Persistent Current Qubit Reset Using Resonant Microwave Driving
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Solution Overview
Problem
Current methods for preparing persistent current qubits in a well-defined initial state introduce broadband noise and decoherence due to the need for high-bandwidth flux bias lines, which destabilize the excited state and require lengthy decay times.
Innovation Solution
A microwave-based reset method using a superconducting loop with a compound Josephson junction, where bias sources adjust the qubit's potential to position an excited state near a potential barrier, allowing a continuous microwave signal to transition the qubit from an excited state to the ground state, reducing noise and decoherence by using low-pass filtered DC flux bias lines and narrowband microwave drives.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large DC flux shift is applied to destabilize the excited state, then the qubit can be prepared in the ground state, but broadband noise is introduced causing decoherence
Solution Approach 1:
The patent applies periodic microwave pulses at the qubit's transition frequency to induce controlled transitions between energy states. This periodic action allows the qubit to be reset to the ground state through resonant driving, avoiding the need for large DC flux shifts that generate broadband noise. The microwave-based approach provides a cleaner, more selective method for state preparation.
Solution Approach 2:
The patent replaces the mechanical/electrical approach of using large DC flux shifts with a microwave electromagnetic field approach. By substituting the DC flux method with microwave-driven transitions, the system achieves ground state preparation without introducing broadband noise, thereby reducing decoherence while maintaining preparation fidelity.
2Productivity
If high-bandwidth flux bias lines are used to apply destabilizing pulses, then excited state destabilization is achieved, but device complexity increases
Solution Approach 1:
The patent substitutes the high-bandwidth flux bias line approach with microwave signal delivery through existing low-pass filtered lines. This replacement eliminates the need for complex high-bandwidth control infrastructure while achieving efficient state preparation through resonant microwave driving, thereby reducing device complexity without sacrificing preparation speed.
Solution Approach 2:
The patent changes the control parameter from large DC flux shifts requiring high bandwidth to microwave frequency signals that can be transmitted through low-pass filtered lines. This parameter change allows the use of simpler, lower-bandwidth control infrastructure while maintaining effective qubit state manipulation and preparation.
3Loss of time
If large DC flux shifts are applied, then excited state decay is accelerated, but noise and decoherence increase
Solution Approach 1:
The patent uses periodic microwave pulses at the qubit's transition frequency to accelerate excited state decay. This resonant periodic driving induces rapid transitions from the excited state to the ground state without requiring large DC flux shifts, thereby reducing the excited state lifetime without introducing broadband noise that would cause decoherence.
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 effectively resets persistent current qubits to the ground state with lower noise and decoherence, enabling high-fidelity quantum operations by utilizing low-pass filtered DC flux bias lines and narrowband microwave drives.
Implementation Method 1
A microwave source generates a continuous microwave signal having a frequency equal to a transition frequency between an other excited state of the qubit and the given excited state
Implementation Method 2
a qubit that includes a superconducting loop interrupted by a compound Josephson junction
Implementation Method 3
A first bias source provides a first bias to the superconducting loop, and a second bias source provides a second bias to the compound Josephson junction
Data Source
AI summary
Systems and methods are provided for resetting a qubit comprising a superconducting loop and a compound Josephson junction. A first bias flux is provided to the superconducting loop. A second bias flux is provided to the compound Josephson junction. Each of the first bias flux and the second bias flux are provided such that a given excited state of the qubit is near a top of a potential barrier associated with a potential of the qubit. A continuous microwave signal is generated having a frequency equal to a transition frequency between an other excited state of the qubit and the given excited state.