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Phase-lead controllers are commonly used in various control systems to enhance response speed and stability. Adjusting the brightness on a television screen offers a practical example of phase-lead control. When contrast is enhanced, a phase-lead controller is employed. Mathematically, phase-lead control is identified when the first parameter is smaller than the second.
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Optimal low-depth quantum signal-processing phase estimation.

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Quantum signal processing enhances parameter estimation accuracy beyond classical limits. New algorithms achieve high precision in quantum experiments, overcoming decoherence and errors for improved two-qubit gate learning.

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Area of Science:

  • Quantum Information Science
  • Quantum Computing
  • Quantum Metrology

Background:

  • Quantum effects like entanglement offer enhanced parameter estimation accuracy.
  • Decoherence and time-dependent errors limit Heisenberg-limited amplification in quantum systems.

Purpose of the Study:

  • Introduce robust Quantum Signal-Processing Phase Estimation algorithms.
  • Achieve optimal quantum parameter estimation performance beyond classical limits.
  • Mitigate challenges posed by decoherence and time-dependent errors.

Main Methods:

  • Employ quantum signal transformation to decouple phase parameters.
  • Utilize provably optimal classical estimation techniques.
  • Combine with near-optimal quantum circuit design for low-depth circuits (<10 gates).

Main Results:

  • Achieve standard deviation accuracy of 10-4 radians in estimating unwanted swap angles.
  • Demonstrate up to two orders of magnitude improvement over existing methods.
  • Show algorithm optimality against time-dependent phase errors, with variance scaling faster than Heisenberg limit in the small-depth regime.

Conclusions:

  • Validated against quantum Fisher information, confirming unmatched precision for two-qubit gate learning.
  • Quantum Signal-Processing Phase Estimation algorithms are robust against decoherence and time-dependent errors.
  • The developed protocol significantly advances the precision of quantum parameter estimation.