Universal Quantum Gate Control with Leakage-Penalized Pulses
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Solution Overview
Problem
Existing quantum computers face challenges in implementing fast and error-free quantum gates due to leakage errors, which hinder the efficient execution of computational tasks.
Innovation Solution
The implementation of a universal control cost function that penalizes leakage errors, runtime, and infidelity, allowing for the optimization of control pulses to reduce leakage errors and improve gate fidelity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If quantum gates are executed faster to increase computational capacity, then productivity improves, but leakage errors increase causing gate fidelity to deteriorate
Solution Approach 1:
The patent changes the parameters of the time-dependent Hamiltonian evolution to optimize the control pulse. By adjusting parameters such as pulse amplitude, duration, and temporal shape, the method achieves fast gate execution while suppressing leakage errors through optimized evolution trajectories that avoid population transfer to non-computational states
Solution Approach 2:
The patent employs a control cost function that includes leakage penalty terms as feedback to guide the optimization process. The leakage penalty term monitors and penalizes population transfer to non-computational states during gate evolution, allowing the optimization algorithm to adjust control parameters to minimize leakage while maintaining fast execution speeds
2Reliability
If control pulses are optimized to reduce leakage errors, then gate fidelity improves, but the complexity of control increases
Solution Approach 1:
The patent develops a universal control framework with a general cost function structure that can optimize multiple objectives simultaneously (leakage reduction, runtime minimization, fidelity improvement) through a single optimization process. This universal approach avoids the need for separate specialized control schemes for different error types, reducing overall control complexity
Solution Approach 2:
The patent introduces a control cost function as an intermediary that translates physical requirements (low leakage, fast execution) into a mathematical optimization problem. This intermediary framework simplifies the control design by providing a systematic method to balance competing requirements without directly managing complex control waveforms
3Loss of time
If the runtime of quantum gates is reduced to increase computational speed, then productivity improves, but leakage errors increase due to non-adiabatic transitions
Solution Approach 1:
The patent employs dynamic control pulses with time-dependent amplitude and phase modulation to achieve fast gate evolution while suppressing leakage. The control Hamiltonian parameters are dynamically adjusted during the gate operation to maintain adiabatic conditions at critical points while enabling rapid overall evolution, balancing speed and leakage suppression
Data Source
AI summary
Methods, systems, and apparatus for implementing a unitary quantum gate on one or more qubits. In one aspect, a method includes the actions designing a control pulse for the unitary quantum gate, comprising: defining a universal quantum control cost function, wherein the control cost function comprises a qubit leakage penalty term representing i) coherent qubit leakage, and ii) incoherent qubit leakage across all frequency components during a time dependent Hamiltonian evolution that realizes the unitary quantum gate; adjusting parameters of the time dependent Hamiltonian evolution to vary a control cost according to the control cost function such that leakage errors are reduced; generating the control pulse using the adjusted parameters; and applying the control pulse to the one or more qubits to implement the unitary quantum gate.