Next ASML Quantum computer gets stuck with a wire

 

On November 9, IBM released the 433-bit superconducting quantum processor Osprey, achieving this goal from a full range of upgrades from refrigeration, electronic control equipment to cabling.

 

In terms of cabling, IBM used flexible ribbon cable to replace the previous coaxial cable. osprey's flexible ribbon cable is suitable for low-temperature environments. The cable's resistance and thermal resistance are specifically designed to help microwave signals flow without conducting excessive heat that could interfere with quantum bits.

 

Although IBM did not disclose its flexible ribbon cable from where, but it is not difficult to know the manufacturer, because the flexible ribbon cable for quantum computers can be produced by only one manufacturer - Delft Circuits, the Chinese "Delft Circuits "Delft Circuits.

 

01Founded by three non-quantum computing professionals

 

In a recent interview, Artem Nikitin, head of sales at Delft Circuits, revealed that "a third of our total revenue comes from quantum computing, and quantum computing was our first beachhead." But when the company was founded in 2016, none of the three founders was a quantum computing professional.

 

Sal Jua Bosman, the CEO, graduated from Eindhoven University of Technology in the Netherlands in 2005 with a bachelor's degree in industrial design, then went on to study at the University of Amsterdam, where he received his Master of Science in 2011. During this time he has had many jobs, including independent designer, founder of an IoT company (a failed start-up), and even a high school physics teacher.

 

Daan Kuitenbrouwer, COO, graduated with a master's degree from Delft University of Technology in 2016, where he served as president of Master Dispuut, the university's master's research association in applied physics, during his master's degree, and also worked as a teaching assistant in physics, mathematics and mechanical engineering, and participated in the founding of Delft Circuits after graduation, when Bosman was Bosman was working on his PhD in superconducting quantum circuits at Delft University of Technology (he later dropped out).

 

From left to right: Daan Kuitenbrouwer and Sal Jua Bosman

 

Chief Financial Officer Paulianne Brouwer, on the other hand, is a less experienced manager, as she has long worked as a freelancer.

 

According to Kuitenbrouwer, who was pursuing a master's degree in applied physics at the time, he met Bosman, who was working on quantum bits, through a mutual friend in Delft, Kuitenbrouwer had always had the idea of starting a business, and the quantum industry was a new field with more room for new projects. It just so happened that Bosman already had a great idea to start a business in the quantum field.

 

Before starting Delft Circuits, Bosman studied the general computer industry in depth. While working on his PhD at Delft University of Technology, he noticed that the way quantum computers are currently being built is quite different from that highly decentralized and efficient industry. While I was working on my PhD, quantum technology was booming in Delft, with all the major U.S. tech companies jumping to the top of the list," he says. But at the same time, it was also very amateurish. Everyone was trying to build a complete computer from scratch, and scientists were soldering things together themselves." One day Bosman saw his professor order a very expensive refrigeration machine with cables that the professor had assembled himself, and he knew: This is my business model.

 

As an industrial designer, "I believe in specialization. I'm always looking for something that everyone needs and that no one thinks is sexy, because then you have your market."

 

In 2016, Kuitenbrouwer joined a company Bosman had previously founded as an intern. Over time, that internship grew into the business Delft Circuits is now. But in their opinion, Delft Circuits wouldn't be what it is today without a third person, Paulianne Brouwer, on board. She is the business brain behind the company.

 

02Shaping the future of quantum bit wiring

 

Most quantum computers currently use quantum bits that can only operate at temperatures close to absolute zero (-273.15 degrees Celsius), a situation that ordinary cables cannot cope with, and cables for quantum computers must: transmit signals, but not heat.

 

In 2017, Kuitenbrouwer and BosmanSal obtained the first measurements of microwave signal transmission through a superconducting cable immersed in liquid helium, and presented them at the annual meeting of the American Physical Society that year.

 

Starting with the first proof of concept, they did several pilot projects, and many large technology companies started this work a few years ago, as I/O was the bottleneck to scale their systems. However, as the problem became quite difficult, many of them became customers of Delft Circuits.

 

For quantum computers with superconducting quantum bits or silicon spin quantum bits, the quantum bits need to be cooled to very low temperatures to maintain their quantum properties. Depending on the setup, each quantum bit requires two to five (usually about four) channels to input and output microwave signals to and from the quantum bit. The dilution cooler quickly fills up with so many channels.

 

In addition, it is difficult to cool to such low temperatures, meaning that at low temperatures, it ends up taking megawatts of energy to remove milliwatts of heat, and you want to do everything you can to avoid generating heat. However, ordinary coaxial cables conduct heat from the outside into a quantum computer; that's why superconductors that don't conduct heat at ultra-low temperatures need to be used. This solves the problem around thermal isolation, and then comes the integration of all these channels, which Delft Circuits does by using photolithography on a flexible substrate.

 

There are three functional requirements for the inputs and outputs: first, transmission of the signal from A to B through the cable. second, signal conditioning, which is filtering, amplifying or attenuating the signal. Third, the interface from the cable to the quantum bits or other functional components.

 

Currently, Delft Circuits has achieved good control of transmission and signal conditioning; as a next step, they are developing their own interface with a higher package density compared to conventional connectors, so that more quantum bits can be connected.

