As quantum computing transitions from theoretical physics and academic laboratories into scalable, commercial enterprise infrastructure, the engineering challenges have evolved from basic qubit creation to the complex infrastructure required to support them. Chief among these bottlenecks is the physical and electrical interface between the room-temperature classical computing world and the ultra-cold, sub-kelvin environment where quantum processors operate.
In a recent special episode of Electronic Design’s Inside Electronics podcast—sponsored by industry heavyweights DigiKey and Amphenol—David Maliniak, senior editor at Microwaves & RF, sat down with industry experts James Merryman of Amphenol SV Microwave and Benjamin Pratt of Amphenol CDI. The discussion illuminated the specialized engineering, material science, and collaborative design approaches required to build reliable cryogenic interconnects for next-generation quantum-computing systems.
Main Facts
The fundamental physics governing quantum computing impose extreme constraints on hardware design. Superconducting quantum computers rely on qubits (quantum bits) that must operate at millikelvin temperatures—close to absolute zero—to maintain quantum coherence. At these temperatures, even minute environmental disturbances can introduce decoherence, leading to computational errors.
Key takeaways from the discussion highlight the critical nature of these systems:
- The Material Challenge: Ferromagnetic materials, commonly used in standard electronic connectors, are strictly forbidden near the qubits. Even trace amounts of magnetism can disrupt the delicate magnetic fields required to control and read out qubits, causing severe system instability and skyrocketing error rates.
- Thermal and Mechanical Stress: Cryogenic systems undergo violent thermal cycling, dropping from room temperature (approx. 295K) down to cryogenic plateaus, including 4K, 1K, and ultimately millikelvin ranges (10–100 mK). Materials must contract and expand predictably without failing, cracking, or introducing mechanical stress on printed circuit boards (PCBs).
- High-Density Signal Routing: As quantum processors scale from dozens of physical qubits to thousands, the physical real estate inside dilution refrigerators becomes critically scarce. High-density coaxial interfaces are required to route dozens, and eventually thousands, of radio frequency (RF) control and readout lines without thermal bridging.
- Comprehensive Ecosystem Offerings: Amphenol CDI and SV Microwave provide an end-to-end suite of specialized hardware—including non-magnetic connectors, hermetic feedthroughs, attenuation networks, and solderless, high-density coaxial PCB interfaces like CDI’s CoreCryo system—supported by DigiKey’s global distribution and supply-chain infrastructure.
Chronology of an Evolution: From Benchtop Physics to Scalable Hardware
To understand how cryogenic interconnects became a focal point of modern electronics engineering, it is necessary to examine the chronological evolution of quantum computing hardware.
Phase I: The Academic and Proof-of-Concept Era (Early 2000s–2010s)
In the early days of superconducting circuit research, systems were small, typically hosting anywhere from one to a handful of qubits. Interconnects were largely improvised. Researchers utilized standard, off-the-shelf SMA or coaxial connectors and semi-rigid cables plucked from traditional RF laboratories.
At this scale, thermal management was straightforward, and signal density was low enough that bulky connectors could fit easily inside standard dilution refrigerators. Material purity was rarely tracked with the meticulous precision demanded today, as the primary goal was demonstrating fundamental quantum phenomena rather than building a reliable commercial computer.
Phase II: The Scaling Bottleneck (Mid-2010s–2020)
As the industry shifted toward "Noisy Intermediate-Scale Quantum" (NISQ) processors, qubit counts scaled into the 50-to-100 range. Suddenly, the dilution refrigerator became a traffic jam of coaxial cables. Engineers quickly realized that standard commercial RF connectors introduced massive thermal loads (heat leaks from room temperature down to the mixing chamber) and spatial bottlenecks.
Furthermore, unexplained qubit decoherence began plaguing systems. Material analysis revealed that standard plating materials, such as nickel underlays beneath gold plating, exhibited ferromagnetic properties at cryogenic temperatures. The industry faced a sudden, urgent need for custom, non-magnetic, high-density RF hardware.
Phase III: The Industrialization and Co-Design Era (2020–Present)
Today, quantum computing has entered an industrialization phase. Companies are targeting thousands of physical qubits, requiring error-corrected architectures. This transition necessitated a complete reimagining of the signal chain.
During the Inside Electronics podcast, leaders from Amphenol CDI and SV Microwave detailed how modern engineering teams now practice "co-design"—integrating connector topology, board layout, and refrigeration architecture from the very inception of a quantum system. Rather than treating connectors as an afterthought, hardware architects now rely on specialized, highly engineered ecosystems like CDI’s CoreCryo and SV Microwave’s multi-port density systems (MDRF) to bridge the macro and micro worlds reliably.
Supporting Data and Technical Architecture
Designing electronics for the millikelvin regime requires bending traditional electrical engineering rules. At room temperature, impedance matching, signal integrity, and insertion loss are well-understood. At 20 millikelvins, those challenges are compounded by thermodynamics, quantum mechanics, and solid-state physics.
The Anatomy of a Dilution Refrigerator Thermal Stack
A typical dilution refrigerator used in quantum computing features multiple temperature stages, each acting as a thermal shield:
- Room Temperature (approx. 300K): The external control electronics, arbitrary waveform generators (AWGs), and vector network analyzers (VNAs).
- The 50K Plate: The first major cooling stage, where high-frequency coaxial lines begin dropping thermal energy.
- The 4K Plate: Liquid helium temperature stage, where traditional superconducting materials begin to show zero electrical resistance. Attenuation is frequently applied here to suppress thermal noise from room temperature.
- The Still (approx. 800mK): A transitional stage for pumping out helium-3 gas.
