Qubit Readout Amplifier Pump Frequency Isolation

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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 preventing it from reaching the qubit, while ensuring the amplifier can still amplify measurement signals within its bandwidth.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the pump tone frequency is matched to the measurement resonator frequency for effective amplification, then the amplifier can effectively amplify measurement signals, but the reflected pump signal interferes with the qubit causing decoherence

Engineering Contradiction:

Improvequbit coherenceVSAvoidsignal amplification efficiency

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The system segments the frequency spectrum by using a bandpass filter to separate the pump tone frequency from the measurement signal frequency. The filter allows the measurement signal band to pass through to the amplifier while blocking the reflected pump tone from reaching the qubit, thus resolving the interference problem while maintaining amplification efficiency for the measurement band.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A bandpass filter is introduced as an intermediary component between the qubit and the amplifier. This filter mediates the interaction by selectively transmitting measurement signals while blocking reflected pump tones, enabling the amplifier to operate at pump tone frequencies without compromising qubit coherence.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If a frequency filter is added to block reflected pump signals, then qubit coherence is protected, but the system complexity increases

Engineering Contradiction:

Improvequbit coherenceVSAvoidsystem component count

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent employs a relatively simple and inexpensive bandpass filter rather than complex active isolation components. This filter is a passive, straightforward component that provides the necessary frequency separation without adding significant system complexity, making it a practical solution for protecting qubit coherence.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Object-affected harmful factors

If the pump tone frequency is shifted outside the filter frequency range, then reflected signal interference is reduced, but the amplifier bandwidth requirements increase

Engineering Contradiction:

Improvereflected signal interferenceVSAvoidamplifier bandwidth

Core Design Contradiction:

Object-affected harmful factorsVSAdaptability or versatility

Solution Approach 1:

The system changes the frequency parameter of the pump tone to be outside the measurement signal band but within the amplifier's operational bandwidth. This parameter adjustment allows the reflected pump signal to be blocked by the bandpass filter while the amplifier continues to effectively amplify measurement signals within its bandwidth capabilities.

Inventive Principle:

Principle #35Parameter changes

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 protects the qubit from decoherence caused by reflected pump tones, improves signal-to-noise ratios, and simplifies the system by reducing complexity and cost compared to using circulators, while maintaining the ability to amplify measurement signals effectively.

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

the amplifier device may be 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

Methodology Applied

Scientific EffectSignal amplification: Magnetic Amplifier

Data Source

PatentUS10903809B2Amplifier frequency matching for qubit readout

Publication Date: 2021.01.26 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.