Josephson LC Coupler for Tunable Qubit Coupling Control
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Solution Overview
Problem
Existing calculating devices with multiple nonlinear resonators face challenges in controllability, particularly in adjusting coupling strength and resonant frequencies, which affects the precision and efficiency of quantum calculations.
Innovation Solution
A coupler is designed with LC circuits and Josephson junctions, allowing for adjustable magnetic flux to control coupling strength and resonant frequencies, enabling strong coupling and decoupling of nonlinear resonators, thereby improving controllability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If only inductors are used in the coupler design, then the device complexity is reduced, but the controllability and coupling strength between nonlinear resonators deteriorate
Solution Approach 1:
The patent changes the physical parameters of the coupler by incorporating capacitors alongside inductors to form LC circuits. This parameter change enables independent control of resonant frequency and coupling strength through electrical parameters (capacitance values, inductance values) rather than being limited to magnetic coupling only, thereby improving controllability without excessive complexity increase
Solution Approach 2:
The coupler is designed with multi-functionality by integrating both inductive and capacitive elements that serve dual purposes: the LC circuits provide both frequency selection and coupling control functions, while the Josephson junction provides both nonlinearity and tunability. This multi-functionality improves adaptability without proportionally increasing device complexity
2Ease of manufacture
If only inductors are used in the coupler design, then the manufacturing is simpler, but the coupling strength between nonlinear resonators is insufficient
Solution Approach 1:
The coupler employs a composite structure combining inductive elements (superconducting loops), capacitive elements (Josephson junctions and parasitic capacitances), and nonlinear elements. This composite approach enables strong coupling strength through the synergistic interaction of different physical mechanisms (magnetic flux coupling, capacitive coupling, Josephson nonlinearity) while maintaining fabrication compatibility with existing superconducting qubit manufacturing processes
3Adaptability or versatility
If magnetic flux modulation is implemented to control coupling strength, then the controllability is improved, but the device complexity increases
Solution Approach 1:
The Josephson junction-based LC circuits provide self-tunability through their intrinsic nonlinear inductance that depends on the magnetic flux through the superconducting loop. The system uses its own quantum mechanical properties (Josephson effect) to enable flux-dependent coupling strength, eliminating the need for external active control mechanisms and reducing overall device complexity while maintaining improved controllability
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 solution enhances the controllability of calculating devices by allowing for precise adjustment of coupling strength and resonant frequencies, facilitating efficient two-qubit gate operations and maintaining stability of qubit frequencies.
Implementation Method 1
a first Josephson junction including a first Josephson junction end portion electrically connected with the first capacitor end portion, and a first Josephson junction other-end portion electrically connected with the second capacitor end portion
Data Source
Figure 1
Figure 2A~2C
Figure 3A~3B
AI summary
According to one embodiment, a coupler includes first to fourth capacitors, first and second inductors, and a first Josephson junction. The first capacitor includes a first capacitor end portion and a first capacitor other-end portion. The first inductor includes a first inductor end portion, and a first inductor other-end portion. The second inductor includes a second inductor end portion, and a second inductor other-end portion. The first Josephson junction includes a first Josephson junction end portion, and a first Josephson junction other-end portion. A space is surrounded with the first inductor, the second inductor, and the first Josephson junction. The third capacitor includes a third capacitor end portion, and a third capacitor other-end portion. The fourth capacitor includes a fourth capacitor end portion, and a fourth capacitor other-end portion.