Phase-Biased Superconducting Qubit Circuit for Coherence and Anharmonicity
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Solution Overview
Problem
Existing superconducting qubits, such as fluxoniums and 0-π-qubits, face challenges in implementation and operation, particularly in achieving fast and accurate quantum logic gates due to poor coherence properties and high anharmonicity, which are exacerbated by noise from charge and magnetic flux.
Innovation Solution
A quantum processing unit is designed with phase-biased linear and non-linear inductive-energy elements, utilizing a distributed-element resonator as a coplanar waveguide resonator with a center superconductor and superconducting ground plane, and a phase-biasing element to cancel quadratic potential energy terms, enhancing anharmonicity and coherence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If charge qubits are used to achieve high anharmonicity for fast single-qubit operations, then operation speed is improved, but coherence time deteriorates due to dephasing from charge noise
Solution Approach 1:
The patent changes the operating parameters by applying a phase bias to the qubit circuit, transforming it from a charge-sensitive regime to a phase-biased regime. This parameter change allows the system to achieve both high anharmonicity (through the nonlinear inductive element) and long coherence times (by operating at a sweet spot where charge noise has minimal effect on the qubit frequency).
Solution Approach 2:
The patent uses a nonlinear inductive element that replicates the beneficial properties of fluxonium qubits (high anharmonicity and noise immunity) without requiring the complex fluxonium circuit architecture. This allows achieving similar performance characteristics with a simplified design that integrates more easily with standard superconducting qubit platforms.
2Reliability
If fluxonium qubits are used to achieve long coherence times and high anharmonicity, then reliability is improved, but device complexity increases making implementation and operation difficult
Solution Approach 1:
The patent merges the beneficial features of different qubit designs into a single hybrid structure. It combines the phase-biasing concept from flux qubits with the nonlinear inductive element from fluxonium qubits, creating a unified design that achieves long coherence times and high anharmonicity without requiring the complex superinductor arrays or nanowire structures of traditional fluxonium implementations.
Solution Approach 2:
The patent introduces local nonlinearity through a nonlinear inductive element placed at a specific location in the resonator circuit, rather than requiring global circuit complexity. This localized approach to achieving high anharmonicity simplifies the overall device structure while maintaining the desired quantum properties.
3Reliability
If heavy fluxonium qubits are used to protect from magnetic flux noise, then reliability is improved, but operation complexity increases requiring several-photon Raman processes
Solution Approach 1:
The patent uses the phase-biasing mechanism as an intermediary control method that simplifies quantum gate operations. By adjusting the phase bias, the system can directly control qubit transitions without requiring complex multi-photon Raman processes, making quantum gate operations more straightforward while maintaining protection from magnetic flux noise through the nonlinear inductive element.
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 design achieves high anharmonicity and coherence, protecting against low-frequency charge and magnetic flux noise, allowing for longer coherence times and simpler fabrication, thereby improving the performance of quantum computing devices.
Implementation Method 1
a phase-biasing element configured to bias a superconducting phase difference across the linear inductive-energy element and the non-linear inductive-energy element generating and threading a magnetic field through the at least one gap of the distributed-element resonator
Implementation Method 2
a non-linear inductive-energy element including at least one Josephson junction embedded in the CPW resonator
Implementation Method 3
a quantum processing unit comprises a dielectric substrate and at least one superconducting qubit provided on the dielectric substrate. Each of the at least one superconducting qubit comprises a distributed-element resonator comprising at least two conductors separated by at least one gap, wherein the distributed-element resonator is configured as a coplanar waveguide resonator
Data Source
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AI summary
The invention is generally related to the field of quantum computing and particularly to a quantum processing unit comprising at least one superconducting qubit based on phase-biased linear and non-linear inductive-energy elements. A superconducting phase difference across the linear and non-linear inductive-energy elements is biased, for example, by an external magnetic field, such that quadratic potential energy terms of the linear and non-linear inductive-energy elements are cancelled at least partly. In a preferred embodiment, such cancellation is at least 30%. By so doing, it is possible to implement a high-coherence high-anharmonicity superconducting qubit design.