Cap Wafer Quantum Circuits for Qubit Isolation and Low Microwave Loss
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Solution Overview
Problem
Existing quantum computing architectures face challenges with noise-induced errors, unwanted cross-coupling between qubits, thermal isolation issues, and microwave loss, which affect qubit device performance and coherence time.
Innovation Solution
The implementation of cap wafer architectures with via designs and interposers in microwave integrated quantum circuits, which provide improved thermal isolation, controlled coupling, and reduced electromagnetic interference, while suppressing unwanted cross-coupling and microwave loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If superconducting qubits are implemented in quantum circuits, then quantum computational capability is achieved, but noise-induced errors and reduced coherence time occur
Solution Approach 1:
A cap wafer is introduced as an intermediary component between the quantum circuit substrate and the external environment. The cap wafer contains recesses that form enclosures around quantum circuit devices, acting as a protective intermediary that shields qubits from noise while maintaining controlled coupling between adjacent qubits through precisely engineered via structures.
Solution Approach 2:
The quantum computing system is segmented into distinct functional layers: a substrate layer containing quantum circuit devices, a cap wafer layer with recesses forming individual enclosures, and via structures connecting the layers. This segmentation isolates each quantum circuit device within its own enclosure, reducing cross-talk and noise while maintaining system functionality.
2Productivity
If multiple qubit devices are integrated in quantum circuits, then quantum processing capability is enhanced, but unwanted cross-coupling between qubit devices increases
Solution Approach 1:
Each qubit device is enclosed in a separate recess within the cap wafer, physically segmenting the quantum circuit into isolated units. This segmentation prevents unwanted electromagnetic coupling between adjacent qubits while allowing controlled coupling through specifically designed via structures that connect only intended qubit pairs.
Solution Approach 2:
The cap wafer provides different functional properties in different locations: recesses provide isolation for individual qubits, while via structures provide controlled coupling pathways. This local differentiation of structural properties enables simultaneous achievement of isolation and controlled interaction where needed.
3Reliability
If conventional via designs are used in quantum circuits, then electrical connectivity is achieved, but thermal isolation is insufficient and microwave loss increases
Solution Approach 1:
Via structures serve as intermediary elements that simultaneously provide electrical connectivity between the substrate and cap wafer while maintaining thermal isolation. The vias are precisely engineered to allow microwave signals to pass through with minimal loss while blocking thermal conduction paths from the warmer cap wafer to the colder quantum circuit devices.
Solution Approach 2:
The via structures are designed with specific geometric parameters (size, shape, material composition) that change their electromagnetic and thermal properties. These parameter optimizations enable the vias to transmit microwave signals efficiently while minimizing thermal conduction, resolving the contradiction between electrical connectivity and thermal isolation.
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 qubit device performance by improving coherence time, reducing unwanted coupling, and providing scalable, mechanically robust quantum computing systems with enhanced thermal isolation and signal integrity.
Implementation Method 1
each recess is configured to suppress propagation inside the recess of electromagnetic waves that have frequencies below a cutoff frequency, the cutoff frequency being larger than an operating frequency of the quantum circuit device
Implementation Method 2
vias containing normally-conducting metals (e.g., copper) may operate as excellent heat sinks for for superconducting signal lines
Implementation Method 3
The vias include a material that is superconducting during operation of the quantum computing system
Data Source
AI summary
A quantum computing system that includes a quantum circuit device having at least one operating frequency; a first substrate having a first surface on which the quantum circuit device is disposed; a second substrate having a first surface that defines a recess of the second substrate, the first and second substrates being arranged such that the recess of the second substrate forms an enclosure that houses the quantum circuit device; and an electrically conducting layer that covers at least a portion of the recess of the second substrate.