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In order to demonstrate an applicability of quantum computing to fundamental electronic structure problems of molecules, we describe the Hückel Hamiltonian matrix in terms of quantum gates and obtain the orbital energies of fundamental π-electron molecules (C2H4, C3H4, C4H4, C4H6, and C6H6) using a superconducting-qubit-type quantum computer ( ibm_kawasaki) with a post-selection error mitigation method. We show that the orbital energies are obtained with sufficiently high accuracy and small uncertainties and that characteristic features of the electronic structure of the π-electron molecules can be extracted by quantum computing in a straightforward manner.

Significance The destruction of specimen molecules by an electron beam (e-beam) is either beneficial, as in mass spectrometry capitalizing on ion formation, or deleterious, as in electron microscopy. In the latter application, the e-beam not only produces the specimen image, but also causes information loss upon prolonged irradiation. However, the atomistic mechanism of such loss has been unclear. Performing single-molecule kinetic analysis of C 60 dimerization in a carbon nanotube (CNT) under variable-temperature/voltage conditions, we identified three reactive species—that is, radical cation, singlet, and triplet excited states—reacting competitively as the voltage and the properties of the CNT were changed. The key enabler was in situ continuous recording of the whole reaction process, suggesting an upcoming new era of “cinematic chemistry.”

Soot, which is produced through the rapid growth of hydrocarbon molecules in fuel-rich flames, has been proved to be responsible for global warming and harmful to the respiratory system of human. However, the complex formation process of soot in flames has not been understood yet because of the lack of efficient time-resolved methods for monitoring soot and its precursor species. We present here a viable pump–probe approach to measure ultrafast processes of the soot particles in flames with femtosecond time resolution. The scattering of femtosecond ultraviolet (UV) light pulses is used to monitor soot particles along alkanol–air diffusion flames from the inception phase up to the burnout region after the formation of a femtosecond laser filament in the flames. The time evolution of the scattered UV signal reveals unexpected ultrafast swelling and shrinking of soot particles induced by the femtosecond laser filament in the different flame regions. Our in situ and time-domain measurements of soot particles with the femtosecond time resolution unveil their unique properties in the flames.

We examine the dependences of the single and double ionization probabilities of NO radical on the angle between the NO axis and the laser polarization direction in an intense laser field (790 nm, 100 fs, 1–10 × 1014 W/cm2) and show that the double ionization is enhanced when the NO axis is parallel to the laser polarization direction. We reveal that the angular dependence of the sequential double ionization probability is determined by the shape of the 5σ orbital of NO+ from which the second photoelectron is emitted in the ionization from NO+ to NO2+. We also reveal that the fast oscillation in the probability of the tunnel ionization of NO originating from a coherent superposition of the two spin–orbit components in the electronic ground X2Π state is described well based on the molecular Ammosov-Delone-Krainov (MO-ADK) theory in which the time evolution of the electron density distribution of the 2π orbital is taken into account.

We study static-field ionization of He-like ions with nuclear charge number in the range of $2\le Z \le 36$. Both the tunneling and over-the-barrier regimes are considered. We calculate the ionization rates by three approximate methods: a fitting formula based on the Perelemov-Popov-Terent'ev (PPT) formula, a perturbative expansion in powers of $1/Z$, and a single-active electron approximation, and compare them with reference ionization rates computed by the multiconfiguration time-dependent Hartree-Fock (MCTDHF) approach. The relative deviation of the rates computed by the PPT-based fitting formula and the third-order perturbation theory from the rates computed by the MCTDHF approach is found to be around 10\%. We discuss quantitatively the contribution from the exchange interaction during the ionization by comparing the single-active electron rates and the reference rates in which multielectron effects are included. We find that a single-active electron approximation, where the exchange interaction is neglected, results in the overestimation of the ionization rates by 30\% for He and 2\% for He-like Kr, showing that the magnitude of the effect of the exchange interaction scales approximately as $1/Z$., 33 pages, 6 figures

We investigate the carrier-envelope phase dependences of the dissociative ionization processes of acetonitrile induced by intense near-IR few-cycle laser pulses based on the asymmetry in the emission direction of fragment ions.

