Opposite Anharmonicity Coupler for Quantum Gates
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Solution Overview
Problem
Current quantum computing technologies face challenges in achieving fast and high-fidelity two-qubit gates due to strong-drive effects and cross-Kerr interactions, which lead to decoherence and errors, particularly in scaling up quantum processors.
Innovation Solution
A tunable coupler with opposite anharmonicity to the qubits is used to suppress ZZ crosstalk, enabling fast and high-fidelity entangling gates by modulating the external flux, allowing for gates between far-detuned qubits while minimizing unwanted crosstalk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If strong-drive effects are used to achieve fast two-qubit gates, then gate speed is improved, but cross-Kerr interactions and ZZ terms increase causing decoherence and errors
Solution Approach 1:
A coupler qubit is introduced as an intermediary between the two computational qubits. The coupler mediates the interaction between qubits during gate operations, enabling controlled coupling while maintaining the computational qubits in a non-interacting state during idle periods. This resolves the contradiction by providing a dedicated mediator that enables fast gates when needed while preventing spurious ZZ interactions during storage.
Solution Approach 2:
The system transitions from static qubit-qubit coupling to dynamic coupling control. The coupler's coupling strength is modulated in time: strong coupling is activated only during gate operations, while during idle periods the coupling is minimized. This dynamic control allows the system to achieve fast gates when required while suppressing cross-Kerr interactions during quantum state storage, thereby improving both speed and fidelity.
2Adaptability or versatility
If qubit connectivity is increased to enable more two-qubit gates, then quantum circuit complexity is improved, but ZZ interactions and quantum chaotic behavior increase
Solution Approach 1:
The coupler qubit serves as a mediator that enables versatile quantum circuit operations without requiring direct connectivity between all qubit pairs. By routing interactions through the coupler, the system achieves high circuit complexity while maintaining control over ZZ interactions, as the coupler can be selectively activated only when gate operations are needed.
Solution Approach 2:
The quantum system is segmented into computational qubits and a coupler qubit with distinct functional roles. The computational qubits store quantum information with minimal interactions, while the coupler handles all interaction operations. This segmentation isolates the harmful ZZ interactions to specific gate operation windows, preventing them from accumulating during idle periods and enabling scalable quantum circuits.
3Duration of action of moving object
If gate operation time is reduced to minimize decoherence, then coherence time utilization is improved, but strong-drive effects and beyond-RWA corrections become significant
Solution Approach 1:
The coupler-mediated interaction enables efficient gate operations with reduced duration by providing a dedicated coupling pathway. The coupler's strong coupling to both computational qubits allows for rapid information exchange, achieving fast gates while maintaining better control over drive strengths, thereby reducing beyond-RWA corrections compared to direct strong qubit-qubit coupling.
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 results in significantly faster gate operations, increasing the complexity and depth of quantum circuits, and reducing spectral crowding issues, thereby enhancing the scalability and coherence of quantum processors.
Implementation Method 1
tuning, by applying a flux bias, a coupler to suppress ZZ crosstalk between at least two qubit structures
Implementation Method 2
The flux qubit can comprise four shunting Josephson junctions
Data Source
AI summary
Disclosed herein are methods, systems, and devices including a tunable coupler design that harnesses interference due to higher energy levels to achieve zero static ZZ coupling between the two qubits. Biasing to zero ZZ interaction, a fast perfect entangler is realized with parametric flux modulation in less than 20 ns. The disclosed coupler provides very fast gates between far-detuned fixed frequency qubits, and is a crucial building block in scaled quantum computers.