Symmetric RF SQUID Readout for Low-Noise Superconducting Qubits
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Solution Overview
Problem
Existing quantum computing systems face challenges in accurately measuring quantum states of superconducting qubits without destroying them, particularly due to interference and noise in analog microwave signals and complex circuitry, which hinder scalability and efficiency.
Innovation Solution
The use of symmetric radio frequency superconducting quantum interference device (SQUID) circuits coupled with inductors to form a phase-sensitive detector, allowing for quantum state measurement through phase detection using SFQ pulses, which are shorter and less disruptive, and compensation circuits to reduce asymmetry in SQUID devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If analog microwave signals are used to measure quantum states, then measurement capability is achieved, but noise and interference increase
Solution Approach 1:
The patent replaces analog microwave signal measurement with a digital measurement approach using a voltmeter to measure the voltage of the reflected SFQ pulse. This substitution of measurement methodology eliminates the noise and interference inherent in analog microwave signals while maintaining measurement capability, directly resolving the contradiction between measurement precision and harmful factors.
Solution Approach 2:
The patent introduces a reflectometer circuit as an intermediary device that converts the quantum state information into a reflected SFQ pulse voltage signal. This intermediary transformation allows the quantum state to be measured through a digital voltage measurement rather than direct analog microwave detection, thereby reducing noise and interference while preserving measurement accuracy.
2Measurement precision
If complex circuitry is used for quantum measurement, then measurement capability is improved, but device complexity increases
Solution Approach 1:
The patent extracts and eliminates unnecessary complex circuitry from the measurement system. By using a simple voltmeter to measure the reflected pulse voltage instead of complex analog microwave detection circuits, the patent achieves quantum state measurement with significantly reduced device complexity while maintaining measurement precision.
Solution Approach 2:
The patent replaces complex analog microwave measurement circuits with a simple digital voltage measurement system. The reflectometer circuit combined with a voltmeter provides a straightforward measurement approach that avoids the complexity of traditional analog microwave detection while achieving the same measurement objective.
3Productivity
If SFQ pulses are used for measurement, then measurement speed increases, but backaction on quantum states occurs
Solution Approach 1:
The patent uses a reflected SFQ pulse measurement approach where the measurement interaction is minimized to only what is necessary. By measuring the voltage of the reflected pulse rather than using strong measurement signals, the patent achieves fast measurement speed while reducing the backaction on the quantum state, thus maintaining quantum state integrity.
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 approach enables accurate and fast quantum state measurement with reduced backaction, minimizing noise and interference, thereby enhancing the scalability and efficiency of quantum computing systems.
Implementation Method 1
two radio frequency (RF) superconducting quantum interference device (SQUID) circuits symmetrically coupled to form a quantum readout circuit for reading a superconducting qubit
Implementation Method 2
form a phase sensitive detector that is operable to measure a phase of a signal
Data Source
AI summary
The technology disclosed in this patent document can be implemented to combine quantum computing and classical digital computing in a scalable computing system based on superconducting qubits using Josephson junctions that exhibit low dissipation long coherence times and can be fabricated with well-developed integrated circuit fabrication techniques. More specifically, the disclosed technology can be implemented by using two radio frequency (RF) superconducting quantum interference device (SQUID) circuits coupled in balance to preserve general symmetry and form a quantum readout circuit for reading and digitizing a superconducting qubit state with improved readout fidelity and sensitivity.