Feature: Interconnects
Figure 1: Cryogenic connector hermetic top plate – down
The connectors are compatible with .047” (1.19mm) size coax, either in 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, offering a large choice of thermal conductivity and attenuation. To minimise passive heat load, cable
materials with low thermal conductivity are preferred, however, with the exception of superconductors this typically goes hand in hand with poor electrical conductivity. Flexible cables having silver-plated copper conductors are typically used for connections from the top of the DR to connect the control electronics, and can be terminated with conventional SMA connectors. Conformable copper coax options are also available and are often used at the lowest-temperature stage.
Material match Superconducting niobium-titanium cables are often specified in quantum applications, yet this material can be challenging, if not impossible to solder. To overcome this, CryoCoax
Figure 2: Cryogenic connector feedthrough plate
developed solderless connections for these high-density connectors, as well as the traditional SMA, 2.92 and SMP connectors. Standard configurations are 8-way, 16-way and 24-way, with either smooth bore or full-detent options. Connector blocks can be ganged
together, to increase the number of coax lines. Two connector blocks form a mated pair, one with a full-detent male SMPM interface and the other with a smooth-bore SMPM male interface 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 with 0dB, 3dB, 6dB, 10dB and 20dB. CryoCoax worked with a leading
attenuator manufacturer in developing these attenuator blocks to complement the high-density connectors. Attenuators are used to suppress thermal noise and provide thermal isolation of the centre conductors. With assistance from the UK’s
National Physical Laboratory, CryoCoax proved the design’s reliability over low temperatures for a number of
Figure 3: Intelliconnect high-density cryogenic connector for quantum computing
www.electronicsworld.co.uk July/August 2023 39
thermal cycles. This was followed by in- house durability testing, to confirm that the RF performance and DC resistance remain stable after multiple mating cycles.
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