Microwave oscillators based on dc SQUIDs*

We have fabricated lumped-element microwave oscillators consisting of a dc SQUID with submicron Al-AlO$_{x}$-Al junctions shunted with a capacitor formed from superconducting layers. These circuits resonate in the range of several GHz. Adjusting the current through on-chip bias lines changes the Josephson inductance of the SQUID junctions, thus varying the resonance frequency. We discuss the prospects for time-domain monitoring of the ring-down oscillations following a bias current pulse in these circuits. The discrimination of ring-down signals for different flux bias forms the basis for employing these devices in a possible new readout scheme for superconducting flux qubits.