Bandpass Josephson Parametric Amplifier for Stable Qubit Readout
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Solution Overview
Problem
Existing Josephson Traveling Wave Parametric Amplifiers (JTWPAs) have wide amplification bands that lead to instability and noise amplification during qubit readout, and are sensitive to impedance mismatches, making them difficult to integrate with other microwave devices in quantum processors.
Innovation Solution
A bandpass parametric amplifier circuit with a nonlinear distributed bandpass filter architecture, incorporating linear resonators and high characteristic impedance to achieve phase matching and reduce noise, allowing for medium-range bandwidth centered around qubit readout frequencies, and using impedance matching networks for proper integration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a wide amplification band is used in JTWPA, then the amplification range is large, but irrelevant signals and quantum noise are amplified causing instability
Solution Approach 1:
The amplification band is segmented into a specific frequency range using bandpass filtering. The JTWPA is combined with input and output bandpass filters that have complementary frequency responses, creating a defined amplification window centered at the qubit readout frequency while rejecting out-of-band signals.
Solution Approach 2:
The amplification characteristic is made local to a specific frequency band rather than being uniform across a wide range. The bandpass filters are designed with specific center frequencies and bandwidths tailored to the qubit readout frequency, providing selective amplification only where needed.
2Reliability
If wideband magnetic-based isolators are added for impedance matching, then impedance mismatch effects are minimized, but integrability with other microwave devices is limited
Solution Approach 1:
Magnetic-based wideband isolators are replaced with superconducting bandpass filters that provide impedance matching through their resonant structures. These filters are compatible with superconducting quantum circuits and can be integrated using the same fabrication processes, eliminating the need for magnetic components.
Solution Approach 2:
The impedance matching approach is changed from wideband magnetic isolators to narrowband superconducting bandpass filters. The filters are designed with specific characteristic impedances and frequency responses that provide matching at the qubit readout frequency while maintaining compatibility with superconducting devices.
3Power
If a large array of Josephson junctions is used, then parametric amplification is achieved, but the amplification band becomes too large for qubit readout
Solution Approach 1:
The frequency response of the amplifier is segmented using bandpass filters at the input and output. The input filter limits the frequencies that enter the JTWPA, and the output filter selects only the desired frequency range for amplification, creating a defined operational bandwidth despite the broadband nature of the JTWPA itself.
Solution Approach 2:
Bandpass filters are introduced as intermediary components between the signal source and the JTWPA, and between the JTWPA and the load. These filters mediate the frequency selection, allowing the JTWPA to provide high gain while the filters ensure that only the desired frequency band is amplified.
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
The solution provides a directional amplifier that amplifies weak microwave signals with minimal noise, enabling high-fidelity quantum non-demolition measurements and reducing unwanted backaction on qubits, while being compatible with other microwave devices and relaxing strict impedance matching requirements.
Implementation Method 1
a nonlinear transmission line, whose center conductor comprises a large array of Josephson junctions
Implementation Method 2
Each unit cell may include a resonant structure, including: a third capacitor having a first node coupled to a center conductor; a third inductor having a first node coupled to a second node of the third capacitor
Data Source
AI summary
A bandpass parametric amplifier circuit includes a plurality of unit cells. At least one unit cell includes a first inductor having a first node coupled to a center conductor and a second node coupled to ground. There is a first capacitor having a first node coupled to the center conductor and a second node coupled to ground. There is a second inductor having a first node coupled to the center conductor. A second capacitor has a first node coupled to a second node of the second inductor. The second capacitor and the second inductor are in series with the center conductor.