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Cryogenic wiring, explained
Every signal line into a cryostat is also a path for heat. As experiments grow from a few lines to hundreds, the wiring decides how cold the experiment stays and how much fits inside.
The four constraints
Heat load
Each conductor carries heat from warmer stages to colder ones. The cooling power available at the coldest stage is small, so the thermal conductance of every line counts.
Line count
A qubit needs control and readout lines. As the number of qubits or detector pixels grows, the number of lines grows with it.
Signal integrity
Microwave lines need controlled impedance, attenuation at the right stages and low crosstalk, so that thermal noise from warmer stages does not reach the device.
Space
Coaxial cables, connectors and attenuators take up room on every plate. A cryostat runs out of space before it runs out of cooling power more often than people expect.
What flexible cryogenic cables change
Instead of one coaxial cable per line, a flex cable carries many transmission lines side by side on a thin, flexible substrate. Using superconducting conductors in the cold sections keeps electrical loss low while conducting very little heat, and the flat format packs many lines into the space of a few coaxial cables.
Delft Circuits builds this kind of cabling as Cri/oFlex®, for qubit control and readout and other low-temperature experiments. Cri/oFlex® in detail.
Questions to answer before you specify wiring
- How many lines of each type: DC, RF drive, flux bias, readout in and out?
- What frequency range does each line need?
- What cooling power is available at each stage of your cryostat?
- Where should attenuation and filtering sit?
- Which connectors and feedthroughs does your cryostat use?
Send us the answers and we will work out the configuration with Delft Circuits.
Planning the wiring for a new or upgraded system?
Tell us the cryostat and the line count. We will come back with a Cri/oFlex® configuration and quotation.