Cryogenic Cables with Increased Flexibility Promote Efficient Quantum Computer Design.
Delft Circuits has announced its involvement in the BICEP project, which is being conducted in Antarctica in collaboration with NASA’s Jet Propulsion Laboratory (JPL) at the California Institute of Technology and other project partners. As part of the project, Delft Circuits will provide advanced cables that will be installed in the telescope’s cryostat, a device used to achieve low temperatures, as part of the new camera being developed. The JPL team will also replace the telescope’s sensors with thermal kinetic inductance detectors (TKIDs), which are superconductive detectors that utilize the principles of quantum mechanics.
Quantum computer design challenges
Quantum computing has gained significant interest from multinational corporations, researchers, and startups in recent years because it has the potential to overcome the limitations of current high-performance computing (HPC) systems. While HPC systems, also known as supercomputers, have high computational capacity, they are not able to solve problems that are too complex. Quantum computing, on the other hand, has the potential to offer higher computing power as the number of qubits in the system increases.
However, building a quantum computer presents unprecedented design challenges due to the need to maintain individual qubits as stable as possible and protect them from external interference. Depending on the technology used to implement the qubits, this often requires creating temperatures close to absolute zero in order to reduce noise. As a result, quantum computing hardware is usually placed inside a cryogenic dilution refrigerator.
The challenge then becomes connecting the low-temperature quantum device to the control electronics that operate at room temperature. This requires highly complex wiring, as next-generation quantum processors may contain more than a thousand qubits. Figure 1 shows the detail of a quantum computer and highlights some of the complex wiring involved in quantum computer design. While a normal coaxial cable may be sufficient to address and read a few dozen qubits, higher density interconnections are needed to support more qubits and reduce heat conduction in the dilution refrigerator.
Figure 1: Detail of a quantum computer with some connections highlighted (Source: Delft Circuits)
Delft Circuits’ solutions
Delft Circuits is a company based in Delft, Netherlands that was founded in 2017. It has developed a technology called Cri/oFlex, which is a flexible microwave cable designed specifically for use in quantum computers. This cable has a reduced form factor and is scalable as the number of qubits in the quantum computer increases. It also has a low thermal conductivity, making it easy to install and highly durable. Cri/oFlex combines cryogenic cables with standard RF connectors to create a solution that can be used with both single and multi-channel cables. The cable is made using a combination of polyimide and silver, resulting in thin, high-performing, and flexible stripline channels. Delft Circuits is focused on producing hardware for the quantum industry, particularly in the areas of input/output systems and sensors, computers, and biomedical sensing.
Figure 2: A Cri/oFlex 3 cable with SMA RF connectors (Source: Delft Circuitsu)
“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.”
The Cri/oFlex product family
Delft Circuits offers a product line called Cri/oFlex, which consists of ultra-flexible microwave input/output (I/O) cables designed for use in cryogenic environments. These cables integrate all necessary filtering components, such as low-pass filters, band-pass filters, and attenuators, to improve the robustness and reliability of the setup and reduce installation time. The Cri/oFlex product line consists of three different families, each with its own unique specifications and performance capabilities. The Cri/oFlex 1 series is suitable for vibration-sensitive instruments, such as scanning probe microscopes, and features ultra-thin and flexible microwave transmission lines. The Cri/oFlex 2 series is designed for use in densely packed sample spaces and features small, flexible RF cabling based on monolithic waveguides with high phase stability. The Cri/oFlex 3 series is the company’s flagship product, designed for scalability and featuring distributed attenuation and integrated microwave signal conditioning. It can support a high number of signal lines in a dilution refrigerator, with up to eight parallel channels and a 1-mm inter-channel pitch. These products are suitable for a variety of applications, including quantum computing, astrophysics, optics, and instrumentation.
Cri/oFlex use cases
Many of Delft Circuit’s customers, including NASA’s JPL, use microwaves at low temperatures for research purposes. JPL’s research team specifically uses Delft Circuit’s cable solutions to read out signals from microwave kinetic inductance detectors (MKIDs) which are used to measure microwave background radiation from space. These MKID devices are coupled with microwave frequency resonators to provide a high level of multiplexing, allowing for the reading of up to 1,000 detector pixels using a single MKID cable and microwave transmission measurement. These detector arrays are being expanded to tens of thousands of pixels for high-resolution imaging and require specially made cryostats with limited space and cooling capacity for installation at the bottom of telescopes. Delft Circuit is looking to expand into other fields of application for their products, such as astrophysics, STM and AFM, and biomedical imaging, in addition to their current focus on quantum computing which accounts for one-third of their total revenues.
