Frequency-Tunable Qubit Coupler Control for Fast, High-Fidelity Gates
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Solution Overview
Problem
Existing methods for implementing two-qubit quantum logic gates, such as controlled-Z (CZ) and swap gates, are inefficient and prone to unwanted swap behavior, leading to low gate fidelity and slow execution times.
Innovation Solution
A control model that includes non-orthogonal controlled-Z and swap operators, along with detuning and frequency shift operators, is used to generate a control signal for implementing two-qubit quantum logic gates, allowing for a sequence of control pulses to efficiently execute these gates with reduced leakage and faster execution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional methods are used to implement two-qubit quantum logic gates, then the implementation is simple, but the gate fidelity is low and execution time is slow
Solution Approach 1:
The patent applies parameter changes by modifying the control signal parameters (amplitude, frequency, phase, duration) to optimize gate fidelity. The control model adjusts parameters such as the strength and timing of microwave pulses applied to qubits, transforming fixed conventional parameters into dynamically optimized variables that maximize gate operation accuracy while maintaining manageable system complexity.
Solution Approach 2:
The patent implements dynamics by introducing a dynamic control model that adapts control signals in real-time based on quantum state evolution. The system dynamically adjusts coupling strengths, detuning parameters, and pulse sequences during gate execution, allowing the control strategy to respond to changing quantum conditions and achieve high fidelity without requiring overly complex static control architectures.
2Speed
If conventional control strategies are used, then the control implementation is straightforward, but the execution time is slow and leakage is high
Solution Approach 1:
The patent applies preliminary action by pre-calculating and optimizing control signal parameters before gate execution. The control model pre-determines optimal pulse sequences, coupling configurations, and detuning schedules based on desired gate operations, allowing the system to execute gates rapidly without real-time computation delays while avoiding the need for overly complex adaptive control circuits.
Solution Approach 2:
The patent implements skipping by using optimized control pulses that rapidly drive quantum transitions in minimal time. The control model employs shaped microwave pulses with optimized rise/fall times and amplitude profiles that accomplish qubit rotations and gate operations faster than conventional square pulses, reducing execution time and minimizing exposure to decoherence and leakage errors.
3Reliability
If standard controlled-Z and swap operators are used, then the operators are orthogonal and easy to implement, but unwanted swap behavior occurs and fidelity decreases
Solution Approach 1:
The patent applies asymmetry by using non-orthogonal controlled-Z and swap operators that have asymmetric coupling configurations and detuning parameters. This asymmetric design allows the control model to distinguish between desired gate operations and unwanted swap behavior, enabling selective suppression of harmful effects while maintaining ease of implementation through a unified control framework that handles both operator types systematically.
4Speed
If faster gate execution is attempted, then speed improves, but accuracy and fidelity decrease due to leakage
Solution Approach 1:
The patent applies periodic action by using oscillating control pulses with carefully selected frequencies and durations. The control model employs periodic microwave drive sequences that resonate with qubit transition frequencies, enabling fast gate operations through coherent driven evolution. The periodic nature of these pulses maintains quantum coherence and minimizes leakage to non-computational states while achieving high-speed operation.
Solution Approach 2:
The patent implements continuity of useful action by using smooth, continuous control pulses rather than abrupt discontinuous switches. The control model employs adiabatic pulse shaping and continuous frequency modulation that maintains continuous coupling between control fields and qubits throughout the gate operation, preventing energy leakage and maintaining high fidelity even during fast operations. This continuous control approach eliminates gaps where decoherence and leakage could occur.
Data Source
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AI summary
Methods, systems and apparatus for implementing a target two-qubit quantum logic gate on a first qubit and second qubit using a tunable qubit coupler. In one aspect, a method includes generating a control signal for the target two-qubit quantum logic gate according to a control model, wherein the control model comprises a controlled-Z operator and a swap operator that are non-orthogonal; and applying the control signal to the first qubit, second qubit and tunable qubit coupler.