We simulate the time-dependent dynamics of a three-site spin chain described by the Heisenberg XXX Hamiltonian. The quantum circuit representing the time-dependent wave function is constructed using the Suzuki-Trotter approximation, and is executed on the quantum computer ibm_kawasaki. At each time step, the density matrix of the three-qubit state is reconstructed by state tomography. By applying four different mitigation methods, Clifford data regression, Pauli twirling, density matrix purification, and density matrix orthogonalization, we demonstrate that accurate time-dependent populations and density matrices can be calculated on noisy superconducting-qubit type quantum computers.

Using a newly developed submicron focusing system equipped with a large-aperture Wolter mirror with a precisely figured surface, we irradiate a Ni thin film coated on a silicon substrate with femtosecond extreme ultraviolet (EUV) laser pulses, generated as high-order harmonics of near-infrared femtosecond laser pulses. At the fluence of up to 100 mJ cm−2 at the sample surface, we show that the surface morphology can be modified with a submicron spatial resolution and that a protruding structure is formed when the fluence is 60–70 mJ cm−2, exhibiting a characteristic feature of the femtosecond EUV light processing of a thin metal surface.

By adopting the variational quantum simulator method on noisy quantum computers, we simulate the temporal evolution of the population transfer in a laser-driven three-level system, representing [Formula: see text] suddenly exposed to an intense laser field. We have conducted experiments using an IBM Quantum computer. In order to mitigate the error caused by the execution of the Hadamard test circuits, the Clifford data regression method is adopted. The characteristic features in the temporal evolution of the population transfer, leading to the population inversion and the air lasing, have been well reproduced.

We investigate lasing of a nitrogen gas induced by intense femtosecond laser pulses at around 400 nm. By examining both the self-induced and externally seeded forward emission spectra, we unambiguously identify the ${{\mathrm{N}}_{2}}^{+}$ lasing actions at 427.8 and 423.6 nm assigned respectively to the $B\phantom{\rule{0.16em}{0ex}}{}^{2}\mathrm{\ensuremath{\Sigma}}{{}_{u}}^{+}\ensuremath{-}X^{2}\mathrm{\ensuremath{\Sigma}}_{g}^{\phantom{\rule{0.28em}{0ex}}+}$ (0, 1) and (1, 2) emissions and show that the lasing mechanism is totally different from the lasing induced by near-infrared (800 nm) laser pulses, in which the population transfer from $X^{2}\mathrm{\ensuremath{\Sigma}}_{g}^{\phantom{\rule{0.28em}{0ex}}+}$ to $A^{2}\mathrm{\ensuremath{\Pi}}_{u}$ proceeds through the resonant $X^{2}\mathrm{\ensuremath{\Sigma}}_{g}^{\phantom{\rule{0.28em}{0ex}}+}\ensuremath{-}A^{2}\mathrm{\ensuremath{\Pi}}_{u}$ transition, facilitating the population inversion between the $B\phantom{\rule{0.16em}{0ex}}{}^{2}\mathrm{\ensuremath{\Sigma}}{{}_{u}}^{+}\ensuremath{-}X^{2}\mathrm{\ensuremath{\Sigma}}_{g}^{\phantom{\rule{0.28em}{0ex}}+}$ states [Phys. Rev. Lett. 123, 203201 (2019)]. We simulate the population distributions among the vibrational levels in the three lowest electronic states of ${{\mathrm{N}}_{2}}^{+}$ by the 400-nm laser pumping and find that the population is efficiently transferred between the $X^{2}\mathrm{\ensuremath{\Sigma}}_{g}^{\phantom{\rule{0.28em}{0ex}}+}$ state and the $B\phantom{\rule{0.16em}{0ex}}{}^{2}\mathrm{\ensuremath{\Sigma}}{{}_{u}}^{+}$ state by a Rabi oscillation combined with a Raman-type transition, leading to the population inversion so that the lasing occurs at the $B\phantom{\rule{0.16em}{0ex}}{}^{2}\mathrm{\ensuremath{\Sigma}}{{}_{u}}^{+}\ensuremath{-}X^{2}\mathrm{\ensuremath{\Sigma}}_{g}^{\phantom{\rule{0.28em}{0ex}}+}$ (0, 1) and (1, 2) emissions.

