Qubit Readout Amplifier Matching With Off-Band Pump 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 reduced signal-to-noise ratios and measurement fidelity.
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 be outside the filter's frequency range, effectively attenuating the reflected pump signals and preventing them from reaching the qubit, while ensuring the amplifier can still amplify measurement signals within its bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the pump tone frequency is matched to the measurement resonator frequency for efficient amplification, then the amplifier gain is improved, but the reflected pump signals interfere with the qubit causing decoherence
Solution Approach 1:
A frequency filter is introduced as an intermediary component between the amplifier and the qubit. This filter selectively passes the measurement resonator frequency while blocking the pump tone frequency, thereby mediating between the need for amplification and the need to protect the qubit from decoherence
Solution Approach 2:
The pump tone frequency is deliberately changed to be different from the measurement resonator frequency. This parameter change allows the amplifier to operate at optimal gain for the resonator frequency while the reflected pump signals at the different frequency are filtered out before reaching the qubit
2Object-affected harmful factors
If a frequency filter is added to block reflected pump signals, then the qubit protection is improved, but the device complexity increases
Solution Approach 1:
The patent employs a relatively simple and inexpensive frequency filter rather than complex active components like circulators. This disposable-like approach prioritizes functionality and cost-effectiveness over minimal circuit complexity
3Object-affected harmful factors
If the pump frequency is shifted outside the filter frequency range to reduce reflections, then the qubit protection is improved, but the amplifier bandwidth requirements increase
Solution Approach 1:
The pump frequency is changed to a value outside the measurement resonator frequency, creating a frequency separation that allows the filter to block reflected pump signals while passing the resonator signal. This parameter change accommodates the amplifier's bandwidth characteristics
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 enhances measurement fidelity by filtering out interfering frequencies, using less complex and costly components compared to circulators.
Implementation Method 1
including a frequency filter in an output signal line between the measurement resonator and the amplifier, and by modifying the pump tone frequency so the frequency of the reflected signal falls outside of a filter frequency range of the filter
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 of the frequency filter
Data Source
Figure 1
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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.