Research Spotlight

Recent Press Releases:

Design, fabrication and characterization of a hybrid metal-dielectric nanoantenna with a single nanocrystal for directional single photon emission

In this work we detail the fabrication method of a hybrid metal-dielectric nanoantenna with a single nanocrystal quantum dot positioned in its center. We have recently shown in [Nano Lett.16, 2527 (2016)] that this device efficiently directs photons from the nanocrystal emission into a small divergence angle perpendicular to the nanoantenna surface. The fabrication method presented here is robust and can be fine-tuned by only a few parameters to achieve high yield of such nanostructures....

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Condensation to a strongly correlated dark fluid of two dimensional dipolar excitons

Fig. 1

​​Recently we reported on the condensation of cold, electrostatically trapped dipolar excitons in GaAs bilayer heterostructure into a new, dense and dark collective phase. Here we analyze and discuss in detail the experimental findings and the emerging evident properties of this collective liquid-like phase. We show that the phase transition is characterized by a sharp increase of the number of non-emitting dipoles, by a clear contraction of the fluid spatial extent into the bottom of the parabolic-like trap, and by spectral narrowing. We extract the total density of the condensed phase which we find to be consistent with the expected density regime of a quantum liquid. We show that there are clear critical temperature and excitation power onsets for the phase transition and that as the power further increases above the critical power, the strong darkening is reduced down until no clear darkening is observed. At this point another transition appears which we interpret as a transition to a strongly repulsive yet correlated e-h plasma. Based on the experimental findings, we suggest that the physical mechanism that may be responsible for the transition is a dynamical final-state stimulation of the dipolar excitons to their dark spin states, which have a long lifetime and thus support the observed sharp increase in density. Further experiments and modeling will hopefully be able to unambiguously identify the physical mechanism behind these recent observations....

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High-spatial-resolution mapping of catalytic reactions on single particles

Schematic representation of the experimental set-up.

The benefits of defects – Peering into the nanoscale world of catalysts

A recent study that was led by researchers from the Hebrew University of Jerusalem and UC Berkeley and was published in the journal “Nature”, uncovered the ways by which metallic nanoparticles, which are used as catalysts in numerous industrial processes, activate catalytic processes.

Catalysis is one of the fundamental pillars of the chemical industry. The preparation of many materials that are essential for our daily life in a modern society, such as plastics, fuels and fertilizers, heavily relies on the use of catalysts. Catalysts are essential since they can make chemical processes more efficient, less energy-demanding and reduce or even eliminate the use and generation of hazardous substances.

Catalysts are mostly constructed of metallic nanoparticles, which are made of precious metals, such as Platinum, Palladium or Rhenium. The small size of the nanoparticles maximizes their activity and efficiency. Although catalysts have been heavily used in the chemical industry for more than a century, there are many details about their structure-reactivity correlations which are not yet clear. This lack of knowledge is related to the small size of the particles which limits the ability to directly identify catalytic processes on single particles. If researchers could peer inside and monitor, at a nanoscopic level, the chemical reactions on single particle, they would gather a treasure of useful knowledge, which is required for the design of improved catalysts that can address the pressing energy needs of the 21st century....

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The Technology That Will Turn Your Smartphone Into an X-ray Machine

Dr. Ori Katz seeks to improve on what ultrasounds, CT and MRI scans can do.

The advanced technology is based on new theories which have shaken up conventional wisdom about what happens when light passes through a semi-opaque surface - like skin. If nothing else, new tech would be a hit among peeping toms, Israeli researcher Dr. Ori Katz jokes.

Imagine a smartphone app that can see through frosted glass, the kind protecting our privacy in bathrooms, and take sharp, clear photographs. Technology that can do just that is being developed by the Applied Physics Department at Hebrew University.
Dr. Ori Katz and his colleagues in the Advanced Imaging Unit have achieved distinct photographs of images beyond semi-opaque glass using a smartphone. Voyeurs wanting to peep are likely to make the advanced optical technology a hit; grant money probably won’t be a problem, he jokes.
Katz, however, has loftier goals in mind, such as medical imaging. For instance, seeing through tissue. Not to look at the naked body but inside it; to observe what happens beneath our skin, at resolution so high it’s microscopic....

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Quantum Leap: Scientists Demonstrate a Compact, Efficient Single Photon Source That Can Operate at Ambient Temperatures On a Chip
Highly directional single photon source concept is expected to lead to a significant progress in producing compact, cheap, and efficient sources of quantum information bits for future applications Quantum information science and technology has emerged as a new paradigm for dramatically faster computation and secure communication in the 21st century. At the...

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Pythagoras rules: Researchers at the Hebrew University of Jerusalem measure control of a four-level quantum system by geometrical tools

Figure 1
Pythagoras taught us a simple connection between the dimensions of a triangle. Now, thousands of years later, this connection is implemented for precise control over the quantum state of a superconducting circuit.

Quantum mechanics describes the behavior of light and matter in many important systems. However, in contrast with our every-day experience, the quantum state is fundamentally and disturbingly different. For example, a particle described by quantum theory can be simultaneously in two or more places or pass through walls.

The use of controlled quantum systems is at the forefront of research in Physics and Computer Science, attempting to build computers and communication systems utilizing this simultaneity. It is very common to work on simple quantum systems with just two possible states, similar to the classical bit in computers, but now with quantum simultaneity (qubit). The transition to more complex systems, with more quantum states, will require new theoretical and experimental tools for control and understanding.....

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A breakthrough in molecular electronics

Measurement set-up and sample image.
The central technological revolution of the 20th century is the development of computers, leading to the communication and internet era. The main measure of this evolution is and has always been miniaturization; making our machines smaller. In the 1970s a computer with the memory of the average laptop today, was the size of a tennis court. While we have come far in the reduction of the size of individual components of a computer through microelectronics, the distance between transistors, the main element of our computers, has been much more challenging and extremely expensive to miniaturize. This limits the future development of computers. Molecular electronics, which uses molecules as building blocks for the fabrication of electronic components, was seen as the ultimate solution to the miniaturization challenge. However, to date, no one has actually been able to make complex electrical circuits using molecules. The only known molecules that can be pre-designed to self-assemble into complex miniature circuits that could be used in computers, are DNA molecules. Nevertheless, so far no one has been able to demonstrate reliably and quantitatively the flow of electrical current through long DNA molecules.

In a paper published this week in the prestigious journal Nature Nanotechnology, an international group of scientists, led by Prof. Danny Porath of The Hebrew University of Jerusalem, reports reproducible and quantitative measurements of electricity flow through long molecules made of four DNA strands. These findings signal the most significant breakthrough towards the development of DNA-based electrical circuits in the last 10 years.

The molecules were produced by the group of Alexander Kotlyar from Tel Aviv University, who has been collaborating with Porath for 15 years. The measurements were performed mainly by Gideon Livshits, a PhD student in the Porath group, who carried the project forward with great creativity, initiative and determination. The research was carried out in collaboration with groups from Denmark, Spain, US, Italy and Cyprus.
This pioneering research from the HU paves an original way towards a new generation of computer circuits that can be more sophisticated, cheaper and simpler to make.....

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