Sensitive, low-noise superconducting infrared photodetector

A superconductor infrared photodetector, comprising:

• a plurality of superconducting detector elements connected together, each detector element having a thin granular film of superconducting material which promotes the formation of oppositely-polarized fluxons;
• means for supplying a bias current to the detector elements, the bias current driving the fluxons to opposite sides of the film;
• and
• a SQUID readout circuit for measuring a voltage change that is induced across the detector elements by a change in the flow of fluxons when infrared radiation is incident on the detector elements;
• wherein the SQUID readout circuit is an analog SQUID readout circuit.

A superconducting photodetector, comprising:

• one or more superconducting detector elements;
• means for supplying a bias current to the detector elements;
• and
• a SQUID readout circuit for measuring changes in the flow of current due to electromagnetic radiation incident on the detector elements;
• wherein the SQUID readout circuit is digital SQUID readout circuit that operates in the tracking mode.

A superconducting photodetector, comprising:

• one or more superconducting detector elements;
• means for supplying a bias current to the detector elements;
• and
• a SQUID readout circuit for measuring changes in the flow of current due to electromagnetic radiation incident on the detector elements;
• wherein the SQUID readout circuit is an analog SQUID readout circuit.

A method for detecting electromagnetic radiation, comprising the steps of:

• biasing a thin film of superconducting material with a current;
• irradiating the thin film with electromagnetic radiation to change the flow of current;
• and
• measuring the magnitude of the change in the flow of current with a SQUID readout circuit to provide a measure of the amount of electromagnetic radiation incident on the thin film;
• wherein the step of measuring includes the steps of generating pulses only when the change in the flow of current varies by a flux quantum and counting the pulses.