Sarfraj Fency | Searcharxiv

arXiv2026

Optimal enhancement of the Overhauser and Solid Effects within a unified framework

The Overhauser effect (OE) and the Solid effect (SE) are two Dynamic Nuclear Polarization techniques. These two-spin techniques are widely used to create nonequilibrium nuclear spin states having polarization far beyond its equilibrium value. OE is commonly encountered in liquids, and SE is a solid-state technique. Here, we report a single framework based on a recently proposed quantum master equation, to explain both OE and SE. To this end, we use a fluctuation-regularized quantum master equation that predicts dipolar relaxation and drive-induced dissipation, in addition to the standard environmental dissipation channels. Importantly, this unified approach predicts the existence of optimal microwave drive amplitudes that maximize the OE and SE enhancements. We also report optimal enhancement regime for electron-nuclear coupling for maximal enhancement.

quant-ph↗

arXiv2025

Quantum Speed Limit and Optimal Evolution Time in Driven-dissipative Systems

Quantum Speed Limit (QSL) is a lower bound on the evolution time $T_{\rm QSL}$ of a closed quantum system to evolve from one state to another, as shown by Mandelstam and Tamm. For a driving Hamiltonian enforcing the evolution, the time-energy uncertainty relations for the drive play the dominant role in setting the bound. On the other hand, dissipative systems can also suffer from drive-induced dissipation (DID). In this work, we ask how DID modifies the attainability of the QSL in open quantum systems and whether the time-energy uncertainty relation remains the dominating factor. For open quantum systems that suffer from DID, we report a finite optimal evolution time $T_{\rm DID} \; (> T_{\rm QSL})$ for constant-amplitude driving. We show that the competition between DID at short times and environmental dissipation at long times produces a non-monotonic dependence of fidelity on the evolution time. When the drive waveform is shaped using quantum optimal control (QOC), an intermediate attainable evolution time $T_{\rm QOC}$ provides the maximum fidelity. Our results therefore suggest that, in driven-dissipative systems, the conventional QSL lower bound should be complemented by a finite-time attainability window determined by dissipation, with $T_{\rm QSL} \le T_{\rm QOC} \le T_{\rm DID}$ for the cases studied here. Further, we show that the optimized control protocol is robust against detuning and variations in environmental parameters, enabling reliable quantum control in open systems and providing a practical route toward high-fidelity state transfer in two-level quantum systems.

quant-ph↗