Noise-Robust Ultrafast Entanglement Generation in Rydberg Atoms via Quantum Optimal Control

TL;DR

This paper analyzes the effects of laser noise on ultrafast entanglement generation in Rydberg atoms, demonstrating that optimized control pulses can achieve high fidelity despite realistic noise conditions.

Contribution

It introduces quantum optimal control strategies to mitigate laser noise effects, achieving near-perfect entanglement fidelity in ultrafast Rydberg atom systems.

Findings

Amplitude noise tolerates up to 30% with >90% fidelity

Phase noise causes rapid fidelity decline beyond 1% noise

Optimized pulses with spectral notches reach 99% fidelity in noise-free conditions

Abstract

We present a comprehensive theoretical analysis of ultrafast entanglement generation between two Rydberg-blockaded atoms, explicitly accounting for realistic laser noise. Using femtosecond Gaussian pulses as a baseline, we systematically evaluate Bell-state fidelity sensitivity to amplitude and phase noise across white, pink (1/f), and Ornstein-Uhlenbeck spectra using Monte Carlo ensemble simulations. Our results show that amplitude noise is well tolerated, with fidelities above 90% even at 30% noise levels, while phase noise is the primary limiting factor, causing fidelity to drop rapidly beyond about 1% noise amplitude. The spectral structure of the noise is also important: pink noise consistently causes less fidelity loss than white noise of the same amplitude. By applying quantum optimal control theory (QOCT) with the D-MORPH algorithm under multiple equality constraints, we obtain a double-pulse structure with a spectral notch that achieves approximately 99% fidelity in the noise-free case and maintains high fidelity under moderate amplitude noise. A breakdown threshold near 1% amplitude noise is identified, beyond which even optimized pulses cannot sustain coherent control. These results offer practical benchmarks for the development of ultrafast neutral-atom quantum processors operating in the femtosecond regime.