A radio-frequency (RF) to direct current (DC) converter is provided. When a DC electrical current is applied via a DC input port of the converter, the DC electrical current is shunted to ground through a Josephson junction (JJ) of the converter and substantially no DC electrical current flows through a resistor of the converter, and when an RF electrical current is applied via an RF input port of the converter, output trains of SFQ current pulses from a DC to SFQ converter of the RF-to-DC converter with pulse-to-pulse spacing inversely proportional to the RF electrical current frequency cause the JJ to switch at a rate commensurate with an RF frequency of the RF electrical current to generate a steady state voltage across the JJ linearly dependent on the RF frequency.

High-saturation power Josephson ring modulators and fabrication of the same are provided. A Josephson ring modulator can comprise a plurality of matrix junctions. Matrix junctions of the plurality of matrix junctions can comprise respective superconducting parallel branches that can comprise a plurality of Josephson junctions operatively coupled in a series configuration. A method can comprise forming a first matrix junction comprising arranging a first group of Josephson junctions as first parallel branches. The method can also comprise forming a second matrix junction comprising arranging a second group of Josephson junctions as second parallel branches. Further, the method can comprise forming a third matrix junction comprising arranging a third group of Josephson junctions as third parallel branches. In addition, the method can comprise forming a fourth matrix junction comprising arranging a fourth group of Josephson junctions as fourth parallel branches.

High-saturation power Josephson ring modulators and fabrication of the same are provided. A Josephson ring modulator can comprise a plurality of matrix junctions. Matrix junctions of the plurality of matrix junctions can comprise respective superconducting parallel branches that can comprise a plurality of Josephson junctions operatively coupled in a series configuration. A method can comprise forming a first matrix junction comprising arranging a first group of Josephson junctions as first parallel branches. The method can also comprise forming a second matrix junction comprising arranging a second group of Josephson junctions as second parallel branches. Further, the method can comprise forming a third matrix junction comprising arranging a third group of Josephson junctions as third parallel branches. In addition, the method can comprise forming a fourth matrix junction comprising arranging a fourth group of Josephson junctions as fourth parallel branches.

A circuit is presented which includes a first amplifier having an input, a transmission line having first and second ends. The first end of the transmission line is coupled to an input of the first amplifier and a plurality of channels. Each channel includes a plurality of resonators arranged to read out a plurality of qubits, respectively and a readout line arranged to receive read out signals from the plurality of resonators. The readout line of each channel is coupled to the transmission line and each channel is configured to output a respective signal in a respective frequency band which is different from frequency bands of other channels in the plurality of channels.

A circuit is presented which includes a first amplifier having an input, a transmission line having first and second ends. The first end of the transmission line is coupled to an input of the first amplifier and a plurality of channels. Each channel includes a plurality of resonators arranged to read out a plurality of qubits, respectively and a readout line arranged to receive read out signals from the plurality of resonators. The readout line of each channel is coupled to the transmission line and each channel is configured to output a respective signal in a respective frequency band which is different from frequency bands of other channels in the plurality of channels.

Superconducting output amplifiers with interstage filters and related methods are described. An example superconducting output amplifier includes a first superconducting output amplifier stage and a second superconducting output amplifier stage. The superconducting output amplifier may further include a first terminal for receiving a first single flux quantum (SFQ) pulse train and coupling the SFQ pulse train to each of the first superconducting output amplifier stage and the second superconducting output amplifier stage. The superconducting output amplifier may further include an interstage filter comprising a damped Josephson junction (JJ) coupled between the first superconducting output amplifier stage and the second superconducting output amplifier stage, where the interstage filter is arranged to reduce distortion in an output voltage waveform generated by the superconducting output amplifier in response to at least the first SFQ pulse train.

Superconducting output amplifiers with interstage filters and related methods are described. An example superconducting output amplifier includes a first superconducting output amplifier stage and a second superconducting output amplifier stage. The superconducting output amplifier may further include a first terminal for receiving a first single flux quantum (SFQ) pulse train and coupling the SFQ pulse train to each of the first superconducting output amplifier stage and the second superconducting output amplifier stage. The superconducting output amplifier may further include an interstage filter comprising a damped Josephson junction (JJ) coupled between the first superconducting output amplifier stage and the second superconducting output amplifier stage, where the interstage filter is arranged to reduce distortion in an output voltage waveform generated by the superconducting output amplifier in response to at least the first SFQ pulse train.

A radio-frequency (RF) to direct current (DC) converter is provided. When a DC electrical current is applied via a DC input port of the converter, the DC electrical current is shunted to ground through a Josephson junction (JJ) of the converter and substantially no DC electrical current flows through a resistor of the converter, and when an RF electrical current is applied via an RF input port of the converter, output trains of SFQ current pulses from a DC to SFQ converter of the RF-to-DC converter with pulse-to-pulse spacing inversely proportional to the RF electrical current frequency cause the JJ to switch at a rate commensurate with an RF frequency of the RF electrical current to generate a steady state voltage across the JJ linearly dependent on the RF frequency.

A radio-frequency (RF) to direct current (DC) converter is provided. When a DC electrical current is applied via a DC input port of the converter, the DC electrical current is shunted to ground through a Josephson junction (JJ) of the converter and substantially no DC electrical current flows through a resistor of the converter, and when an RF electrical current is applied via an RF input port of the converter, output trains of SFQ current pulses from a DC to SFQ converter of the RF-to-DC converter with pulse-to-pulse spacing inversely proportional to the RF electrical current frequency cause the JJ to switch at a rate commensurate with an RF frequency of the RF electrical current to generate a steady state voltage across the JJ linearly dependent on the RF frequency.

A cryogenic parametric amplifier control apparatus is disclosed. Methods of implementation and devices incorporated within the whole of the apparatus are disclosed. Methods of reducing the number of signal lines necessary to control a parametric amplifier are disclosed. Schema allowing for control of multiple parametric amplifiers with a single apparatus are disclosed.