Optimal molecular alignment and orientation through rotational ladder climbing

Abstract

We study the control by electromagnetic fields of molecular alignment and orientation, in a linear, rigid rotor model. With the help of a monotonically convergent algorithm, we find that the optimal field is in the microwave part of the spectrum and acts by resonantly exciting the rotation of the molecule progressively from the ground state, i.e., by rotational ladder climbing. This mechanism is present not only when maximizing orientation or alignment, but also when using prescribed target states that simultaneously optimize the efficiency of orientation/alignment and its duration. The extension of the optimization method to consider a finite rotational temperature is also presented.

Fully efficient time-parallelized quantum optimal control algorithm

“…Given a target value ε of the figure of merit, we measure the computational time necessary to obtain it. In the numerical computation, we use ε = 0.3, while the optimum has been numerically estimated as 0.2909 [42]. The values of the figure of merit are plotted in Fig.…”

“…Molecular orientation [33,34] is nowadays a wellestablished topic both from the experimental [35,36] and theoretical points of views [37][38][39][40][41]. Different optimal control analyses have been made on this quantum system [42][43][44][45].…”

“…We refer the reader to Ref. [42] for details on the numerical implementation of this control problem. The α parameter is chosen as a time-dependent function of the form 10 5 ( t − T /2 T /2 ) 6 + 10 4 in order to design a control field which is experimentally relevant [42].…”

“…[42] for details on the numerical implementation of this control problem. The α parameter is chosen as a time-dependent function of the form 10 5 ( t − T /2 T /2 ) 6 + 10 4 in order to design a control field which is experimentally relevant [42]. The target state is the eigenvector of the observable cos θ with the maximum eigenvalue in the subspace such that j ≤ 4 [39,46].…”

Exploring quantum control landscapes: Topology, features, and optimization scaling

“…OCT simulations have successfully controlled a variety of objectives, including state preparation [2,6,7], molecular isomerization [8][9][10][11][12], dissociation [13][14][15][16], and orientation/alignment [17][18][19]. OCE using ultrafast tailored laser pulses have achieved control over many processes including state preparation [20,21], selective molecular dissociation [22][23][24], generation of high order optical harmonics [25][26][27], and energy transfer and isomerization in large biomolecules [28][29][30].…”