The authors determine the spin-orbit-splitting energies in the electronic ground states of Ar${}^{+}$, Kr${}^{+}$, and Kr${}^{2+}$ from the temporal evolution of wave packets generated by strong-field ionization of the neutral atoms and the singly charged ion, respectively. The results are in agreement with earlier measurements with significantly improved precision.

The lasing of ${\mathrm{N}}_{2}{}^{+}$ at 391 nm, originating from the population inversion between $X{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}_{g}{}^{+}(v=0)$ and $B{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}_{u}{}^{+}(v=0)$ achieved by the irradiation of a pair of few-cycle intense near-IR laser pulses in a pump-probe scheme, is investigated both experimentally and theoretically. The characteristic periodic intensity modulations recorded experimentally in both $P$- and $R$-branch emission lines are reproduced well by the theoretical simulation, in which the population transfer processes among the rovibrational levels of the three lowest electronic states, $X{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}_{g}{}^{+}, A{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Pi}}}_{u}$, and $B{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}_{u}{}^{+}$, of ${\mathrm{N}}_{2}{}^{+}$ induced by pump and probe few-cycle intense laser pulses are calculated. Based on the results of the theoretical simulation, the periodic intensity modulations are ascribed to the difference between the rotational selection rules in the $A{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Pi}}}_{u}\ensuremath{-}X{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}_{g}{}^{+}$ coupling, which suppresses the rotational excitation in the $X{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}_{g}{}^{+}(0)\phantom{\rule{0.28em}{0ex}}\text{state}$, and those in the $B{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}_{u}{}^{+}\ensuremath{-}X{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}_{g}{}^{+}$ coupling, which enhances the rotational excitation in the $B{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}_{u}{}^{+}$(0) state.

Cavity-free air lasing offers a promising route towards the realization of atmospheric lasers for various applications such as remote sensing and standoff spectroscopy; however, achieving efficient generation and control of air lasing in ambient air is still a challenge. Here we show the experimental realization of a giant lasing enhancement by three to four orders of magnitude in ambient air for the self-seeded

Photodissociation of [Ar-N

Pump-probe measurements of methanol and its isotopologues (CH3OH, CH3OD and CD3OH) were performed using near-infrared few-cycle intense laser pulses. The yields of the parent ion and the fragment i...

In order to develop a method for evaluating vibrational energies and wave functions of a polyatomic molecule by quantum computing, we introduce the reduced multistate contracted variational quantum eigensolver (RMC-VQE) method, which is a variant of the multistate contracted VQE method [Parrish et al., Phys. Rev. Lett. 122, 230401 (2019)], and apply the RMC-VQE method to a two-mode model of CO2. In the RMC-VQE method, much fewer matrix elements of the Hamiltonian are evaluated on the quantum computer than in the MC-VQE method. By measuring the matrix elements of the Hamiltonian using the quantum computer ibm_kawasaki and diagonalizing the Hamiltonian matrix on a classical computer, we obtain the vibrational energies of the Fermi doublet, which differ from the exact energies obtained using a classical computer by less than 0.1 cm−1. We also obtain accurate vibrational wave functions of the Fermi doublet states.

