do anything in quantum without incredibly low temperatures.

To reach this 'moon landing' moment, the IBM team developed the largest dilution refrigerator, which will house a future 1,000,000 qubit system. Work is underway to reach the goal of quantum computer capable of surpassing conventional machines by 2023, and this 10-foot-tall and 6-foot-wide "super-fridge" is a key ingredient, capable of reaching temperatures of 15 millikelvin, which is colder than outer space. The fridge gets so cold it takes between 5 and 14 days to cool down.

I caught up with Jerry Chow, Director of Quantum Hardware System Development for IBM, to learn about the Herculean project and to find out what's next for IBM's quantum computing ambitions.

Let's start with the basics: Why is a super-fridge necessary for useful quantum computing and what advances in the last decade or so have aided that effort?

Superconducting qubits need to be cooled down to between 10-15 millikelvin for their quantum behavior to emerge. They need to be kept that cold to ensure that their performance is high. Dilution refrigeration technology, which has been around for a really long time, is an enabling technology specifically for superconducting qubits for quantum computing. Whereas a different type of qubit might require its own unique set of hardware and infrastructure.

Around 2010, cryogen-free dilution refrigerators became en vogue. These didn't require transferring and refilling liquid cryogenic helium every other day to keep these refrigerators cold. In fact, my PhD at Yale was completed entirely at the time when we were still experimenting on what we call "wet" dilution refrigerators. However, around 2010, the whole world started switching over to these reliable cryogen-free "dry" dilution refrigerators which suddenly allowed for experiments with superconducting qubits to be done for a lot longer periods of time with no interruption. 

How did the Goldeneye project first took shape? And what were the biggest perceived technical challenges early on?

The very first thought of building something at that scale came from my colleague Pat Gumann while brainstorming long-term, 'crazy' ideas in my office in November of 2018. At that time, our team was tasked with deploying our first 53-qubit quantum computer in the IBM Quantum Computation Center in Poughkeepsie, NY, a challenge which pushed a few limits in what we could place into a single cryogenic refrigerator at the time. While working on it, it also really made us start thinking beyond, and almost instantly that we will need much larger cryogenic support system to ever cool down between 1,000 to 1 million qubits. This was simply due to the sheer volume required to host, not only all the qubits, but also all of the auxiliary, cryogenic, microwave electronics – cables, filters, attenuators, isolators, amplifiers, etc.

It became very apparent that a new way of thinking in terms of the design would be needed and we started coming up with different form factors for how to effectively construct and cool down a behemoth such as the super-fridge. Some of the challenges we had were purely infrastructural such as how were we going to find a space in the building big enough to start this project and where would we find the capabilities to work with really large pieces of metal.

And as the rubber started to meet the road what have turned out to be the biggest hurdles to creating a useful quantum computer, and what does that say about the trajectory of the technology?

Some of the most challenging hurdles to overcome includes improving the quality of the underlying qubits, which includes improving the underlying coherence times (the amount of time that qubits stay in a superposition state), the achievable two-qubit gate fidelities, and reducing crosstalk between qubits as we scale up.

For that matter, most of these improvements feed into an overall quality measure for the performance of a quantum computer which we have defined called the Quantum Volume. Having a measure such as Quantum Volume allows us to really show progression along a roadmap of improvements, and we have been demonstrating this scaling of Quantum Volume year over year as we make new systems better and better.

The higher the Quantum Volume, the more real-world, complex problems quantum computers can potentially solve. A variety of factors determine Quantum Volume, including the number of qubits, connectivity, and coherence time, plus accounting for gate and measurement errors, device cross talk, and circuit software compiler efficiency.

Where is IBM right now with regards to Goldeneye? What can we expect in the near future?

Our "Goldeneye" super-fridge is very much an ongoing project, which is on target for completion in 2023. It is just one critical part of our long-term roadmap for scaling quantum technology. As we continue to execute on the roadmap we announced in September, we're pleased to share that we achieved a Quantum Volume of 128 in November and we're working towards improving the quality of our underlying systems in order to debut our 127-qubit IBM Quantum Eagle processor later this year.

In the near future, we're poised to make exciting developments with our entire technology stack, including software and control systems. At IBM, we're working toward a complete set of broad innovations and breakthroughs. 

What will quantum computing mean for the world in the long run? How will be a game changer?

Quantum computing will vastly broaden the types of problems we will address, and the technology offers a new form of computation that we expect to work in a frictionless fashion with today's classical computers. From the chemistry of new materials, and the optimization of everything from vehicle routing to financial portfolios, to improving machine learning, quantum will be an integral part of the future of computing and we're proud to be laying the foundation for a future of discovery.

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