Flexible Cryogenic Cables Simplify Quantum Computer Design
Article By : Maurizio Di Paolo Emilio
Cryogenic cables could be the key to simplifying quantum computer design.
Delft Circuits announced its inclusion in the BICEP project in Antarctica, supporting NASA’s Jet Propulsion Laboratory (JPL) at the California Institute of Technology and other project partners. The team at JPL determined that advanced cables made by Delft Circuits will be installed in the telescope’s cryostat, as part of its new camera.
The JPL team will also replace the telescope’s sensors with new thermal kinetic inductance detectors (TKIDs), which are superconductive detectors leveraging the properties of quantum mechanics. The infrastructure requirements are extremely similar to what is required to set up and measure qubits in a quantum system.
In recent years, we have witnessed a growing interest from large multinational groups, researchers, and startups in quantum computing. Current supercomputers, also known as high-performance computing (HPC) systems, with high computational capacity are not yet able to solve problems above a certain level of complexity.
The quantum computing approach, on the other hand, promises to overcome current HPC limitations by exploiting a computing power that becomes higher the more qubits a system uses.
Quantum computer design challenges
The creation of a quantum computer involves unprecedented design challenges because of the need to keep individual qubits as stable as possible and unalterable by external agents. Depending on the type of technology used to implement the qubits, this often requires generating temperatures close to absolute zero to reduce noise as much as possible. As a result, quantum computing hardware is usually placed inside a cryogenic dilution refrigerator.
The challenge then becomes interfacing the low-temperature quantum device with the control electronics that normally operate at room temperature. This process requires highly complex wiring, considering that next-generation quantum processors will be able to incorporate more than a thousand qubits.
Figure 1 below shows the detail of a quantum computer and highlights some of the complex wiring involved in quantum computer design. While a normal coaxial cable could be sufficient to address and read a few dozen qubits (at the expense of a non-negligible encumbrance), the need remains for higher density interconnections—both from a physical dimension perspective and the need to reduce conduction heat in the dilution refrigerator.
Delft Circuits’ solutions
Founded in 2017 and headquartered in Delft, Netherlands, Delft Circuits has developed an innovative quantum computer cable technology called Cri/oFlex. Initially created to solve connection issues in quantum computer prototypes created as part of university research, this technology aims to create the perfect wiring for quantum computing. The result is a flexible microwave cable with the following characteristics:
- Reduced form factor and scalable as the number of qubits grows
- Low thermal conductivity (heat load of < 4 μW per channel @ 3K – 0.7K)
- Ease of installation
- Integrated signal attenuation and filtering
- High durability
Cri/oFlex combines flexible cryogenic cables with standard RF connectors to produce an interconnect solution that offers both single and multi-channel cables.
“We want to be the best quantum hardware supplier for specific parts of the value chain in the quantum industry,” said Sal Jua Bosman, CEO and co-founder of Delft Circuits, and Artem Nikitin, head of sales at Delft Circuits, during an interview with EE Times. “We mostly focus on input/output systems, and this ranges from sensors, to computers, to biomedical sensing—there’s a wide variety of applications.”
The cable, as shown in Figure 2, is created by using a unique combination of polyimide and silver, obtaining extremely thin stripline channels with high microwave performance and flexibility.
“What we are making are flexible, microwave, and cryogenic cabling. A cable with all these properties at once has never been done before,” Nikitin and Bosman said.
Bosman added, “You can always have microwave cables, but they’re rigid, or you can have flexible cables, but they’re for DC signals. And cryogenic is something on top of that.”
Moreover, the cable integrates all filtering components (low-pass filters, band-pass filters, and attenuators) to overcome traditional microwave engineering challenges in cryogenics. By integrating all required components, you can reduce potential points-of-failure and installation time, as well as increase the robustness of the setup.
The Cri/oFlex product family
Delft Circuits offers three different product families based on the same technology, but with different specifications and performance capabilities. These products address various types of applications, such quantum computing, astrophysics, optics, instrumentation and more.
These ultra-flexible microwave I/O cables meet the requirements of scanning probe microscopes and other vibration sensitive instruments. These cryogenic RF cables are very thin and flexible, enabling the transmission of signals while providing extremely minimal vibrational coupling. As such, the Cri/oFlex 1 series features microwave transmission lines as thin as 0.3 mm, and as narrow as 1 mm.
These single channel microwave I/O cables are suitable for densely packed sample spaces in refrigerators. They are small in size and reduce thermal loads, allowing for an increased number of microwave lines in cryostats. The flexible RF cabling is based on monolithic waveguides, and the phase stability is practically insensitive to vibrations or bending. The Cri/oFlex technology remains highly flexible, from room temperature down to cryogenic temperatures.
The Cri/oFlex 3 series is the company’s flagship product, specifically designed for scalability. It uses signal lines with distributed attenuation and integrated microwave signal conditioning, almost eliminating the need for additional microwave components.
Due to its small volume and low thermal load, Cri/oFlex 3 supports a high number of signal lines that can be installed inside a dilution refrigerator. The flexible cable includes up to eight parallel channels, with 1-mm inter-channel pitch and no microwave breakout between stages.
Cri/oFlex use cases
Many of Delft Circuits’ customers use microwaves at low temperatures. Among these customers is NASA’s JPL, where the research team uses astrophysics detectors to measure microwave background radiation from space.
“To detect this radiation, they need sensitive microwave kinetic inductance detectors (MKIDs), and they use our cable solutions to read out the signals,” Nikitin and Bosman said.
MKID devices couple with microwave-frequency resonators to provide a high level of multiplexing. This makes it possible to read out up to 1,000 detector pixels utilizing a single MKID cable and a microwave transmission measurement. To enable high-resolution imaging, such detector arrays are currently being expanded up to tens of thousands of pixels.
These detector chips need specially made cryostats with constrained space and cooling capacity because they are typically installed at the bottom of telescopes. Given the current trends in scaling up such detector arrays, there is a need for MKID microwave cabling that is both small and simple to install and has a low heat load.
“One-third of our total revenues come from quantum computing,” Nikitin and Bosman said. “Even though quantum computing is our first beachhead, we are thinking about other fields of application for our products, like astrophysics, which is very close to space applications, STM and AFM, and biomedical imaging.”
This article was originally published on EE Times.
Maurizio Di Paolo Emilio has a Ph.D. in Physics and is a Telecommunications Engineer. He has worked on various international projects in the field of gravitational waves research designing a thermal compensation system, x-ray microbeams, and space technologies for communications and motor control. Since 2007, he has collaborated with several Italian and English blogs and magazines as a technical writer, specializing in electronics and technology. From 2015 to 2018, he was the editor-in-chief of Firmware and Elettronica Open Source. Maurizio enjoys writing and telling stories about Power Electronics, Wide Bandgap Semiconductors, Automotive, IoT, Digital, Energy, and Quantum. Maurizio is currently editor-in-chief of Power Electronics News and EEWeb, and European Correspondent of EE Times. He is the host of PowerUP, a podcast about power electronics. He has contributed to a number of technical and scientific articles as well as a couple of Springer books on energy harvesting and data acquisition and control systems.