2021 Fiscal Year Annual Research Report
Theoretical studies on photo-excitation processes of molecular ions generated in intense laser fields
| Project/Area Number |
20J23551
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| Research Institution | The University of Tokyo |
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Principal Investigator |
ZHANG Youyuan 東京大学, 理学系研究科, 特別研究員(DC1)
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| Project Period (FY) |
2020-04-24 – 2023-03-31
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| Keywords | Rotational excitation / Population transfer / Dynamics / Quantum simulation / Intense laser field |
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| Outline of Annual Research Achievements |
In this academic year, I have worked on the classical and quantum simulation of time-dependent population transfer induced by the post-ionization excitation. I have focused on a phenomenon called air lasing, in which coherent and unidirectional radiation at 391 nm is generated when nitrogen molecular ions are formed by the irradiation of intense femtosecond laser pulses. I have developed a complete theoretical model including the electronic, vibrational, and rotational excitations to simulate the population inversion process in N_2^+ in the air lasing.
The achievements can be summarized as below:
1. The origin of the rotational coherence in the air lasing by reproducing not only the major features but also the unique appearance of the two R branch profiles. This work was published in Physical Review A 104, 023107 (2021) with the title of “Rotational population transfer through the A^2Π_u^+ - X^2Σ_g^+- B^2Σ_u^+ coupling in N_2^+ lasing”.
2. To include the ionization effect in the simulation, I have examined the dependence of the population transfer process in N_2^+ on the ionization timing within an intense laser pulse.
3. To take advantage of quantum computer, I have started implementing the complete theoretical model for post-ionization excitation simulation to quantum algorithm. By adopting the variational quantum eigensolver method, I have developed a quantum algorithm for the simplest three-level system representing the post-ionization processes of N_2^+ based on the sudden turn-on model.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
I have focused on the simulation of time-dependent population transfer induced by strong field ionization. I first developed a complete theoretical model including the electronic, vibrational, and rotational excitations to simulate the post-ionization excitation, which has been used to understand the population inversion mechanism of air-lasing at 391 nm. In this physical year, this model has been successfully applied to explain the origin of the rotational coherence among the X, A, and B states in N_2^+ induced by intense pump and probe laser pulses and understand the unique appearance of the two R branch profiles in the emission spectrum.
As the ionization can occur at different time in a laser pulse with the ionization probability depending on the ionization timings. I have examined the dependence of the population transfer in N_2^+ on the ionization timing within an intense laser pulse. By integrating the post-ionization excitation process at different ionization timings, I have interpreted the population transfer dynamics during the entire laser pulse duration.
In the past few years, with the advent of quantum computers, researchers have been investigating intensively how a stationary Schrodinger equation can be solved on a quantum computer. However, algorithms for simulating dynamical processes of atoms and molecules interacting with an intense light field have not been developed well. By adopting the variational quantum eigensolver method, I have developed a quantum algorithm for computing of the post-ionization processes of N_2^+ based on the sudden turn-on model.
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| Strategy for Future Research Activity |
Based on the results of the simulations performed in the past academic year, I will further investigate the problem of the ionization timing, so that all the ionization processes induced throughout the entire laser pulse can be thoroughly understood.
Secondly, we plan to develop a quantum algorithm for simulating the post-ionization excitation process with multi-level systems using the sudden turn-on model on a quantum computer.
Thirdly, by taking advantage of the theoretical methods I have developed in the past fiscal year on the ionization and excitation of molecular systems, I will investigate theoretically how molecules are ionized and excited by an attosecond laser pulse whose wavelength is in the extreme ultraviolet region.
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Research Products
(6 results)
