Beyond Heisenberg Limit Quantum Metrology through Quantum Signal Processing

• URL: http://arxiv.org/abs/2209.11207v1
• Date: Thu, 22 Sep 2022 17:47:21 GMT
• Title: Beyond Heisenberg Limit Quantum Metrology through Quantum Signal Processing
• Authors: Yulong Dong, Jonathan Gross, Murphy Yuezhen Niu
• Abstract summary: We propose a quantum-signal-processing framework to overcome noise-induced limitations in quantum metrology. Our algorithm achieves an accuracy of $10-4$ radians in standard deviation for learning $theta$ in superconductingqubit experiments. Our work is the first quantum-signal-processing algorithm that demonstrates practical application in laboratory quantum computers.
• Score: 0.0
• License: http://creativecommons.org/licenses/by-nc-nd/4.0/
• Abstract: Leveraging quantum effects in metrology such as entanglement and coherence allows one to measure parameters with enhanced sensitivity. However, time-dependent noise can disrupt such Heisenberg-limited amplification. We propose a quantum-metrology method based on the quantum-signal-processing framework to overcome these realistic noise-induced limitations in practical quantum metrology. Our algorithm separates the gate parameter $\varphi$~(single-qubit Z phase) that is susceptible to time-dependent error from the target gate parameter $\theta$~(swap-angle between |10> and |01> states) that is largely free of time-dependent error. Our method achieves an accuracy of $10^{-4}$ radians in standard deviation for learning $\theta$ in superconducting-qubit experiments, outperforming existing alternative schemes by two orders of magnitude. We also demonstrate the increased robustness in learning time-dependent gate parameters through fast Fourier transformation and sequential phase difference. We show both theoretically and numerically that there is an interesting transition of the optimal metrology variance scaling as a function of circuit depth $d$ from the pre-asymptotic regime $d \ll 1/\theta$ to Heisenberg limit $d \to \infty$. Remarkably, in the pre-asymptotic regime our method's estimation variance on time-sensitive parameter $\varphi$ scales faster than the asymptotic Heisenberg limit as a function of depth, $\text{Var}(\hat{\varphi})\approx 1/d^4$. Our work is the first quantum-signal-processing algorithm that demonstrates practical application in laboratory quantum computers.

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