Mixed Coupling Qubit Resonator Layout
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Solution Overview
Problem
Quantum computer architectures based on superconducting circuits face geometrical constraints and physical crowding due to capacitive coupling of qubits to resonators, limiting the number of qubits that can be coupled and causing unwanted direct stray coupling.
Innovation Solution
Implementing a mixed coupling scheme that uses both inductive and capacitive coupling, allowing qubits to be coupled at locations other than voltage antinodes, with the coupling strength made independent of the coupler location through varying capacitance and mutual inductance, enabling more qubits to be coupled to a single resonator without physical crowding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If capacitive coupling is used to couple qubits to resonator, then coupling strength can be controlled, but geometrical constraints and physical crowding occur limiting the number of qubits
Solution Approach 1:
The patent changes the coupling mechanism from purely capacitive to a hybrid of inductive and capacitive coupling. By adjusting the mutual inductance parameter (through transformer coupling) and capacitance values, the system achieves location-independent coupling strength, allowing qubits to be placed at various positions along the resonator without physical crowding at voltage antinodes.
Solution Approach 2:
The coupling structure serves multiple functions simultaneously: the transformer provides inductive coupling while also having associated capacitance, creating a unified coupling element that can be positioned anywhere along the resonator with controlled coupling strength, eliminating the need for specialized positioning at voltage antinodes.
2Reliability
If qubits are coupled close to voltage antinodes for strong coupling, then coupling strength is maximized, but physical proximity causes unwanted direct stray coupling between qubits
Solution Approach 1:
The transformer acts as an intermediary coupling element between the qubit and resonator. By using magnetic coupling through the transformer, the direct electromagnetic field interaction between nearby qubits is reduced, while the desired coupling to the resonator is maintained through the transformer's mutual inductance with the resonator.
Solution Approach 2:
The patent modifies the coupling parameters by introducing mutual inductance (M) in addition to capacitance (C). The coupling strength formula g ∝ (M/L_q + C_c/C_q)^0.5 allows independent control of coupling strength from position, enabling qubits to be spaced farther apart while maintaining consistent coupling, thereby reducing stray coupling between adjacent qubits.
3Adaptability or versatility
If qubits are coupled at voltage antinodes, then coupling strength is strong, but geometrical constraints limit circuit layout flexibility
Solution Approach 1:
The patent fundamentally changes the coupling parameter dependency by combining inductive (M) and capacitive (C_c) coupling mechanisms. The total coupling strength g ∝ (M/L_q + C_c/C_q)^0.5 can be kept constant by adjusting either M or C_c when qubit position changes, enabling flexible circuit layouts without sacrificing coupling reliability.
Solution Approach 2:
The coupling system becomes dynamically adjustable: the mutual inductance M and capacitance C_c can be tuned to compensate for position variations, allowing the coupling strength to be optimized for any qubit location along the resonator rather than being fixed to specific positions.
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 alleviates geometrical constraints, allows for a greater number of qubits to be coupled, and reduces physical proximity issues, maintaining consistent coupling strength across different locations on the resonator.
Implementation Method 1
qubits are typically coupled capacitively to the bus resonator near its voltage antinodes
Implementation Method 2
the qubit is coupled to the bus resonator via each of a coupling capacitor and a transformer
Data Source
Figure 1~3
Figure 2
AI summary
Quantum systems are provided, including a qubit and a transmission line resonator having an associated resonant wavelength. A coupling capacitor is configured to capacitively couple the qubit to the transmission line resonator. A transformer is configured to inductively couple the qubit to the transmission line resonator. A selected one of an associated capacitance of the coupling capacitor and an associated mutual inductance of the transformer is a function of a location of the qubit along the transmission line resonator.