We apply a modified version of the multistate contracted variational quantum eigensolver method to calculate vibrational eigenstates of ${\mathrm{CO}}_{2}$ on a quantum computer. A two-mode model of ${\mathrm{CO}}_{2}$ is employed, and the vibrational wave function is expanded using three harmonic-oscillator basis functions for each mode. The wave functions are mapped to four qubits by a compact mapping method. The Hamiltonian matrix elements are evaluated on a simulator including noise and on a quantum computer available at IBM Quantum, while the Hamiltonian matrix is diagonalized on a classical computer. We propose an error mitigation method by which the shift of the numerical values of the matrix elements originating from the noise can be corrected, and examine the dependence of the statistical uncertainties on the number of executions of each quantum circuit. We find that, at about $8\ifmmode\times\else\texttimes\fi{}{10}^{6}$ executions, the energy eigenvalues of the Fermi resonance states in ${\mathrm{CO}}_{2}$ can be obtained with an uncertainty within 1 ${\mathrm{cm}}^{\ensuremath{-}1}$.

We investigate the carrier-envelope phase (CEP) dependences of the single and double ionization processes of methanol (CH3OH) in an intense near-IR few-cycle laser field (2.1 × 1014 W/cm2) by the asymmetry in the ejection direction of CH3+ for the non-hydrogen migration channels and CH2+ for the hydrogen migration channels created through the C–O bond breaking after the ionization. Based on the absolute CEP values at the laser–molecule interaction point, calibrated by the method using intense few-cycle circularly polarized laser pulses [Fukahori et al., Phys. Rev. A 95, 053410-1–053410-14 (2017)], we confirm that methanol cations are produced by tunnel ionization and methanol dications are produced by the recollisional double ionization. We obtain the phase offset for the double ionization accompanying no hydrogen migration to be 1.85π as the absolute CEP at which the extent of the asymmetry becomes maximum. We interpret the phase shift of 0.85π from the phase offset of 1.0π for the tunnel ionization, estimated by a tunnel ionization model incorporating the chemical bond asymmetry, as the corresponding time delay associated with the electron recollisional ionization. The positive phase shift of 0.13π for the single ionization in the non-hydrogen migration channel is interpreted as the additional time (165 as) with which a methanol cation can be excited electronically prior to the decomposition. The additional phase shift of 0.22π for the single ionization in the hydrogen migration channel is interpreted as the additional time (280 as) required for a methanol cation to be excited electronically leading to the hydrogen migration prior to the decomposition.

Our recent studies on ultrafast nuclear dynamics and high-resolution spectroscopy of isolated molecular ions in which intense few-cycle near-IR laser pulses are used are introduced. By the pump–probe measurements of the fragmentation processes of methanol cations, we investigate ultrafast hydrogen migration in methanol cation in the time domain and determine vibrational frequencies of methanol cations in the frequency domain by Fourier transform of the yields of parent and fragment ions. We further demonstrate that the rovibrational level energy separations of D2 and D 2 + can be determined with ultrahigh resolution by strong-field Fourier transform spectroscopy.

THz-wave assisted electron scattering by Ar, in which the scattered electrons exchange their energy with as many as 800 photons, was observed unambiguously as a first step for ultrafast electron diffraction by the THz-wave streaking.

We investigate the photoionization of ${\mathrm{H}}_{2}$ by an attosecond pulse train using reduced density matrices and reveal that the phase of the photoelectron introduces a time delay in the coherent vibrational motion of ${\mathrm{H}}_{2}^{+}$. We show that, even when the ionization laser pulse is Fourier limited, the reduced density matrix of ${\mathrm{H}}_{2}^{+}$ contains an intrinsic phase ascribed to the phase of the photoelectron wave function and that the intrinsic phase can be extracted by pump-probe measurements as long as the pump-probe time delay is measured with precision of the order of tens of attoseconds.

