Gustavo Fernandes da Costa

arXiv2026

Reverse engineering of single-qubit quantum gates

In this work, we address the problem of designing single-qubit quantum gates by means of a linearly-polarized field. We show that any desired one-qubit gate corresponding to a special unitary matrix can be generated by a modulated sinusoidal field. The only approximation involved is the rotating-wave-approximation. The formula for the control field is obtained by inverting the equation of motion for the evolution operator and imposing the conditions for the desired gate. We give a simple procedure to obtain closed analytical formulas for the fields in terms of a priori chosen dynamical functions. Additionally, these dynamical functions can depend on tunable free parameters intentionally introduced to meet a desired performance criteria.

quant-ph↗

arXiv2025

Simultaneous control of populations and coherence phase of open two-level quantum systems with a single pulse

We address the control of the dynamics of both population and coherence phase in an open two-level quantum system employing a single external control field. The system dynamics is described by a Markovian master equation that takes into account dephasing and thermal noise. The control is engineered by inverting the underlying equations of motion, which yields an analytical expression for the control field in terms of user-specified time-dependent functions for the population and coherence phase. Our approach allows to dictate not only the initial and final populations and phases, but the full dynamics of these quantities. The chosen functions for population and phase have to conform to certain constraints indicated in our analysis. Our methodology also reveals the possible transitions for given initial conditions and environmental noise parameters.

quant-ph↗