- The Mixing Chamber (10mK–100mK): The heart of the quantum processor. This is where the quantum chip resides.
According to James Merryman of Amphenol SV Microwave, non-magnetic connectors are most critical at this final stage. "When you get right down to the mixing chamber, adjacent to the qubits, even trace ferromagnetic materials can disrupt the local magnetic environment," Merryman explained during the podcast. "That disruption leads directly to a loss of qubit coherence and spikes your system’s overall error rates."
Higher up in the refrigerator—at the 4K or 50K stages—the sensitivity drops off slightly, allowing the use of conventional RF materials where structural rigidity or cost optimization takes priority.
Overcoming Mechanical Stress and Signal Density
Benjamin Pratt of Amphenol CDI elaborated on the engineering innovations required to handle the physical realities of thermal cycling. When a refrigerator cools from 300K to 10mK, different metals contract at different rates. If a connector or PCB interface is improperly designed, this differential thermal contraction creates immense shear stress, leading to cracked solder joints, micro-fractures, and catastrophic signal loss.
To combat this, Amphenol CDI developed CoreCryo, a solderless, high-density coaxial PCB interface. Key technical features include:
- Non-Ferrous Material Selection: Utilization of specialized beryllium-copper alloys, high-purity copper, and custom gold-plating techniques that completely eliminate nickel underlays.
- Solderless Compression Architecture: By avoiding traditional solder, the CoreCryo interface accommodates physical movement during thermal contraction without fatiguing the joints.
- Hermetic Feedthrough Integration: Ensures vacuum integrity across the various temperature plates of the dilution refrigerator while maintaining clean 50-ohm impedance matching.
- Integrated Attenuation and Filtering: Custom components built directly into the interconnect stack to strip out high-frequency thermal noise before it reaches the quantum processor.
Complementing CDI’s board-level interfaces, SV Microwave provides an extensive portfolio of discrete PCB connectors, cable assemblies, panel-mount components, and feedthroughs, alongside their high-density Multiport DC/RF (MDRF) interconnect systems. These modular platforms allow quantum architects to scale from 8-channel test setups to dense, multi-hundred-channel production architectures seamlessly.
Official Responses and Industry Perspectives
The conversation between David Maliniak, James Merryman, and Benjamin Pratt underscored a vital shift in how component manufacturers view the quantum market. No longer viewed as a speculative academic sideline, quantum computing is driving rigorous, mission-critical engineering standards.
The Imperative of Material Purity
"You cannot simply take an off-the-shelf catalog connector designed for a base station or an aerospace application and drop it into a dilution refrigerator," James Merryman emphasized during the podcast. "The physics of the environment are unforgiving. Manufacturers must trace their raw materials back to the mill, ensuring zero contamination of nickel or other ferromagnetic impurities. The tolerance for error is effectively zero."
Simplifying the Scaling Journey
Benjamin Pratt highlighted how modularity and rigorous testing are easing the deployment burden for quantum developers. "Our customers—ranging from national laboratories and academic institutions to major tech conglomerates—are trying to solve immense algorithmic and software challenges," Pratt noted.
"They shouldn’t have to reinvent the wheel when it comes to basic signal routing and mechanical mounting. By offering standard eight- and 16-channel configurations, fully tested products, and pre-engineered models, we give them a reliable foundation. At the same time, because every quantum system architecture is slightly unique, we maintain the engineering agility to provide fully customized solutions."
Furthermore, the involvement of global distributors like DigiKey ensures that these specialized, highly sensitive components are accessible to engineering teams worldwide. Through digital supply-chain platforms, developers can source engineering models, prototyping kits, and production-ready hardware efficiently, accelerating the global development timeline of fault-tolerant quantum computers.
Implications for the Future of Quantum Engineering
The advancements in cryogenic interconnect technology discussed by Amphenol CDI, SV Microwave, and DigiKey carry profound implications for the broader technology landscape.
1. Accelerating the Path to Fault Tolerance
Error correction is the single greatest hurdle facing quantum computing today. Because physical qubits are inherently noisy, logical qubits must be constructed by grouping dozens or hundreds of physical qubits together. This multiplies the required control and readout lines exponentially. Without high-density, non-magnetic, thermally optimized interconnects like CoreCryo and MDRF systems, scaling to the thousands of physical qubits needed for fault-tolerant quantum utility would be physically impossible.
2. Cross-Industry Technology Spillover
The rigorous materials science and thermal-management techniques developed for quantum computing are already finding applications in adjacent high-tech sectors. Ultra-low-temperature electronics are increasingly vital in space exploration (such as deep-space radio astronomy receivers), cryo-electronics for high-performance computing (HPC) supercomputers, and advanced medical imaging systems. The engineering playbook written for millikelvin interconnects will undoubtedly fortify other extreme-environment engineering disciplines.
3. Deepening Ecosystem Collaboration
The collaboration between distributors like DigiKey and component manufacturers like Amphenol highlights a maturing commercial ecosystem. As quantum computing transitions from physics experiments to standardized hardware procurement, the availability of catalog-ready, tested, and customizable cryogenic hardware lowers the barrier to entry for new market entrants, fostering a more competitive and innovative industry.
Conclusion
As the quantum computing industry marches toward practical utility, the hidden infrastructure within the dilution refrigerator will ultimately determine what is computationally possible. Through meticulous material science, innovative mechanical design, and robust supply-chain partnerships, engineering pioneers are solving the thermal and electromagnetic puzzles of the sub-kelvin world—ensuring that the bridge between classical and quantum computing remains strong, stable, and ready to scale.
