Tunable Resonator Coupling Circuit With Ungrounded Islands
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Solution Overview
Problem
Existing tunable couplers in quantum computing circuits have idling frequencies above qubit frequencies, affecting operation speed and accuracy, and are prone to decoherence and resonance issues.
Innovation Solution
A tunable resonator-resonator coupling circuit with ungrounded superconducting islands providing both direct and indirect couplings, allowing controlled interaction between resonators with different coupling frequencies, and using transmon qubits to reduce noise sensitivity.
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 implemented, but the idling frequency is always above the qubit frequencies which adversely affects operation speed and accuracy
Solution Approach 1:
The patent divides the single superconducting island into multiple ungrounded superconducting islands (first superconducting island and second superconducting island). Each island is coupled to different resonators, allowing independent control of coupling frequencies. This segmentation enables the idling frequency to be positioned below qubit frequencies, resolving the contradiction between operation accuracy and speed.
Solution Approach 2:
The patent introduces flux bias lines coupled to each superconducting island, enabling dynamic control of the coupling frequencies. By adjusting the flux bias, the coupling frequencies can be tuned independently, allowing the idling frequency to be positioned below qubit frequencies while maintaining fast gate operations. This dynamic control resolves the fixed frequency limitation of single-island designs.
2Device complexity
If grounded superconducting islands are used in the tunable coupler, then the circuit design is simpler, but the control over resonator interactions is limited and decoherence issues arise
Solution Approach 1:
The patent uses ungrounded superconducting islands with flux bias lines, making the coupling frequencies dynamically controllable. This allows precise control over resonator interactions by adjusting the flux bias, achieving high control precision while maintaining relatively simple circuit architecture. The ungrounded configuration enables independent frequency tuning without the decoherence issues of grounded designs.
3Power
If direct coupling between resonators is added to the indirect coupling, then the coupling strength is enhanced, but the circuit complexity increases
Solution Approach 1:
The patent combines direct coupling (through shared capacitor) and indirect coupling (through ungrounded superconducting islands with Josephson junctions) into a unified circuit architecture. This merging provides enhanced coupling strength through multiple pathways while the shared capacitor and common flux bias line keep the overall circuit complexity manageable. The dual coupling mechanism achieves strong interactions without proportionally increasing circuit elements.
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
Enhances control over resonator interactions, improves design and operation simplicity, reduces gate errors, and increases computational accuracy and speed in quantum computing apparatuses.
Implementation Method 1
The indirect coupling comprises: (i) a first coupling between the first resonator and the first superconducting island, (ii) 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.