Weakly Tunable Qubit Design for Flux Noise Reduction
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Solution Overview
Problem
Existing superconducting qubits face challenges in achieving precise frequency tuning without increasing sensitivity to noise and defects, particularly due to limitations in junction size, capacitance, and two-level system defects, which affect coherence times and fabrication complexity.
Innovation Solution
A weakly tunable qubit design is created by coupling a fixed frequency transmon qubit with a tunable frequency transmon qubit, using an asymmetric dc-SQUID shunted by a smaller capacitor, allowing for sub-100 MHz tuning range without excessive junction sizes, thereby reducing sensitivity to flux noise and maintaining coherence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a tunable frequency transmon qubit is used to achieve frequency tuning, then frequency adaptability is improved, but sensitivity to flux noise increases
Solution Approach 1:
The qubit system is segmented into two coupled transmon qubits with distinct frequency characteristics (fixed and tunable), where each segment contributes differently to the overall frequency control and noise response
Solution Approach 2:
The coupling between the two transmon qubits is designed to be asymmetric in its frequency response, with the fixed frequency transmon providing stability and the tunable transmon providing adaptability, creating an asymmetric division of functional roles
2Reliability
If larger junction sizes are used to increase capacitance, then charge dispersion is reduced, but fabrication complexity increases
Solution Approach 1:
The patent combines the capacitance contributions from multiple junctions and capacitors to achieve the required total capacitance value, avoiding the need for single large junctions that would be difficult to fabricate
3Adaptability or versatility
If excessive junction sizes are used to achieve tuning range, then frequency tunability is improved, but sensitivity to two-level system defects increases
Solution Approach 1:
The total junction area is segmented into multiple smaller junctions that collectively provide the required tuning range while individually maintaining low defect sensitivity
Solution Approach 2:
Different regions of the qubit structure (different junctions) are designed with different local properties, where some junctions are optimized for tuning while others are optimized for low defect sensitivity
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 achieves a reduced tunable range, minimizing frequency collisions and noise sensitivity, while maintaining qubit frequency stability and coherence, allowing for reliable fabrication and operation within the 4-5 GHz range with moderate anharmonicity and small charge dispersion.
Implementation Method 1
providing a single Josephson junction (JJ) shunted by a first capacitor, and providing an asymmetric direct current superconducting quantum interference device (dc-SQUID) shunted by a second capacitor
Implementation Method 2
The single JJ is connected to the dc-SQUID through one shared node
Data Source
AI summary
A technique relates to providing a superconducting quantum device. A fixed frequency transmon qubit is provided. A tunable frequency transmon qubit is provided. The fixed frequency transmon qubit is coupled to the tunable frequency transmon qubit to form a single qubit.