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, leading to reduced performance in two-qubit gates.
Innovation Solution
A tunable resonator-resonator coupling circuit with ungrounded superconducting islands provides direct and indirect couplings, allowing controlled interaction between resonators with different coupling frequencies, reducing decoherence and improving operational efficiency.
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 adversely affects the operation speed and accuracy of two-qubit gates
Solution Approach 1:
The patent inverts the conventional approach by using two ungrounded superconducting islands instead of a single grounded island. This inversion allows the idling frequency to be positioned below the qubit frequencies rather than above them, thereby improving both operation speed and accuracy simultaneously by eliminating the frequency conflict that plagues traditional designs
2Adaptability or versatility
If the tunable coupler is implemented with ungrounded superconducting islands, then the coupling frequency sign can be controlled, but the device complexity increases
Solution Approach 1:
The patent introduces an intermediary element - the second ungrounded superconducting island - that mediates the coupling between resonators. This intermediary enables independent control of coupling frequency signs while the shared ground connection simplifies the overall circuit architecture, balancing complexity with functionality
3Adaptability or versatility
If direct and indirect coupling terms cancel each other at a certain coupler frequency, then the coupling can be tuned to zero, but this cancellation point is at an idling frequency above qubit frequencies which reduces gate performance
Solution Approach 1:
The patent creates an asymmetric coupling configuration where the two ungrounded islands have different coupling arrangements with the resonators. This asymmetry allows the coupling cancellation point to occur at a lower frequency below the qubit frequencies, enabling full coupling tunability from zero to maximum without the performance degradation caused by high-frequency cancellation points in symmetric designs
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 design enhances the accuracy and speed of quantum computing operations by aligning the idling frequency below qubit frequencies, reducing gate errors and resonance interference.
Implementation Method 1
a Josephson coupling between the first superconducting island and the second superconducting island
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 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.