passiveTier A
Circulator
Protect the qubit and resonator from amplifier back-action noise on the readout return line.
What it does
3-port passive non-reciprocal device that routes signals in one direction only (port 1→2→3→1). In real cryogenic readout chains it is commonly packaged as a slim OFHC-copper triple-junction module with SMA connectors and mounted near the MXC readout cluster.
Where it goes
- Allowed stages
- 4K, CP, MXC
- Preferred stages
- MXC
- Forbidden stages
- 300K, 50K
- Typical line types
- readoutOut
- Must sit between qubit output and HEMT amplifier.
- Often mounted in series with a second non-reciprocal device for extra isolation.
Typical specifications
| Center frequency | 4 – 8 GHz |
| Isolation | ~ 60 dB |
| Insertion loss | ~ 0.4 dB |
| RF connectors | Female SMA |
Ports
- Port 1 (from sample)inreadout50 Ω
- Port 2 (to HEMT)outreadout50 Ω
- Port 3 (50Ω load)internalreadout
Physical envelope
82.0 × 24.6 × 22.4 mm
Slim coaxial cryogenic circulator envelope aligned to the 4–8 GHz triple-junction OFHC-copper module class, with a body around 67.06 × 24.64 × 10.16 mm excluding the connectors.