Double-slit photoelectron interference in strong-field ionization of the neon dimer (1803.07355v1)

Abstract: Wave-particle duality is an inherent peculiarity of the quantum world. The double-slit experiment has been frequently used for understanding different aspects of this fundamental concept. The occurrence of interference rests on the lack of which-way information and on the absence of decoherence mechanisms, which could scramble the wave fronts. In this letter, we report on the observation of two-center interference in the molecular frame photoelectron momentum distribution upon ionization of the neon dimer by a strong laser field. Postselection of ions, which were measured in coincidence with electrons, allowed choosing the symmetry of the continuum electronic wave function, leading to observation of both, gerade and ungerade, types of interference.

• The paper demonstrates that strong-field ionization in neon dimers produces double-slit interference patterns with distinct kinetic energy releases.
• Researchers employed ultrafast (40 fs, 780 nm) laser pulses and COLTRIMS spectroscopy to resolve electron momentum and differentiate orbital symmetries.
• The study confirms theoretical models by matching interference fringes with phase differences between gerade and ungerade electronic states.

Analysis of Double-slit Photoelectron Interference in Strong-field Ionization of the Neon Dimer

The paper by Kunitski et al. presents an empirical investigation of quantum mechanical phenomena, specifically examining double-slit interference within the context of strong-field ionization of the neon dimer. The paper primarily focuses on observing two-center interference in the momentum distribution of photoelectrons post-ionization. By utilizing a strong laser field, the research emphasizes intricacies within the molecular frame that enable the observation of interference patterns analogous to the archetypal double-slit experiments.

Key Observations and Methodology

The researchers demonstrated that strong-field ionization can manifest interference patterns that have conventionally been associated with simpler photonic experiments. The methodology employed involved the ionization of neon dimers using an intense ultrafast laser (780 nm, 40 fs), with charged products post-ionization detected through COLTRIMS spectroscopy. This enabled precise measurement of electron momentum components aligned with the molecular axis.

Their experiments were uniquely structured to discern ionization events that distinguish between the gerade and ungerade electronic states. By postselecting ions measured in coincidence with electrons, the researchers successfully isolated and investigated interference patterns for different molecular electron orbitals, essentially switching between interference behaviors.

Results and Numerical Observations

An essential outcome was the observation of distinct kinetic energy releases (KER) that correlated with interference patterns in the dimer photoionization process. The paper reported two energy structures at approximately 0.25 eV and 1.3 eV, which were linked to the distinct ionization pathways of the 2pσ orbitals. The ability to detect interference patterns aligned with the theoretical equation $P \sim \cos^2 ((k \cdot R/2) + \Delta\phi/2)$ confirmed the experimental viability of the two-center interference concept within a molecular framework.

The interference pattern depended significantly on the symmetry of the originating molecular orbitals and the associated difference in phase $\Delta\phi$, with notable impacts on electron momentum distributions under both circular and linear laser polarizations. Specifically, the observation of interference with a minimum at zero momentum aligned with a scenario where $\Delta\phi = \pi$.

Theoretical Implications and Predictions

Theoretically, the results support the notion that the principles governing double-slit interference extend to ions and challenging ultrafast processes. The paper emphasizes how manipulation of molecular configurations can provide insights into quantum mechanics fundamentals and electron dynamics. Additionally, the researchers use the interference pattern to measure bond distances, thereby enhancing diffractive imaging's scope.

Furthermore, the research underlines the interaction of liberated electrons with neighboring atomic structures within the dimer as a factor affecting interference pattern contrasts, contributing to a better understanding of quantum decoherence, localization, and interaction effects.

Conclusion and Future Directions

The work by Kunitski et al. enriches the comprehension of two-center interference phenomena within the strong-field ionization regime. It bridges a conceptual gap between classical optical experiments and complex molecular interactions in ultrafast conditions. The confirmation of interference patterns aligned with strong-field ionization proposes extensions into time-resolved quantum probing techniques that could offer profound insights into molecular dynamics, quantum coherence, and particle-wave duality.

Future endeavors should focus on characterizing these phenomena across a broader spectrum of molecular systems and exploring the potential for real-time measurement of quantum mechanical processes. Such work could catalyze advancements in quantum imaging techniques and deepen understanding of the quantum wave function in various complex systems.