Cryostat platform: ProteoxLX 530 mm Plate Family
A high-density 10-qubit transmon wiring system on a ProteoxLX-class dilution refrigerator. This preset is designed for thermal stress testing — it demonstrates how 210 cable routes and 10 HEMT amplifiers create meaningful thermal loads across all temperature stages. The architecture follows the standard cryogenic wiring conventions from Krinner et al. (2019), with staged attenuation on XY and readout-in lines, HEMT amplification at 4K for readout-out, and flux bias lines with reduced attenuation. Each of the 10 qubit channels has a full complement of signal chains: XY drive, flux bias, readout input, and readout output.
A dilution refrigerator cools in discrete stages. Each plate intercepts heat from the cables above and adds attenuation or filtering so thermal noise decreases as you approach the qubit at ~15 mK.
40 SMA feedthrough panels provide room-temperature access for all 10 qubit channels across 4 signal types (XY, flux, readout-in, readout-out).
First cold attenuation stage. 30 attenuators (20 dB each for XY and readout-in, 20 dB for flux) absorb the majority of room-temperature thermal noise power. Passive cable conduction from 300K is the dominant heat source.
Critical thermal stage. 30 attenuators provide second-stage attenuation. 10 HEMT amplifiers (LNF LNC4_8C class, 10.5 mW each) amplify the readout-out signal, contributing 105 mW active dissipation against a 700 mW cooling budget.
20 attenuators continue the attenuation cascade for XY and readout-in lines. By this stage, attenuator dissipation is sub-nW. Passive cable conduction is the primary load.
20 attenuators for final XY/readout-in attenuation. 10 circulators in the readout-out chain provide reverse isolation toward the qubit chip. Cooling budget is tight at 1 mW.
Base temperature stage (10–20 mK). 20 final attenuators, 10 circulators, and 10 qubit chips. The mixing chamber has only 30 uW of cooling power — every microwatt matters.
Carries 4–8 GHz microwave pulses for single-qubit gate operations. Requires 60 dB total attenuation to suppress room-temperature thermal photons at the qubit.
DC/low-frequency line for tuning qubit frequency via magnetic flux. Lower total attenuation (20–40 dB) since thermal photon suppression is less critical below ~1 GHz.
Readout probe stimulus. Same attenuation requirements as XY drive to suppress noise at the readout resonator frequency.
Returns the readout signal from the qubit chip. Uses circulators for reverse isolation and a HEMT amplifier at 4K for low-noise amplification. NbTi superconducting coax preferred below 4K to minimize insertion loss.
Staged attenuation ensures the effective noise temperature at the qubit is dominated by the coldest attenuator stage, not room-temperature Johnson noise. With 60 dB total, the thermal photon number at 6 GHz is suppressed to ~10⁻³ at 20 mK.
HEMT amplifiers at 4K are the dominant active heat source. Each LNF LNC4_8C dissipates 10.5 mW at nominal bias (0.7V × 15 mA). With 10 channels, this is 105 mW on a 700 mW budget — a significant 15% utilization.
Passive cable conduction scales linearly with the number of cables. Moving from 10 to 100 qubit channels would multiply passive loads by 10×, potentially pushing the 4K stage beyond 50% utilization.
Attenuator thermal dissipation follows a cascade: each 20 dB stage reduces the RF power by 100×, so the first attenuator (50K) absorbs ~99% of the input while the last (MXC) absorbs negligible power.
The Still and CP stages have limited cooling power (7 mW and 1 mW respectively). In large systems with hundreds of cables, passive conduction through these stages becomes a critical bottleneck.