Vacuum-Bridged Josephson Junctions for Reduced Qubit Interface Loss
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Solution Overview
Problem
Losses at interfaces between different materials in superconducting devices, particularly Josephson junctions, lead to reduced performance and coherence time in qubits, such as transmon qubits, due to parasitic effects.
Innovation Solution
The integration of bridge connections between the Josephson junction and external electrodes, formed using a method involving resist patterning and superconducting thin film deposition, ensures that no part of the Josephson junction is in direct contact with the electrodes, thereby minimizing parasitic effects and reducing interface losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the Josephson junction is directly connected to external electrodes, then the device complexity is reduced, but interface losses increase leading to lower qubit coherence time
Solution Approach 1:
Bridge connections are introduced as intermediary elements between the Josephson junction and external electrodes. These bridges are formed of superconducting material and connect to the Josephson junction at contact pads, providing an indirect connection path that eliminates direct contact between the junction and external electrodes, thereby reducing interface losses and improving coherence time
Solution Approach 2:
The connection path is segmented into distinct components: the Josephson junction, bridge connections, and external electrodes. The bridge connections are separated from the substrate using sacrificial sacrificial oxide layers, creating spatial segmentation that isolates the Josephson junction from lossy interfaces with external electrodes while maintaining electrical connectivity
2Reliability
If bridge connections are introduced to reduce interface losses, then qubit performance improves, but the fabrication process complexity increases
Solution Approach 1:
Contact pads are pre-formed on the Josephson junction during the junction fabrication process itself, before the bridge connections are created. The sacrificial oxide layers are also deposited in advance, preparing the structure for subsequent bridge formation and lift-off processes
Solution Approach 2:
Traditional direct mechanical/electrical contact is replaced with a suspended bridge structure. The bridges are formed using deposition and lift-off techniques, and the sacrificial oxide layers are removed through chemical etching, substituting direct contact with a more complex but lower-loss indirect connection
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 configuration enhances the performance and coherence time of superconducting qubits by reducing parasitic effects and interface losses, leading to improved operational efficiency in quantum processing units.
Implementation Method 1
superconducting devices including Josephson junctions
Implementation Method 2
depositing a superconducting thin film over the resist
Data Source
Figure 1
Figure 2A~2B
Figure 3A~3B
AI summary
The invention relates to the field of superconducting integrated circuits. The invention includes an integrated circuit device comprising a substrate (201), a Josephson junction (210) on the substrate (201), external electrodes (202 a,b) on the substrate (201) and spaced apart from the Josephson junction (210), and bridge connections (502 a,b) connecting the Josephson junction (210) to the external electrodes (202 a,b). The invention also includes a method for manufacturing such an integrated circuit device.