Real-time single-molecule imaging of quantum interference (1402.1867v1)

Abstract: The observation of interference patterns in double-slit experiments with massive particles is generally regarded as the ultimate demonstration of the quantum nature of these objects. Such matter-wave interference has been observed for electrons, neutrons, atoms and molecules and it differs from classical wave-physics in that it can even be observed when single particles arrive at the detector one by one. The build-up of such patterns in experiments with electrons has been described as the "most beautiful experiment in physics". Here we show how a combination of nanofabrication and nanoimaging methods allows us to record the full two-dimensional build-up of quantum diffraction patterns in real-time for phthalocyanine molecules PcH2 and their tailored derivatives F24PcH2 with a mass of 1298 amu. A laser-controlled micro-evaporation source was used to produce a beam of molecules with the required intensity and coherence and the gratings were machined in 10 nm thick silicon nitride membranes to reduce the effect of van der Waals forces. Wide-field fluorescence microscopy was used to detect the position of each molecule with an accuracy of 10 nm and to reveal the build-up of a deterministic ensemble interference pattern from stochastically arriving and internally hot single molecules.

Real-time Single-molecule Imaging of Quantum Interference

The paper "Real-time Single-molecule Imaging of Quantum Interference" by Thomas Juffmann et al. presents a significant advancement in the experimental demonstration of quantum wave-particle duality through the real-time imaging of interference patterns in phthalocyanine molecules. This paper leverages a sophisticated combination of nanofabrication, nanoimaging, and fluorescence microscopy techniques to visualize the quantum interference of large molecules, which were previously challenging to observe in a controlled, real-time manner.

Central to the experiment is the use of a laser-controlled micro-evaporation source for generating a coherent molecular beam and a nanomachined silicon nitride diffraction grating, which is crucial for minimizing the disruptive van der Waals interactions during interference. The molecules chosen for this paper, phthalocyanines (PcH2) and their fluoroalkylated derivatives (F24PcH2), serve as excellent candidates due to their stability in vacuum and their efficiency as fluorescent dyes.

The researchers have adeptly managed to achieve single-molecule diffraction, presenting a clear demonstration of wave-particle duality and enhancing the understanding of quantum mechanics principles. The advancement lies in the paper's ability to not only detect but visually monitor the stochastic build-up of interference patterns in real-time from single molecules. This achievement is facilitated by wide-field fluorescence microscopy, which offers a detection accuracy of up to 10 nm, emphasizing a substantial leap from existing methodologies such as scanning tunneling microscopy or electron-impact quadrupole mass spectrometry.

One of the principal breakthroughs of this research is the optical visualization of the temporal development of a 2D quantum interferogram from single molecules arriving stochastically. The ability to observe interference buildup provides a deeper insight into the quantum interference phenomena, supporting theoretical propositions and providing a basis for future studies on molecular interference and decoherence.

Strong numerical results were observed, notably the detection efficiency surpassing previous techniques by more than a factor of 10. This has enabled the paper of larger molecular complexes, thereby pushing the limits of diffraction experiments. It was also shown that reducing the grating thickness to a nanoscale dimension markedly mitigates undesired interactions, such as the van der Waals forces, which could influence the diffraction outcomes.

The theoretical ramifications of this paper extend beyond mere visualization. The findings enhance our empirical understanding of quantum mechanics, specifically the interactions at the molecular level and the transition from quantum to classical systems. This experimental setup, with its enhanced precision and sensitivity, is relevant for studies on quantum coherence, decoherence, and the scalability of quantum effects in complex systems. Analyzing the van der Waals interactions numerically provides opportunities for further investigation into molecular interactions at quantum scales.

Practically, the methods introduced in this research have significant implications for the development of techniques in quantum technology, such as in quantum computing and materials science, where understanding molecular interactions at quantum levels is critical. The high sensitivity and scalability of fluorescence imaging can be applied to various organic molecules and quantum dots, opening avenues for advanced material design and analysis.

Future work will likely involve refining the experimental techniques to increase precision, such as through enhanced velocity selection or improved grating designs, which could further reduce molecule-wall interactions. The paper suggests future explorations of double-layer graphene as alternative diffraction materials or leveraging light gratings could mitigate these interactions significantly.

In conclusion, this research contributes a valuable platform for ongoing exploration of quantum phenomena at the molecular scale, supporting both theoretical investigations and practical applications in quantum sciences.