Superposition States in Cavities Fed by Injected Atoms

Quantum simulations of the electron dynamics of oriented benzene and Mg-porphyrin driven by short (<10 fs) laser pulses yield electron symmetry breaking during attosecond charge migration. Nuclear motions are negligible on this time domain, i.e., the point group symmetries G = D6h and D4h of the nuclear scaffolds are conserved. At the same time, the symmetries of the one-electron densities are broken, however, to specific subgroups of G for the excited superposition states. These subgroups depend on the polarization and on the electric fields of the laser pulses. They can be determined either by inspection of the symmetry elements of the one-electron density which represents charge migration after the laser pulse, or by a new and more efficient group-theoretical approach. The results agree perfectly with each other. They suggest laser control of symmetry breaking. The choice of the target subgroup is restricted, however, by a new theorem, i.e., it must contain the symmetry group of the time-dependent electronic Hamiltonian of the oriented molecule interacting with the laser pulse(s). This theorem can also be applied to confirm or to falsify complementary suggestions of electron symmetry breaking by laser pulses.

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Control of quantum electrodynamical processes by shaping electron wavepackets

Nature Communications ◽

10.1038/s41467-021-21367-1 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Liang Jie Wong ◽

Nicholas Rivera ◽

Chitraang Murdia ◽

Thomas Christensen ◽

John D. Joannopoulos ◽

...

Keyword(s):

Free Electron ◽

Spectral Characteristics ◽

Modern Science ◽

Optical Excitation ◽

Field Theories ◽

Photon Scattering ◽

Precise Control ◽

Bremsstrahlung Emission ◽

Superposition States ◽

Electron Photon

AbstractFundamental quantum electrodynamical (QED) processes, such as spontaneous emission and electron-photon scattering, encompass phenomena that underlie much of modern science and technology. Conventionally, calculations in QED and other field theories treat incoming particles as single-momentum states, omitting the possibility that coherent superposition states, i.e., shaped wavepackets, can alter fundamental scattering processes. Here, we show that free electron waveshaping can be used to design interferences between two or more pathways in a QED process, enabling precise control over the rate of that process. As an example, we show that free electron waveshaping modifies both spatial and spectral characteristics of bremsstrahlung emission, leading for instance to enhancements in directionality and monochromaticity. The ability to tailor general QED processes opens up additional avenues of control in phenomena ranging from optical excitation (e.g., plasmon and phonon emission) in electron microscopy to free electron lasing in the quantum regime.

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Coherent manipulation and quantum phase interference in a fullerene-based electron triplet molecular qutrit

npj Quantum Information ◽

10.1038/s41534-021-00362-w ◽

2021 ◽

Vol 7 (1) ◽

Author(s):

Ye-Xin Wang ◽

Zheng Liu ◽

Yu-Hui Fang ◽

Shen Zhou ◽

Shang-Da Jiang ◽

...

Keyword(s):

Quantum Information Processing ◽

Quantum Phase ◽

Information Storage ◽

Paramagnetic Resonance ◽

Molecular Electron ◽

Phase Interference ◽

Superposition States ◽

Pulsed Electron Paramagnetic Resonance ◽

Electron Paramagnetic ◽

Coherent Manipulation

AbstractHigh-spin magnetic molecules are promising candidates for quantum information processing because their intrinsic multiplicity facilitates information storage and computational operations. However, due to the absence of suitable sublevel splittings, their susceptibility to environmental disturbances and limitation from the selection rule, the arbitrary control of the quantum state of a molecular electron multiplet has not been realized. Here, we exploit the photoexcited triplet of C70 as a molecular electron spin qutrit with pulsed electron paramagnetic resonance. We prepared the system into 3-level superposition states characteristic of a qutrit and validated them by the tomography of their density matrices. To further elucidate the coherence of the operation and the nature of the system as a qutrit, we demonstrated the quantum phase interference in the superposition. The interference pattern is further interpreted as a map of possible evolution paths in the space of phase factors, representing the quantum nature of the 3-level system.

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