Composite pulses for population transfer in the interaction of two-level nuclear systems with X-ray laser pulses

Population transfer of two-state nuclei interacting with a train of composite X-ray free electron laser (XFEL) pulses has been investigated theoretically. In this study, we calculate the effective intensity of the XFEL pulse for each nucleus so that the time temporal pulse area of Rabi frequency is equal to $$\pi$$. We show that with increasing the number of composite pulses, even with a significant deviation of the effective intensity of the laser beam from the calculated value, the population is completely transferred from the ground state to the excited state. For numerical study, nuclei with a high lifetime in the excited state, compared to the XFEL laser pulse duration, have been selected so that the effect of spontaneus emission can be neglected. Finally, it has been shown that despite the detuning effects, by increasing the number of XFEL composite pulses as well as the effective intensity of the laser pulse, the population is completely transferred to the excited state

Synthesis of fast qudit gates by a train of coincident pulses

We propose an exact analytical method for the production of fast quantum gates in a system of d degenerate states, using a technique of a train of coincident pulses. It is an alternative to the adiabatic passage technique. This study exploits the Morris-Shore transformation and generalized quantum Householder reflection in which each of Householder reflection is implemented by n + m (n and m are arbitrary integers) sets of coincident pulses. Decoherence due to the population of the upper state is efficiently suppressed as the number of pulse sets (n and m) increases. It is remarkable that the upper state population is damped considerably, even for a small number of pulse sets, despite the fact that all the fields applied were on resonance with their transitions. In this method, simple Gaussian pulses with minimal pulse areas were used, which is easy to achieve experimentally. As a case study to validate the method, we implement the quantum Fourier transform in qutrit and ququad by a proper pulse train