ZZ-Rotation Qubit Gates With Echo Pulses for Oscillating Error Suppression
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Solution Overview
Problem
Existing quantum computing technologies face significant challenges in suppressing oscillating errors during quantum gate operations, particularly in superconducting qubits, which complicate error suppression protocols and introduce new errors, making them inefficient.
Innovation Solution
A method involving mid-resonance (MR) quantum gates is employed, utilizing rotation and echo pulses with specific frequencies and phases to eliminate oscillating errors, ensuring the ZZ-rotation quantum gate is less noisy than conventional CR gates, and incorporating dynamical decoupling to remove single-qubit Z-rotations and other unwanted fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional cross-resonance (CR) gates are used for ZZ-rotation, then the gate can be implemented with simple control pulses, but oscillating errors (coherent errors including XX and YY rotations) are introduced that reduce gate fidelity
Solution Approach 1:
The patent applies periodic echo pulses at specific frequencies to counteract the oscillating errors generated by CR gates. These echo pulses are applied periodically during and after the gate operation to suppress coherent errors through dynamical decoupling, thereby improving gate fidelity without complicating the basic gate implementation
Solution Approach 2:
The patent modifies the control parameters by introducing echo pulses with specific frequencies and phases that are tuned to counteract the oscillating errors. By changing the temporal and spectral parameters of the control pulses, the system suppresses coherent errors while maintaining the simplicity of the underlying CR gate mechanism
2Reliability
If echo pulses are added to suppress oscillating errors, then gate fidelity is improved, but the circuit depth and number of pulses increase
Solution Approach 1:
The patent applies a limited number of echo pulses that are sufficient to suppress the dominant oscillating errors without over-engineering the solution. By applying just enough correction to achieve the desired fidelity improvement, the circuit depth increase is minimized while still obtaining significant error suppression
3Reliability
If multiple distinct circuits are used for error suppression, then coherent errors are reduced, but the total number of shots required increases
Solution Approach 1:
The patent combines the error suppression functionality with the gate operation itself by integrating echo pulses into the gate sequence. This merging allows the gate to simultaneously perform its computational function and suppress coherent errors, eliminating the need for separate error suppression circuits and reducing the total number of shots required
Data Source
Figure 1A~1B
Figure 2~3
Figure 4A~4B
AI summary
A method for performing a ZZ-rotation quantum gate acting on two qubits having an XX coupling and corresponding resonance frequencies. The method includes applying twice the following pulses: rotation pulses, and echo pulses. In each application of pulses, to each of the two qubits, a corresponding rotation pulse is applied. The rotation pulse has a corresponding phase, has a corresponding amplitude, and has a driving frequency ω^((i) ) distinct from each of the resonance frequencies, so that each of the two qubits is having a corresponding detuning Δ_0,1^((i) ). The echo pulse is commuting with a Pauli-ZZ operator associated with the two qubits. The echo pulse is applied so as to control a magnitude of any one of: XX+θ(Δ_0^((i) ) Δ_1^((i) ) )·YY rotation, and XY-θ(Δ_0^((i) ) Δ_1^((i) ) )·YX rotation. In each application of pulses, the echo pulse is applied after the rotation pulse.