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Molecular imaging
Advanced microscopy

Here’re some articles on advanced microscopy research, including quantum microscopy by coincidence.

Not included (as yet) below is an article about nano fab of crystal lattices – direct deposition of individual atoms at lattice sites vs. more conventional doping (impurity) techniques.

1 . Studying ultrafast molecular dynamics

  • Observing molecular processes that occur on timescales faster than a millionth of a billionth of a second
  • Imaging changes in bond lengths and angles between individual atoms while electrons shift position
  • Collecting spectral signals at the femtosecond timescale

• > “Ultrafast X-ray spectroscopy: Watching molecules relax in real time” by Rachel Berkowitz, Lawrence Berkeley National Laboratory (May 24, 2023) – Examining how a molecule responds to light on extremely fast timescales allows researchers to track how electrons move during a chemical reaction.

(image caption)
D-scan measurement. The pulse reconstructed in (D) from the measurement shown in (A) has a pulse duration of 5 fs and relative peak-power of 76% which proves the good degree of compression. (B) shows the D-scan retrieved by the software (Sphere Ultrafast Photonics). (C) shows the spectrum (red) and its spectral phase (blue). Credit: Science (2023). DOI: 10.1126/science.adg4421

(video visualization caption)
The angles between atoms in an excited methane molecule change as the molecule relaxes, distorting its shape and redistributing the absorbed energy. Credit: Diptarka Hait/Berkeley Lab

Designing the next generation of efficient energy conversion devices for powering our electronics and heating our homes requires a detailed understanding of how molecules move and vibrate while undergoing light-induced chemical reactions.

Researchers at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have now visualized the distortions of chemical bonds in a methane molecule after it absorbs light, loses an electron, and then relaxes. Their study provides insights into how molecules react to light, which can ultimately be useful for developing new methods to control chemical reactions.

Examining how a molecule responds to light on extremely fast timescales allows researchers to track how electrons move during a chemical reaction. “The big question is how a molecule dissipates energy without breaking apart,” said Enrico Ridente, a physicist at Berkeley Lab and lead author on the Science paper reporting the work. This means examining how excess energy is redistributed in a molecule that has been excited by light, as the electrons and nuclei move about while the molecule relaxes to an equilibrium state.

The researchers used the Cori and Perlmutter systems at the National Energy Research Scientific Computing Center (NERSC), a DOE Office of Science user facility at Berkeley Lab, to perform calculations that confirmed their measurements of the molecule’s movements.

“We can now explain how the molecule distorts after losing an electron and how the energies of the electrons respond to these changes,” said Diptarka Hait, a graduate student at Berkeley Lab and the lead theoretical author of the study.

2. Nanotechnology | Nanophysics | Nanomaterials

  • Optical metrology on an atomic scale
  • Application of AI deep learning to picophotonics, the science of light-matter interactions on the picometer scale

• > “Topologically structured light detects the position of nano-objects with atomic resolution” by Ingrid Fadelli, (May 19, 2023) – …

(image caption)
Mr. Cheng-Hung Chi, PhD student at the University of Southampton, uses superoscillatory light to detect the position of a nano-wire with atomic resolution. Credit: University of Southampton

Optical imaging and metrology techniques are key tools for research rooted in biology, medicine and nanotechnology. While these techniques have recently become increasingly advanced, the resolutions they achieve are still significantly lower than those attained by methods using focused beams of electrons, such as atomic-scale transmission electron spectroscopy and cryo-electron tomography.

In the team’s proof-of-principle experiments, their optical localization metrology method performed remarkably well, resolving the position of the suspended nanowire with a subatomic precision of 92 pm (i.e., around λ/5,300), while the nanowire naturally thermally oscillated with amplitude of ∼150 pm. For reference, a silicon atom is 220pm in diameter.

“We are now working on detecting picometer movements with a high frame rate, so we can shoot a video featuring the real dynamics of Brownian motion of a nanoscale object,” Zheludev [Nicolay I. Zheludev] added.

3. New microscopy technique, dubbed quantum microscopy by coincidence (QMC)

How does this work?

I’ve not encountered this perspective before: that a biphoton effectively has half the wavelength of single (classical) photon. The research teams’ apparatus apparently uses spontaneous parametric down-conversion, although SPDC is not mentioned (just references to signal & idler photons). “… a computer … builds an image of the cell based on the information carried by the signal photon.”

  • A paper (“Quantum Microscopy of Cells at the Heisenberg Limit”) in the journal Nature Communications (April 28, 2023)
  • “Because a biphoton [two entangled photons] has double the momentum of a photon, its wavelength is half that of the individual photons [which results in increased resolution.].”
  • “… one of the paired [entangled] photons passes through the object being imaged and the other does not. … Amazingly, the paired photons remain entangled as a biphoton behaving at half the wavelength despite the presence of the object and their separate pathways.”

• Caltech > News > “Quantum Entanglement of Photons Doubles Microscope Resolution” by Emily Velasco (May 1, 2023) – Using a “spooky” phenomenon of quantum physics, Caltech researchers have discovered a way to double the resolution of light microscopes.

[Shorter and shorter wavelengths of laser light carry more energy …] So, once you get down to light with a wavelength small enough to image tiny things, the light carries so much energy that it will damage the items being imaged, especially living things such as cells.

QMC gets around this limit by using biphotons that carry the lower energy of longer-wavelength photons while having the shorter wavelength of higher-energy photons.

“Cells don’t like UV light,” Wang [Lihong Wang, Bren Professor of Medical Engineering and Electrical Engineering, Caltech] says. “But if we can use 400-nanometer light to image the cell and achieve the effect of 200-nm light, which is UV, the cells will be happy, and we’re getting the resolution of UV.”

Wang’s lab was not the first to work on this kind of biphoton imaging, but it was the first to create a viable system using the concept. “We developed what we believe a rigorous theory as well as a faster and more accurate entanglement-measurement method. We reached microscopic resolution and imaged cells.”

Wang says future research could enable entanglement of even more photons [“multiphotons”], although he notes that each extra photon further reduces the probability of a successful entanglement, which, as mentioned above, is already as low as a one-in-a-million chance.

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