Josephson RF Envelope Detection for Cryogenic Baseband Pulses
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Solution Overview
Problem
Current quantum computing systems face challenges in generating spectrally broad baseband signals for superconducting quantum interference devices (SQUIDs) due to signal dispersion and distortion caused by finite skin depth and impedance mismatches, especially when using dual digital-to-analog converters (DACs) in dilution refrigerators.
Innovation Solution
A Josephson Junction (JJ) envelope detector circuit is used to convert amplitude modulated radio-frequency (RF) signals into baseband control pulses, with biasing currents based on critical currents of superconducting devices, allowing near-zero quiescent dissipation and reducing dispersion and distortion by being physically close to the computing payload within the cryostat.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If room temperature DACs are used to generate baseband signals and send via high bandwidth cabling into dilution refrigerator, then signal generation capability is achieved, but signal dispersion and distortion occur due to finite skin depth and impedance mismatches
Solution Approach 1:
The patent moves the baseband signal generation from room temperature to cryogenic temperature (another dimensional change in operating temperature), placing the DAC inside the dilution refrigerator near the quantum processing unit. This eliminates the need for long cable transmissions and resolves the signal dispersion and distortion problems caused by finite skin depth and impedance mismatches.
Solution Approach 2:
The patent introduces a cryogenic DAC as an intermediary device that generates baseband signals directly at the cryogenic stage, eliminating the need for room temperature signal generation and cable transmission. This intermediary solution resolves the harmful effects of signal degradation during transmission.
2Adaptability or versatility
If dual DAC types (RF DAC and baseband DAC) are used, then both qubit control pulses and SQUID flux pulses can be generated, but device complexity and bandwidth requirements increase
Solution Approach 1:
The patent merges the RF signal generation and baseband signal generation into a single integrated system. The RF signal is generated at room temperature, modulated with baseband information, and then downconverted at the cryogenic stage to extract the baseband signal. This eliminates the need for separate RF DAC and baseband DAC, reducing device complexity while maintaining the capability to generate both qubit control pulses and SQUID flux pulses.
Solution Approach 2:
The patent creates a universal signal generation system that can produce both qubit control pulses and SQUID flux pulses using a single baseband DAC at the cryogenic stage. This multi-functional approach eliminates the need for dedicated DACs for different signal types, reducing overall system complexity.
3Measurement precision
If envelope detector is placed inside cryostat near quantum processing unit, then signal dispersion and distortion are minimized, but heat dissipation becomes a concern
Solution Approach 1:
The patent utilizes the unique parameter of Josephson junctions - their ability to operate in a superconducting state with zero electrical resistance at cryogenic temperatures. By biasing the envelope detector based on the critical current of the Josephson junctions, the system achieves near-zero quiescent power dissipation, allowing the detector to be placed inside the cryostat near the quantum processing unit without significant heat dissipation concerns.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution minimizes signal dispersion and distortion, eliminates the need for separate DACs for RF and baseband signals, and enables efficient generation of baseband signals for quantum computing payloads, improving the overall performance of quantum computing systems.
Implementation Method 1
The JJ devices are in a supercurrent state with zero quiescent power dissipation when the envelope detector circuit is not receiving RF signals
Implementation Method 2
A Josephson Junction (JJ) envelope detector circuit is used to convert amplitude modulated radio-frequency (RF) signals into baseband control pulses
Data Source
AI summary
A method of using Josephson Junctions to convert the envelope of radio-frequency signals into baseband control pulses includes injecting a biasing current into an envelope detector circuit. The biasing current is identified based on first and second critical currents of superconducting devices in the envelope detector circuit. The first critical current corresponds to the envelope detector circuit receiving no RF signals. The second critical current corresponds to the envelope detector circuit receiving maximum RF signals. The method further includes receiving a modulated radio frequency (RF) signal at the envelope detector circuit to detect an envelope of the received RF signal. The output of the envelope detector circuit is used to drive an output load. The output is generated based on the detected envelope by the envelope detector circuit.