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Crown nanoplatelets

In recent years, scientists have been experimenting with combining semiconductors at the nanoscale, creating new nanostructures with interesting optoelectronic properties. Among the different colloidal nanostructures that can be made are 2D nanoplatelets, named for their thin tray-like shapes when seen through an electron microscope. They combine strong and weak quantum confinement regimes--which, on the one hand, yield a band-edge emission peak at discrete wavelengths; and on the other hand, yield a large band-edge oscillator strength and fast emission lifetime that scales with the area of the nanoplatelet.

The thickness can be controlled with monolayer precision. They also exhibit a high, two-photon absorption coefficient, and the 2D shape leads to opportunities for self-assembly and ultrafast Förster energy transfer between the nanoplatelets. These properties allow them to be tuned for a variety of optoelectronic tasks.

A variety of cadmium-based nanoplatelet heterostructures have been synthesized. Scientists have discovered that one can laterally extend the nanoplatelets by growing a second material around the edges, creating a so-called core/crown configuration. Prof. Dan Oron’s group, in the Department of Physics of Complex Systems, with collaborators in Belgium, created a number of different core/barrier/crown nanoplatelets and explored their optoelectronic properties. They showed that the core/barrier/crown structure enables two-photon fluorescence up-conversion and — due to a high nonlinear absorption cross section — even allows them to up-convert three near-infrared photons into a single green photon. These results demonstrate the versatility of 2D nanoplatelets in achieving unique optoelectronic properties.

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An ion-photon SWAP gate

Prof. Dayan’s group in the Department of Chemical and Biological Physics devised a scheme for an ion-photon qubit exchangethat would work like a SWAP gate found in conventional computing, which swaps one bit of information for another. Cavity quantum electrodynamics (cavity QED) devices manipulate the interaction between light confined in a reflective cavity and atoms, or other particles, under conditions where the quantum nature of light is significant. The Dayan team developed a quantum SWAP gate that is based on cavity-QED systems made with trapped ytterbium (Yb-171+), calcium (Ca-40+) and barium (Ba-138+) ions. The proposed gate can also serve as a single-photon quantum memory, in which an outgoing photon heralds the successful arrival of the incoming photonic qubit. The scientists were able to define the optimal parameters for the gate’s operation and simulate the expected fidelities and efficiencies. Their work demonstrates that efficient photon-ion qubit exchange, a valuable building block for scalable quantum computation, is practically attainable with current experimental capabilities.

Single beam, low frequency Raman spectrometry

Raman spectroscopy, named after the Indian physicist C. V. Raman, is a widely used spectroscopic technique to provide a structural fingerprint of molecules. Working with Prof. Yaron Silberberg (who sadly passed away in 2019) and his team, Prof. Dudovich and her group developed a new technique for low frequency Raman spectroscopy. Low frequency Raman spectroscopy is used to resolve the slow vibrations resulting from collective motions of molecular structures. In recent years, it has shed light on the molecular structure and bonds between atoms, and has been used to examine the dynamics of biomolecules such as hemoglobin.
The new approach separates the pulse of a single laser beam into a spectrally shaped pump and a transform-limited probe, which can be distinguished by their polarization states. The combination of single beam excitation with delayed probing, enables them to achieve higher spectral resolution than current low frequency Raman methods.
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