 

Finally, the main challenge was to manufacture the components on a large scale: Delft Circuits developed a ribbon cable that was only 100 microns wide but several meters long, a manufacturing process that did not yet exist. They did all this work in-house.

 

Delft Circuits has 150 square meters of in-house manufacturing and pilot production facilities at the Delft Quantum Campus. The lab has sophisticated manufacturing processes, including metal deposition, lithography, chemical processing, high-resolution inspection, etc., and is capable of fabricating multilayer superconducting circuits on flexible substrates. 2022 saw the expansion of a cable factory in Delft. They also have one of the largest research cleanrooms in Europe, called the Levene Hook Laboratory.

 

 

03From coaxial cables to flexible cables

 

Early quantum computer cabling used coaxial cables, which are common in the telecommunications industry, Kuitenbrouwer says, adding that coaxial cables work with several circular layers through which signals can be sent. This applies to the high-frequency signals used in quantum systems. The only problem is when we need a lot of cable, which makes it not very scalable. For example, if you want to use components to amplify or weaken the signal, you cannot integrate them into the cable.

 

These problems can be solved by using another type of cable. "Instead of using coaxial cable, Delft Circuits uses ribbon cable. This has several advantages. First, the cables are much smaller, allowing multiple cables to be used side-by-side, while meaning we can use multiple channels on each cable. In addition, we can integrate other components, such as filters, into the cable. This combination makes these cables more scalable and can be applied to quantum systems."

 

This is an important reason why IBM is using flexible cables instead of coaxial cables. The company said at the time of the release of the 433-bit quantum processor that the new flexible cabling increased line density by 70 percent and reduced the price per line by a factor of five. This cabling will also improve the reliability and maintainability of the system.

 

Coaxial cable (top) and flexible cable (bottom) in IBM quantum computers

 

Delft Circuits has developed an innovative quantum computer cable technology called Cri/oFlex. The product name Cri/oFlex stands for Cryogenic i/o which is flexible (flexible cryogenic i/o) and this flexible microwave cable has the following characteristics.

 

Reduced form factor and scalability as the number of quantum bits increases

Low thermal conductivity (<4μW per channel at 3K-0.7K)

Easy installation

Integrated signal attenuation and filtering

High durability

 

As shown in the figure below, the cable is made from a unique combination of polyimide and silver, resulting in an extremely thin ribbon line channel with high microwave performance and flexibility. "We are making flexible, microwave and cryogenic cables," says Bosman. A cable with all of these properties at once has never been done before."

 

Cri/oFlex 3 cable with SMA RF connectors

 

In addition, the cable integrates all filter components (low-pass filter, band-pass filter and attenuator) to overcome the traditional microwave engineering challenges in cryogenics. By integrating all the necessary components, potential failure points and installation time are reduced and setup robustness is improved.

 

Delft Circuits offers three different product families based on the same technology, but with different specifications and performance. These products are suitable for various types of applications, such as quantum computing, astrophysics, optics, instrumentation, etc.

 

 

1) Cri/oFlex 1

 

These ultra-flexible microwave I/O cables meet the requirements of scanning probe microscopes and other vibration sensitive instruments. These cryogenic RF cables are extremely thin and flexible, providing minimal vibration coupling while transmitting signals. the Cri/oFlex 1 series features microwave transmission lines as thin as 0.3 mm and as narrow as 1 mm.

 

2) Cri/oFlex 2

 

These single-channel microwave I/O cables are suitable for dense sample spaces in chillers. Their small size reduces the thermal load, thus allowing an increased number of microwave lines in the cryostat. The flexible RF cabling is based on a single waveguide and the phase stability is practically insensitive to vibration or bending. cri/oFlex technology remains highly flexible from room temperature to low temperature.

 

3) Cri/oFlex 3

 

The Cri/oFlex 3 series is the company's flagship product, designed for scalability. Using signal lines with distributed attenuation and integrated microwave signal conditioning, there is little need for additional microwave components. Due to its small size and low thermal load, the Cri/oFlex 3 supports a large number of signal lines and can be installed in dilution chillers. The flexible cable includes up to eight parallel channels with 1 mm spacing between channels and no microwave shunting between stages.

 

Cri/oFlex combines flexible cryogenic cables with standard RF connectors to provide interconnection solutions for single and multi-channel cables. For example, the Cri/oFlex 2X cable for controlling transmon quantum bits, see the following figure.

 

 

Delft Circuits is also using its Cri/oFlex 3 for superconducting nanowire single photon detector (SNSPD) arrays, a key link in the realization of quantum communication networks. In testing, Cri/oFlex 3 has shown comparable performance to semi-rigid coaxial cables, and with comparable performance, the flexible cable can take advantage of scalability.

 

Left: Flexible cable in SNSPD; Right: Performance comparison with coaxial cable

 

Delft Circuits reveals that the company has delivered hundreds of Cri/oFlex cabling solutions to more than fifty customers worldwide to date. delft Circuits is also a member of the Dutch quantum ecosystem IMPAQT, working with the other five companies pictured below to develop complete stacks for quantum computers. bosman has found what he calls "specialized market".

 

Quantum System Integration