Porphyrin-fullerene dyads were intensively studied as molecular donor-acceptor systems providing efficient photoinduced charge separation (CS). A practical advantage of the dyads is the possibility to tune its CS process by the porphyrin periphery modification, which allows one to optimize the dyad for particular applications. However, this tuning process is typically composed of a series of trial stages involving the development of complex synthetic schemes. To address the issue, we synthesized a series of dyads with properties switching between electron and energy transfer in both polar (benzonitrile) and nonpolar (toluene) media and developed a computation procedure with sufficient reliability by which we can predict the CS properties of the dyad in different media and design new dyads. The dyads photochemistry was established by conducting ultrafast transient absorption studies in toluene, anisole, and benzonitrile. The most crucial step in computational modeling was to establish a procedure for correction of the electronic-state energies obtained by DFT so that the effects of the electron correlation and the long-range interactions are properly incorporated. We also carried out standard electrochemical measurements and show that our computation approach predicts better thermodynamics of the dyads in different solvents.

We establish a generalized picture of the phase sensitivity of laser-induced directional bond breaking using the H_{2} molecule as the example. We show that the well-known proton ejection anisotropy measured with few-cycle pulses as a function of their carrier-envelope phases arises as an amplitude modulation of an intrinsic anisotropy that is sensitive to the laser phase at the ionization time and determined by the molecule's electronic structure. Our work furthermore reveals a strong electron-proton correlation that may open up a new approach to experimentally accessing the laser-sub-cycle intramolecular electron dynamics also in larger molecules.

The authors generate air lasing by elliptically-modulated intense femtosecond laser pulses and show that the lasing intensities of N${}_{2}$${}^{+}$ at 391 and 428 nm can be manipulated by adjusting the temporal separation between the two polarization components in the elliptically-modulated laser pulse and their relative amplitudes. The authors interpret this characteristic ellipticity dependence in terms of the post-ionization coupling occurring in the later part of the laser pulse, which depletes efficiently the population in the X${}_{2}$ ${\mathrm{\ensuremath{\Sigma}}}_{g}^{+}$ (v'' = 0) state.

The alignment-dependent sequential-double-ionization probability of NO in intense laser fields is determined by the shape of the 5σ orbital, from which the second photoelectron is ejected associated with the saturation of the first ionization.

When intense femtosecond laser pulses are focused in air, unidirectional and coherent radiation called air-lasing is generated, originating from the population inversion processes between an electronically excited state and the electronic ground state of N\(_2\) and N\(_2{^{+}}\). In 2015, it was shown experimentally that the air-lasing at 391 nm, corresponding to the \(\mathrm{B}{}^2\Sigma _\mathrm{u}{^+}(v = 0)-\mathrm{X}{}^2\Sigma _\mathrm{g}{^+}(v = 0)\) emission of N\(_2{^{+}}\), is generated in an sub-10 fs near-IR laser field (Xu et al, Nat Commun 6:8347, 2015 [6]). The behavior that N\(_2{^{+}}\) generated in the pulse is exposed to the intense laser field immediately after its birth, is considered critical in leading to the population inversion between the B and X states. This chapter includes the demonstrations that the sudden exposure to an intense laser field could result in efficient population transition in a two-level system at off-resonance (Zhang et al, J Phys B: At Mol Opt Phys 50:185603, 2017 [32]), and that population inversion can be achieved in N\(_2{^{+}}\) by using sudden turn-on pulse (Zhang et al, J Phys B: At Mol Opt Phys 52:055401, 2019 [33]). This scenario of the population transfer to the excited state is expected to be universal and can be applied to an interpretation of population inversion of any kind of atomic and molecular ions created in a pulsed intense laser field.

We show using reduced density matrices that a phase of the photoelectron created in the photoionization of H2 induced by an attosecond pulse train introduces time delay in the coherent vibrational motion of H 2 + .

We investigate the rotational population inversion between the electronically excited B state and the ground X state in N2+ generated in an intense laser field by including electronic, vibrational and rotational degrees of freedom.