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arXiv:2311.15686 · The Journal of Chemical Physics

Quantum state engineering in a five-state chainwise system by generalized coincident pulse technique

Jiahui Zhang

Published Aug 15, 2024• 1 citation
arXivHTMLPDF

Abstract

In this paper, an exact analytical solution is presented for achieving coherent population transfer and creating arbitrary coherent superposition states in a five-state chainwise system by a train of coincident pulses. We show that the solution of a five-state chainwise system can be reduced to an equivalent three-state Λ-type one with the simplest resonant coupling under the assumption of adiabatic elimination together with a requirement of the relation among the four coincident pulses. In this method, the four coincident pulses at each step all have the same time dependence, but with specific magnitudes. The results show that, by using a train of appropriately coincident pulses, this technique not only enables complete population transfer, but also creates any desired coherent superposition between the initial and final states, while the population in all intermediate states is effectively suppressed. Furthermore, this technique can also exhibit a one-way population transfer behavior. The results are of potential interest in applications where high-fidelity multi-state quantum control is essential, e.g., quantum information, atom optics, formation of ultracold molecules, cavity QED, nuclear coherent population transfer, and light transfer in waveguide arrays.

DOI
10.1063/5.0223526

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This paper presents an exact analytic solution for creation of any preselected coherent superposition of states in multi-lambda quantum systems by a train of coincident pulses. We show that the solution of a multi-lambda system composed of degenerate ground states, excited states, and a single initial state can be reduced by using Morris–Shore transformation to the solution of a three-state system. In this method, all of the pump and Stokes pulses have the same time dependence and the ratio of the pump pulses can be used to control the probability amplitudes of the ground states in the coherent superposition of states. Effect of spontaneous emission is efficiently suppressed by employing a train of coincident pulses. This technique resembles the technique of generalized -pulses with minimal pulse areas which is easy to reach experimentally.
We propose a scheme for coherent control of population transfer and arbitrary superpositions of quantum states by a single-chirped laser pulse in a Λ-type excited-doublet four-level system. It is shown that selective, efficient, and robust population transfer from the initial state to the target states (excited or ground) can be achieved via chirped adiabatic passage when the pulse bandwidth is smaller than about 1/10 of the energy separations between the excited-doublet levels and between the ground states. Moreover, arbitrary coherent superpositions between the excited-doublet states, or between the higher ground state and either of the excited-doublet states, can be created by appropriately tuning the chirp rate and detuning the laser field. The proposed flexible method of coherent control of population transfer and arbitrary superpositions between the initially unpopulated states requires only a single pulse, and is robust against variations in the laser parameters, which has potential applications in quantum information processing.
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