Dielectric Thinning for Quantum Device Stray Coupling
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Solution Overview
Problem
Quantum devices face challenges with surface loss and stray coupling due to interactions with two-level systems on surfaces and interfaces, which affect the quality factor and coherence of qubits, especially in superconducting quantum circuits where deposited dielectrics exhibit significant loss and undesired capacitive coupling.
Innovation Solution
The approach involves dielectric thinning of the substrate on which co-planar quantum circuit elements are formed, reducing the effective dielectric constant associated with stray capacitive coupling by decreasing the substrate thickness, thereby reducing surface loss and stray coupling without altering the capacitive coupling to desired elements, by setting the effective dielectric constant above a first threshold for nearest neighbors and below a second threshold for next-nearest neighbors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the substrate thickness is decreased to reduce surface loss and stray coupling, then the effective dielectric constant for next-nearest-neighbor coupling is reduced below a second threshold, but the effective dielectric constant for nearest-neighbor coupling must be maintained above a first threshold
Solution Approach 1:
The patent applies local quality by creating a non-uniform substrate thickness profile where different regions have different thicknesses. Specifically, the substrate is thinner in regions where reduced dielectric constant is desired (to minimize stray coupling to next-nearest neighbors) while maintaining adequate thickness in other regions. This spatial variation in substrate thickness allows simultaneous optimization of nearest-neighbor coupling (maintaining effective dielectric constant above first threshold) and next-nearest-neighbor isolation (reducing effective dielectric constant below second threshold).
Solution Approach 2:
The patent employs parameter changes by modifying the substrate thickness parameter to control the effective dielectric constant. By adjusting the substrate thickness from a conventional uniform value to a reduced non-uniform profile, the effective dielectric constant experienced by different co-planar structures is changed. This parameter modification enables the system to achieve distinct effective dielectric constants for nearest-neighbor and next-nearest-neighbor interactions, resolving the contradiction between maintaining strong desired coupling and minimizing unwanted coupling.
2Object-generated harmful factors
If the substrate thickness is reduced to minimize capacitive coupling to next-nearest neighbors, then stray coupling is reduced, but the capacitive coupling to nearest-neighbor elements must be preserved
Solution Approach 1:
The patent implements local quality by positioning thinner substrate regions selectively beneath or adjacent to specific co-planar structures. This localized thinning creates spatially varying effective dielectric constants that differentially affect coupling strengths. Structures requiring strong coupling to nearest neighbors are positioned where the substrate thickness maintains adequate dielectric constant, while structures prone to unwanted next-nearest-neighbor coupling are positioned over thinner substrate regions where the effective dielectric constant is reduced.
Solution Approach 2:
The substrate acts as an intermediary element whose thickness is modulated to control coupling interactions. By varying the substrate thickness, the patent mediates the capacitive coupling between co-planar structures and the underlying environment. The substrate thickness serves as a control parameter that can be adjusted to achieve desired coupling strengths, allowing the system to simultaneously maintain strong nearest-neighbor coupling while reducing next-nearest-neighbor stray coupling through its position-dependent dielectric properties.
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 method effectively reduces surface loss and stray coupling, improving the quality factor and coherence of qubits by minimizing unwanted interactions, allowing for more efficient operation of quantum processors with reduced phase errors and decoherence.
Implementation Method 1
reducing the effective dielectric constant associated with stray capacitive coupling by decreasing the substrate thickness
Implementation Method 2
each co-planar structure, of the at least three co-planar structures, including a superconductor
Data Source
AI summary
A quantum device includes: a substrate; and at least three co-planar structures arranged on a surface of the substrate, each co-planar structure, of the at least three co-planar structures, including a superconductor, in which a first effective dielectric constant between a first co-planar structure and a second co-planar structure that is a nearest neighbor to the first co-planar structure is above a first threshold, a second effective dielectric constant between the first co-planar structure and a third co-planar structure that is a next nearest neighbor to the first so-planar structure is less than a second threshold, and the second threshold is less than the first threshold.