Not gate in a cis-trans photoisomerization model

TL;DR

This study demonstrates how laser pulses can implement a classical NOT gate in a molecular system by controlling cis-trans isomerization, achieving high fidelity and analyzing stability under environmental interactions.

Contribution

It introduces a method to realize a classical NOT gate in a molecular system using optimal control of laser pulses, with analysis of robustness against environmental effects.

Findings

High fidelity in laser-controlled cis-trans isomerization.

Control remains stable under Markovian bath conditions.

Applicable to retinal models in rhodopsin.

Abstract

We numerically study the implementation of a NOT gate by laser pulses in a model molecular system presenting two electronic surfaces coupled by non adiabatic interactions. The two states of the bit are the fundamental states of the cis-trans isomers of the molecule. The gate is classical in the sense that it involves a one-qubit flip so that the encoding of the outputs is based on population analysis which does not take the phases into account. This gate can also be viewed as a double photo-switch process with the property that the same electric field controls the two isomerizations. As an example, we consider one-dimensional cuts in a model of the retinal in rhodopsin already proposed in the literature. The laser pulses are computed by the Multi Target Optimal Control Theory with chirped pulses as trial fields. Very high fidelities are obtained. We also examine the stability of the control when the system is coupled to a bath of oscillators modelled by an Ohmic spectral density. The bath correlation time scale being smaller than the pulse duration the dynamics is carried out in the Markovian approximation.