Qubit Readout Amplifier Matching With Pump Tone Filtering

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Solution Overview

Problem

In quantum computing, reflected amplifier pump signals can interfere with qubits, degrading their performance and causing decoherence due to frequency matching issues between the pump tone and the measurement resonator, leading to attenuated measurement signals and reduced signal-to-noise ratios.

Innovation Solution

Incorporating a frequency filter in the output signal line between the measurement resonator and the amplifier, and modifying the pump tone frequency to fall outside the filter's frequency range, effectively attenuating the reflected pump signal and protecting the qubit from decoherence while allowing the amplifier to still amplify measurement signals.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a frequency filter is added to attenuate reflected pump signals, then qubit protection from decoherence is improved, but device complexity increases

Engineering Contradiction:

Improvequbit readout fidelityVSAvoidfilter integration complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The frequency filter is nested within the existing readout resonator structure, where the filter is implemented as a coupled resonator system. The readout resonator and filter share common circuit nodes and transmission lines, allowing the filter functionality to be embedded within the existing architectural framework rather than adding completely separate components.

Inventive Principle:

Principle #7Nested doll (Nesting)

Solution Approach 2:

The readout resonator serves multiple functions: it acts as both the primary readout element for qubit state detection and as part of the frequency filtering system. By designing the resonator with coupled modes, it simultaneously performs signal readout and pump tone rejection, eliminating the need for completely separate filter components.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Object-affected harmful factors

If the pump frequency is moved outside the filter frequency range, then reflected signal attenuation is improved, but amplifier bandwidth requirements increase

Engineering Contradiction:

Improvereflected pump signal interferenceVSAvoidamplifier bandwidth

Core Design Contradiction:

Object-affected harmful factorsVSAdaptability or versatility

Solution Approach 1:

The system utilizes frequency parameter optimization by selecting specific pump frequencies that are offset from the readout resonator frequency by amounts determined by the filter's frequency response characteristics. The patent identifies optimal frequency offsets that maximize pump rejection while maintaining sufficient amplifier bandwidth, transforming a potential constraint into a design parameter for optimization.

Inventive Principle:

Principle #35Parameter changes

3Device complexity

If a frequency filter is used instead of a circulator, then device cost and complexity are reduced, but filter design precision requirements increase

Engineering Contradiction:

Improvecomponent countVSAvoidfilter frequency matching

Core Design Contradiction:

Device complexityVSManufacturing precision

Solution Approach 1:

The patent employs feedback mechanisms during the frequency tuning process, where the system monitors the interaction between the readout resonator and filter modes and adjusts coupling parameters accordingly. This feedback approach allows for achieving the required frequency matching precision through iterative optimization rather than requiring extremely tight initial manufacturing tolerances.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The system utilizes dynamic frequency tuning capabilities where the operating frequencies of the readout resonator and filter can be adjusted after fabrication. By making the frequency characteristics可调 (tunable), the system can achieve precise frequency matching in operation even if initial manufacturing tolerances are not extremely tight, converting a static precision requirement into a dynamic adjustment capability.

Inventive Principle:

Principle #15Dynamics

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 enhances the signal-to-noise ratio and improves qubit readout fidelity by preventing interference from reflected pump tones, using less complex and costly frequency filters instead of circulators, and maintaining sufficient bandwidth for amplifying measurement signals.

Implementation Method 1

protecting a qubit and measurement resonator from reflected amplifier pump signals by including a frequency filter in an output signal line between the measurement resonator and the amplifier

Methodology Applied

Scientific EffectFrequency filtering: Filter (electronic)

Implementation Method 2

an amplifier device coupled to the readout device, in which the amplifier device may be configured to amplify a measurement signal from the readout device upon receiving a pump signal

Methodology Applied

Scientific EffectSignal amplification: Magnetic Amplifier

Data Source

PatentUS11777462B2Amplifier frequency matching for qubit readout

Publication Date: 2023.10.03 GOOGLE LLC

AI summary

A quantum computing devices includes: a qubit; a readout device coupled to the qubit, the readout device including a frequency filter having a filter frequency range; and an amplifier device coupled to the readout device, in which the amplifier device is configured to amplify a measurement signal from the readout device upon receiving a pump signal having a pump frequency that is outside of the filter frequency range of the frequency filter.