We fabricated and tested a squelch circuit consisting of a copper powder filter with an embedded Josephson junction connected to ground. For small signals (squelch ON), the small junction inductance attenuates strongly from dc to at least 1 GHz, while for higher frequencies dissipation in the copper powder increases the attenuation exponentially with frequency. For large signals (squelch OFF), the circuit behaves as a regular metal powder filter. The measured ON/OFF ratio is larger than 50 dB up to 50 MHz. This squelch can be applied in low temperature measurement and control circuitry for quantum nanostructures, such as superconducting qubits and quantum dots.
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