Compound Josephson Junction Tuning for Uniform Qubit Behavior
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Solution Overview
Problem
Superconducting quantum processors face issues due to unwanted discrepancies in the elements, such as Josephson junction asymmetry and variations in qubit capacitance and inductance, resulting from fabrication imperfections, which affect the behavior and interaction of devices.
Innovation Solution
The implementation of a circuit structure with primary and secondary compound Josephson junctions, tunable capacitance through series LC-circuits, and dedicated tunable couplers to actively compensate for these discrepancies, allowing for the alignment of qubit characteristics and synchronization of qubit behavior.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If compound Josephson junction structures are used to compensate for fabrication discrepancies, then uniformity of qubit characteristics is improved, but device complexity increases
Solution Approach 1:
The Josephson junction is divided into multiple sub-junctions arranged in parallel within a compound structure. Each sub-junction can be independently tuned, allowing compensation for fabrication variations while maintaining overall functionality. This segmentation enables precise control of critical current to achieve uniform qubit characteristics across the processor.
Solution Approach 2:
The compound Josephson junction structure incorporates tunable elements that allow dynamic adjustment of electrical characteristics during or after fabrication. By applying external control signals, the critical current and other parameters can be fine-tuned to compensate for manufacturing discrepancies, transforming a static structure into a dynamically adjustable one.
2Reliability
If multiple Josephson junctions are implemented in series or parallel to achieve desired electrical characteristics, then qubit performance is improved, but fabrication precision requirements increase
Solution Approach 1:
Instead of relying solely on precise fabrication of single junctions, the invention changes the approach by using multiple junctions whose combined parameters can be adjusted through tuning mechanisms. The critical current, capacitance, and inductance parameters can be modified post-fabrication to achieve desired qubit performance even when individual junction parameters vary due to fabrication tolerances.
Solution Approach 2:
The system incorporates measurement and feedback mechanisms that allow characterization of actual junction parameters after fabrication. Based on measured deviations from target values, control signals are adjusted to compensate for discrepancies, creating a feedback loop that ensures qubit performance meets specifications despite manufacturing variations.
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 approach enables active compensation for Josephson junction asymmetry, qubit capacitance, and inductance variations, ensuring consistent qubit behavior and improving the performance of superconducting quantum processors by tuning parameters to desired levels.
Implementation Method 1
a primary compound Josephson junction structure comprising two parallel current paths that are each formed of a material that is superconducting below a critical temperature, wherein each of the two parallel current paths of the primary compound Josephson junction structure includes a respective Josephson junction structure
Implementation Method 2
two parallel current paths that are each formed of a material that is superconducting below a critical temperature
Data Source
AI summary
Apparatus and methods enable active compensation for unwanted discrepancies in the superconducting elements of a quantum processor. A qubit may include a primary compound Josephson junction (CJJ) structure, which may include at least a first secondary CJJ structure to enable compensation for Josephson junction asymmetry in the primary CJJ structure. A qubit may include a series LC-circuit coupled in parallel with a first CJJ structure to provide a tunable capacitance. A qubit control system may include means for tuning inductance of a qubit loop, for instance a tunable coupler inductively coupled to the qubit loop and controlled by a programming interface, or a CJJ structure coupled in series with the qubit loop and controlled by a programming interface.