Intelliconnect, a company that supplies RF and Microwave interconnect products to many of the leading American and European Defense, Medical, and Marine OEMs, has developed high-density multi-way connectors to improve and simplify the architecture of quantum computers. These connectors are available in standard configurations such as 8-way, 16-way, and 24-way with either smooth bore or full detent options. They not only allow many more coaxial lines in a given space but also simplify the installation and customization within a dilution refrigerator (DR), a system used to operate quantum processors at temperatures near absolute zero.
These connections have traditionally been done with individual coaxial cables fitted with SMA connectors which offer limited packaging due to their 8 mm hex coupling nut, which also requires space for the applications of tooling during installation. In this case, High-Density connector blocks can be ganged together to potentially give hundreds of coaxial lines in a dilution refrigerator.
These interconnects are used in conjunction with ‘bullet’ style female to female SMPM adaptors fitted between a pair of connector blocks. The ‘bullet’ adaptors are retained in the full detent connector block. These can be combined with 8-way, 16-way and 24-way attenuator blocks available in 0 dB, 3 dB, 6 dB, 10 dB and 20 dB.
CryoCoax, a division of IntelliConnect which is responsible for developing quantum computing related products, has worked with a leading attenuator manufacturer in developing these attenuator blocks to compliment the high-density connectors. Attenuators are employed to suppress thermal noise and provide thermalization of the centre conductors.
Each cooling stage is separated by a bulkhead/heatshield to minimize heat transfer. The cables are installed between each of these stages and connect via feedthrough connectors and must provide good thermalization. Thorough thermalization of cables, attenuators, and microwave components at the various temperature stages is not only important for reducing the heat load on the dilution refrigerator, but also for reducing thermal noise within the system.
These connectors offer compatibility with .047” (1.19 mm) size coax, either semi-rigid, flexible or conformable versions. Semi-rigid cables are available in niobium-titanium, stainless steel, copper, cupronickel and beryllium copper as well as combinations of these with silver-plated conductors, providing the user with a large choice in terms of thermal conductivity and attenuation.
To minimize passive heat load, cable materials with low thermal conductivity are normally favored; however, with the exception of superconductors, this typically goes hand in hand with poor electrical conductivity.
Flexible cables with silver-plated copper conductors are typically used for connections from the top of the DR to connect the control electronics at room temperature and can be terminated with conventional SMA connectors. Conformable copper coax options are also available and are often used at the lowest stage.
Superconducting niobium-titanium cables are often specified in quantum applications. This material can be challenging, if not impossible to solder. To overcome this, CryoCoax developed solderless connections for these high-density connectors as well as the traditional SMA, 2.92 mm & SMP connectors.
With assistance from NPL (National Physical Laboratory), the company was able to prove the low-temperature reliability of the design over a number of thermal cycles, this was followed by in-house durability testing to confirm that the RF performance and DC resistance remained stable after multiple mating cycles.
Click here to learn more about CryoCoax interconnect solutions.
Click here to learn more about these high-density connectors from Intelliconnect and CryoCoax.
