MIT News October 18, 2021 A team of researchers in the US (Stanford University, University of Chicago, Columbia University, MIT) constructed a network of artificial neurons comprising an input layer, a compression layer, and an expansion layer — just like the fruit fly olfactory system. They gave it the same number of neurons as the fruit fly system, but no inherent structure: connections between neurons would be rewired as the model learned to classify odors. The scientists asked the network to assign data representing different odors to categories, and to correctly categorize not just single odors, but also mixtures of […]
Cooling radio waves to their quantum ground state
Phys.org October 15, 2021 In standard cryogenic systems thermal decoherence prevents access to the quantum regime for photon frequencies below the gigahertz domain. An international team of researchers (the Netherlands, Germany) engineered two superconducting LC circuits coupled by a photon-pressure interaction and demonstrated sideband cooling of a hot radio frequency (RF) circuit using a microwave cavity. Because of a substantially increased coupling strength, they obtained a large single-photon quantum cooperativity and reduced the thermal RF occupancy by 75% with less than one pump photon. For larger pump powers, the coupling rate exceeds the RF thermal decoherence rate by a factor […]
Intelligent optical chip to improve telecommunications
Phys.org October 15, 2021 An international team of researchers (Canada, France, China, Australia) developed and demonstrated a self-adjusting on-chip optical pulse-shaper based on the concept of temporal coherence synthesis. The scheme enables on-the-fly reconfigurability of output optical waveforms by using an all-optical sampling technique in combination with an evolutionary optimization algorithm. They showed that particle-swarm optimization can outperform more commonly used algorithms in terms of convergence time. The system combines all key ingredients for realizing fully on-chip smart optical waveform generators for next-generation applications in telecommunications, laser engineering, and nonlinear optics. The team’s next steps include the investigation of more […]
Making progress towards quantum technologies based on magnetic molecules
Nanowerk October 15, 2021 Electrical control of spins at the nanoscale offers significant architectural advantages in spintronics. However, the electric-field sensitivities reported so far are rather weak. An international team of researchers (UK, Spain) showed that one path is to identify an energy scale in the spin spectrum that is associated with a structural degree of freedom with a substantial electrical polarizability. They studied an example of a molecular nanomagnet in which a small structural distortion establishes clock transitions in the spin spectrum; the fact that this distortion is associated with an electric dipole allowed them to control the clock-transition energy […]
Molecular interfaces for innovative sensors and data storage devices
Nanowerk October 20, 2021 To better understand electronic and magnetic properties and understanding the mechanisms that govern the interactions at the interface an international team of researchers (Germany, Austria, Switzerland, Italy) coupled nickel-porphyrin with copper. Using theoretical and experimental spectro-microscopy approach they showed that the charge transfer occurring at the interface between nickel tetraphenyl porphyrins and copper changes both spin and oxidation states of the Ni ion. The chemically active Ni(I), even in a buried multilayer system, can be functionalized with nitrogen dioxide, allowing a selective tuning of the electronic properties of the Ni center that is switched to a […]
New metalens focuses light with ultra-deep holes
Nanowerk October 13, 2021 Most metasurfaces use monolith-like nanopillars to focus, shape and control light. The taller the nanopillar more versatile control of each color of light. But very tall pillars tend to fall or cling together. Researchers at Harvard University developed a metasurface with more than 12 million needle-like holes drilled into a 5-micrometer silicon membrane rather than very tall pillars to focus light to a single spot. The diameter of these long, thin holes is only a few hundred nanometers, making the aspect ratio nearly 30:1. The hole size variation bends the light towards the lens focus. Holes […]
Quantum material to boost terahertz frequencies
Science Daily October 20, 2021 An international team of researchers (Germany, Spain, Russia) investigated the ultrafast carrier dynamics in topological insulators (TIs) of the bismuth and antimony chalcogenide family, where they isolated the response of Dirac fermions at the surface from the response of bulk carriers by combining photoexcitation with below-bandgap terahertz (THz) photons and TI samples with varying Fermi level, including one sample with the Fermi level located within the bandgap. They identified distinctly faster relaxation of charge carriers in the topologically protected Dirac surface states, compared to bulk carriers and they observed THz harmonic generation without any saturation […]
Scientists develop novel ‘shapeshifting’ liquid crystal
Phys.org October 19, 2021 A team of researchers in the US (Case Western reserve University, Tufts University, Sandia National Laboratory) manipulated an “orientable Newtonian liquid,” in this case to a nematic liquid crystal that behaves predictably, i.e., linearly, when an outside stimulus is applied. They forced the liquid crystal/air interface to change shape merely by exploiting the orientability of the molecules that comprise the liquid crystal by placing a patterned substrate on the opposite side of a thin nematic film. By doing so, they were able to control the alignment of molecules throughout the material which resulted in the appearance […]
Tuning transparency and opacity
Phys.org October 18, 2021 Recently, a new type of wavefront shaping was introduced where the extinction is manipulated instead of the scattered intensity. The underlying idea is that upon changing the phases or the amplitudes of incident beams, the total extinction will change due to interference described by the cross terms between different incident beams. Researchers in the Netherlands have experimentally demonstrated the mutual extinction and transparency effects in scattering media a human hair and a silicon bar. They sent two light beams with a variable mutual angle on the sample. Depending on the relative phase of the incident beams, they […]
Ultrafast control of quantum materials
Phys.org October 18, 2021 An international team of researchers (USA – Brown University, University of Pennsylvania, Germany, Switzerland) reviews recent progress in utilizing ultrafast light-matter interaction to control the macroscopic properties of quantum materials. Particular emphasis is placed on photoinduced phenomena that do not result from ultrafast heating effects but rather emerge from microscopic processes that are inherently nonthermal in nature. Many of these processes can be described as transient modifications to the free energy landscape resulting from the redistribution of quasiparticle populations, the dynamical modification of coupling strengths, and the resonant driving of the crystal lattice. Other pathways result […]