Coplanar Superconducting Tunable Coupler for Parasitic Mode Suppression
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Solution Overview
Problem
Conventional superconducting tunable couplers in coplanar microwave integrated circuits face challenges with parasitic mode propagation due to unequal ground potentials, which are not effectively suppressed by air bridges or wire bonds, limiting their effectiveness and coherence in qubit systems.
Innovation Solution
A coplanar superconducting tunable coupler design that establishes a direct connection between ground plane regions using lumped-element inductances, allowing for variable inductance coupling between qubits, thereby controlling coupling strength and maintaining equipotential between ground planes, eliminating the need for external structures like air bridges or wire bonds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If air bridges or wire bonds are used to suppress parasitic mode propagation, then parasitic mode suppression is improved, but device complexity and manufacturing difficulty increase due to requiring external structures not available in all 2D fabrication processes
Solution Approach 1:
The ground connection function is merged with the signal transmission path by using the coplanar waveguide structure itself to provide both signal routing and ground reference in the same planar layer, eliminating the need for separate air bridges or wire bonds
Solution Approach 2:
The harmful function of external ground connection structures (air bridges, wire bonds) is extracted and replaced by integrating the ground connection function directly into the coplanar waveguide structure, removing the need for separate suppression components
2Reliability
If wire bonds are used to connect ground sections, then ground connection is achieved, but inductance increases significantly compared to continuous ground plane metal interconnect
Solution Approach 1:
The ground connection path is merged with the signal transmission path in the coplanar waveguide structure, where the ground plane regions are electrically connected through the same planar metal layers that carry the signal, achieving low-inductance connection without separate ground wires
3Object-affected harmful factors
If asymmetric placement of air bridges is used, then parasitic mode suppression may be achieved, but manufacturing precision requirements increase and coherence is reduced
Solution Approach 1:
The coplanar waveguide structure maintains equipotential ground regions through its inherent symmetric geometry, where both ground planes are held at the same electrical potential by the continuous metal interconnect, naturally suppressing parasitic modes without requiring precise asymmetric placement
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 design enhances signal integrity by mitigating parasitic mode propagation and maintaining stable DC grounds, improving qubit coherence and coupling control between superconducting devices, and allowing for intermediate coupling states without destroying state information.
Implementation Method 1
a variable inductance coupling element coupled between the first port and the second port
Implementation Method 2
a first termination inductor having a first end coupled to a first end of the variable inductance element and a second end coupled to the first ground plane region
Data Source
Figure 1
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AI summary
A superconducting system is provided that includes a coplanar superconducting circuit. The coplanar superconducting circuit includes a first ground plane region, a second ground plane region electrically isolated from the first ground plane region by portions of the coplanar superconducting circuit, and a tunable coupler having a first port and a second port. The tunable coupler comprises a variable inductance coupling element coupled between the first port and the second port, a first termination inductor having a first end coupled between a first end of the variable inductance element and a second end coupled to the first ground plane region, and a second termination inductor having a first end coupled between a second end of the variable inductance element and a second end coupled to the second ground plane region.