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Microwave Circulator: Protecting a Qubit from Amplifier Back-Action

Toggle a 3-port microwave circulator in and out of a superconducting-qubit readout chain (qubit to amplifier) and watch whether backward amplifier noise reaches the qubit or gets redirected to a matched termination port, tracked live via qubit coherence and readout fidelity.

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Superconducting-qubit readout sends a weak probe into the qubit's resonator and the reflected, state-dependent signal out to a sensitive amplifier over the same line. The amplifier also generates its own noise, which can travel backward toward the fragile qubit. A 3-port microwave circulator routes signals in one fixed rotation — port 1 to port 2 to port 3 to port 1, never backward — so wiring the qubit to port 1, the amplifier to port 2, and a matched termination to port 3 lets the probe flow normally while redirecting backward amplifier noise to the termination instead of the qubit. Toggle the circulator in and out of the chain to see the difference in live qubit coherence and readout fidelity.

⚙ Under the hood

Toggle a 3-port microwave circulator in and out of a superconducting-qubit readout chain (qubit → circulator → amplifier, with a matched termination on the third port) and watch a live probe signal flow correctly in both cases while amplifier back-action noise either reaches the qubit unchecked (circulator out) or gets redirected to the termination port and safely absorbed (circulator in), tracked through live qubit-coherence and readout-fidelity meters that demonstrate the nonreciprocal 1→2→3→1 rotational routing pattern of a true circulator versus a simple 2-port isolator.

microwave circulatornonreciprocal devicesuperconducting qubitqubit readoutamplifier back-action3-port routingcold terminationquantum coherence

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