Superconducting Quantum Gate Control for Residual ZZ Cancellation
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Solution Overview
Problem
The residual ZZ interaction in fixed-frequency superconducting quantum processors causes decoherence and accuracy issues in 2-quantum gate operations, and existing methods using DC-SQUIDs are prone to magnetic flux noise, shortening coherence time.
Innovation Solution
A quantum gate device with a qubit substrate and a coupler qubit irradiated by drive pulses to eliminate residual ZZ interactions, using cross-Rabi transition drive pulses and frequency-shifted pulses to modulate resonance frequencies without external magnetic flux.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If DC-SQUIDs are used to change the resonance frequency of coupling elements and data qubits to remove residual ZZ interaction, then the residual ZZ interaction is eliminated, but the quantum processor becomes affected by magnetic flux noise and coherence time is shortened
Solution Approach 1:
The patent changes the control parameter from external magnetic flux to microwave pulse frequency and phase. By applying microwave pulses at specific frequencies (cross-Rabi transition frequency) and phases, the system achieves ZZ interaction cancellation without requiring DC-SQUID flux tuning, thereby eliminating magnetic flux noise while maintaining interaction control
Solution Approach 2:
The patent replaces the mechanical/physical flux-tuning mechanism (DC-SQUIDs requiring external magnetic flux control) with an electromagnetic field-based control mechanism (microwave pulse irradiation). This substitution eliminates the need for magnetic flux manipulation while achieving the same goal of ZZ interaction control through quantum state manipulation
2Measurement precision
If 2-quantum gate operation time is extended to achieve accurate gate control, then gate accuracy is improved, but decoherence increases due to longer operation time
Solution Approach 1:
The patent employs periodic microwave pulse sequences with specific timing and phase relationships to achieve ZZ interaction cancellation. By using periodic action at the cross-Rabi transition frequency, the system can eliminate residual interactions while maintaining short overall gate operation times, thus improving accuracy without extending duration
Solution Approach 2:
The patent applies preliminary anti-action by canceling the residual ZZ interaction through microwave pulse sequences before performing the main 2-quantum gate operation. This preliminary cancellation of harmful interactions creates a cleaner quantum environment, enabling more accurate gate control within shorter timeframes by preventing decoherence sources from accumulating
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
Eliminates residual ZZ interactions and enables 2-quantum gate operations with improved accuracy and coherence, eliminating the need for external magnetic flux.
Implementation Method 1
The pulse irradiator irradiates a first cross-Rabi transition drive pulse defined by the frequency ωc+|ω1−ω2| and a residual ZZ interaction elimination drive pulse of frequency ωc+|ω1−ω2|−δ
Implementation Method 2
utilizing cross-Rabi transitions and AC Stark shifts to modulate resonance frequencies
Data Source
AI summary
A quantum gate device includes a qubit substrate that includes at least two data qubits, namely a first data qubit and a second data qubit, and a coupler qubit disposed between the first data qubit and the second data qubit and a pulse irradiator that irradiates drive pulses to the coupler qubit. The pulse irradiator irradiates a first cross-Rabi transition drive pulse and a residual ZZ interaction elimination drive pulse, which is shifted by a predetermined frequency from the first cross-Rabi transition drive pulse. The predetermined frequency shift is a value that eliminates the residual ZZ interaction between the first data qubit and the second data qubit.