Ungrounded Superconducting Coupler for Faster, Accurate Quantum Gates
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Solution Overview
Problem
Existing tunable couplers in quantum computing often have idling frequencies above qubit frequencies, leading to reduced operation speed and accuracy of two-qubit gates due to cancellation of direct and indirect coupling terms, and are complex to design and calibrate.
Innovation Solution
A tunable resonator-resonator coupling circuit with ungrounded superconducting islands providing controlled indirect coupling between linear or nonlinear resonators, allowing different signs of coupling frequencies and enabling efficient interaction, simpler design and operation, and potentially lower idling frequencies for improved gate performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single-island transmon is used as the tunable coupler, then the indirect coupling can be achieved, but the idling frequency is always above the qubit frequencies which reduces operation speed and accuracy
Solution Approach 1:
The single superconducting island is divided into two separate ungrounded superconducting islands. This segmentation allows independent control of coupling frequencies and eliminates the constraint that forced the idling frequency above qubit frequencies, thereby improving both gate operation speed and accuracy simultaneously.
Solution Approach 2:
Instead of accepting the conventional single-island design where idling frequency is inherently above qubit frequencies, the patent inverts the approach by using two ungrounded islands that can be tuned to have idling frequencies below qubit frequencies, reversing the traditional frequency relationship to eliminate harmful coupling cancellation.
2Adaptability or versatility
If a tunable coupler is inserted between superconducting qubits to enable tunable interaction, then quantum gate operations can be implemented, but the direct and indirect coupling terms cancel each other at certain frequencies reducing performance
Solution Approach 1:
The patent implements dynamic control of coupling frequencies through independent flux biasing of two ungrounded superconducting islands. This allows the system to adaptively adjust coupling strengths and avoid frequency conditions where direct and indirect coupling terms would cancel each other, maintaining high gate operation accuracy across different operating points.
Solution Approach 2:
The two ungrounded superconducting islands serve as intermediary elements that mediate the interaction between qubits. By controlling the Josephson coupling between these intermediaries, the system can enable or disable indirect coupling paths independently, preventing cancellation effects while maintaining tunable interaction capability.
3Reliability
If existing tunable coupler designs are used, then indirect coupling can be provided, but the design and calibration become complex
Solution Approach 1:
By segmenting the coupler into two ungrounded superconducting islands, each island can be independently controlled through separate flux bias lines. This segmentation simplifies the control architecture compared to single-island designs, as each island's frequency can be independently tuned without affecting the other, reducing calibration complexity.
Solution Approach 2:
The two ungrounded superconducting islands provide multiple functions: they serve as both the coupling mediation elements and as independently controllable frequency tuning elements. This multi-functionality reduces the need for additional control components, simplifying the overall circuit design while maintaining reliable coupling control.
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 enables more efficient control of resonator interaction, reduces gate errors from decoherence, and simplifies the design and operation of quantum computing circuits while maintaining or improving performance compared to existing technologies.
Implementation Method 1
a Josephson coupling between the first superconducting island and the second superconducting island
Implementation Method 2
The tunable coupling element comprises a first superconducting island and a second superconducting island which are both ungrounded
Data Source
AI summary
The invention is generally related to the field of quantum computing and particularly to a tunable resonator-resonator coupling circuit that provides both direct and indirect couplings between linear or nonlinear resonators. The indirect coupling is provided by using a tunable coupling element that comprises two ungrounded superconducting islands. Since the superconducting islands are ungrounded, it is possible to provide different signs of coupling frequencies for the resonators and the superconducting islands, which in turn allows the interaction between the first and second resonators to be controlled more efficiently. Moreover, the design, calibration, and operation of the circuit with such a tunable coupling element are significantly easier and simpler compared to the existing analogues, while providing the same or even better performance. A quantum computing apparatus using one or more such circuits is also provided.