Optimal control of molecular spin qudits

TL;DR

This paper demonstrates numerically that shaped microwave pulses designed with quantum optimal control can manipulate molecular nanomagnet spin states more efficiently, enabling faster operations that mitigate decoherence in quantum systems.

Contribution

It introduces a method to optimize microwave pulses for controlling molecular spin qudits, enhancing operation speed and practical implementation potential.

Findings

Optimal control pulses perform state-to-state and gate transformations faster than monochromatic pulses.

Simulations show feasible implementation for a Gd$^{3+}$ ion with 8 levels, encoding an 8-level qudit.

Universal quantum gates can be achieved using intrinsic couplings and optimized pulses.

Abstract

We demonstrate, numerically, the possibility of manipulating the spin states of molecular nanomagnets with shaped microwave pulses designed with quantum optimal control theory techniques. The state-to-state or full gate transformations can be performed in this way in shorter times than using simple monochromatic resonant pulses. This enhancement in the operation rates can therefore mitigate the effect of decoherence. The optimization protocols and their potential for practical implementations are illustrated by simulations performed for a simple molecular cluster hosting a single Gd$^{3+}$ ion. Its eight accessible levels (corresponding to a total spin $S=7/2$) allow encoding an $8$-level qudit or a system of three coupled qubits. All necessary gates required for universal operation can be obtained with optimal pulses using the intrinsic couplings present in this system. The application of optimal control techniques can facilitate the implementation of quantum technologies based on molecular spin qudits.