Composite Qubit Design with Segmented Josephson Junctions
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Solution Overview
Problem
Existing qubit designs face challenges in resisting decoherence due to external noise, making it difficult to maintain information integrity, and large inductors used for robustness are hard to fabricate and prone to self-resonances.
Innovation Solution
A composite qubit design utilizing concatenated doubly periodic Josephson junction circuits with reduced inductor sizes, typically less than 1 µH, which improves decoherence resistance through exponential reduction in noise sensitivity and simplifies fabrication by using nanowires for inductors and capacitors to enhance dephasing times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If large superinductors (more than 10 μH) are used in 0-π qubit design to provide robustness against decoherence, then the qubit resistance to decoherence is improved, but the fabrication difficulty increases and self-resonance problems occur
Solution Approach 1:
The patent divides the single large superinductor into multiple smaller inductors (typically three inductors with values of 1-10 nH each) connected in series within the bridge circuit. This segmentation achieves the same total inductance value while avoiding the fabrication difficulties and self-resonance issues associated with large single inductors, as each small inductor can be more easily manufactured with controlled characteristics.
Solution Approach 2:
The patent applies different inductor values to different positions within the bridge circuit. The bridge circuit includes first and second inductors with a first value and third and fourth inductors with a second value, where the ratio of these values is a key parameter. This local differentiation optimizes the quantum energy levels and decoherence resistance while maintaining manufacturability of individual components.
2Reliability
If large superinductors (more than 10 μH) are used in 0-π qubit design to provide robustness against decoherence, then the qubit resistance to decoherence is improved, but self-resonance problems occur that prevent practical adoption
Solution Approach 1:
By segmenting the large inductor into multiple small inductors (1-10 nH each) in series, the patent eliminates the self-resonance problems inherent in large single inductors. Each small inductor has a much higher self-resonance frequency, pushing the harmful resonance effects well above the operational frequency range of the qubit, thereby maintaining decoherence resistance without self-resonance interference.
Solution Approach 2:
The patent changes the inductor value parameter from large (10 μH or more) to small (1-10 nH) while compensating by using multiple inductors in series. This parameter transformation maintains the total inductance needed for quantum energy level control while fundamentally changing the resonant characteristics to eliminate harmful self-resonance effects.
3Loss of information
If redundancy techniques are used to detect and correct errors in qubits, then information integrity is improved, but the requirement for threshold level resistance to decoherence makes redundancy impractical without sufficient inherent robustness
Solution Approach 1:
The patent implements preliminary protection by designing the bridge circuit with specific inductor ratios that create quantum energy levels inherently resistant to decoherence. By establishing this robust base level of protection through careful circuit parameter design before applying redundancy techniques, the system creates a foundation that makes redundancy practical and effective, as the qubit already possesses sufficient inherent robustness to maintain information integrity.
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 composite qubit design provides improved resistance to decoherence while being more manufacturable, reducing self-resonance issues and allowing for longer dephasing times, thus maintaining quantum state integrity effectively.
Implementation Method 1
Each doubly periodic Josephson junction circuit employs two Josephson junctions symmetrically arranged in a bridge circuit
Implementation Method 2
The inductors may be fabricated from nanowires selected from the group consisting of disordered silicide or germanium alloys, nitride-based superconductors, and disordered aluminum
Data Source
Figure 1~2
Figure 3
AI summary
A quantum computer architecture employs logical qubits that are constructed from a concatenation of doubly periodic Josephson junction circuits. The series concatenation of the doubly periodic Josephson junction circuits provides exponential robustness against local noise. It is possible to perform discrete Clifford group rotations and entangling operations on the logical qubits without leaving the protected state.