The study was conducted in the research group of Professor Erez Hasman, head of the Atomic-Scale Photonics Laboratory, in collaboration with Professor Elad Koren, head of the Laboratory for Nanoscale Electronic Materials and Devices in the Department of Materials Science and Engineering, and Professor Ariel Ismach at Tel Aviv University. The two groups at the Technion are in association with the Helen Diller Quantum Center and Russell Berrie Nanotechnology Institute (RBNI). Dr. Kexiu Rong conducted and led the research, and collaborated with Dr. Xiaoyang Duan, Dr. Bo Wang, Dr. Vladimir Kleiner, Dr. Assael Cohen, Dr. Pranab K. Mohapatra, Dr. Avinash Patsha, Dr. Subhrajit Mukherjee, Dror Reichenberg, Chieh-li Liu, and Vladi Gorovoy.

Can we lift the spin degeneracy of light sources in the absence of magnetic fields at room temperature? According to Dr. Rong, “Spin-optical light sources combine photonic modes and electronic transitions and therefore provide a way to study the exchange of spin information between electrons and photons and to develop advanced optoelectronic devices. To construct these sources, a prerequisite is to lift the spin degeneracy between the two opposite spin states either in their photonic or electronic parts. This is usually accomplished by applying magnetic fields under a Faraday or Zeeman effect, although these approaches generally require strong magnetic fields and cannot produce miniaturized sources. Another promising way takes advantage of artificial magnetic fields for photonic spin-split states in momentum space, underpinned by a geometric phase mechanism.

Unfortunately, previous observations of spin-split states have relied heavily on propagation modes with low quality factors, which impose undesired limitations on spatial and temporal coherence of the sources. This approach is also hindered by the spin-controllable properties of a bulk laser gain material being unavailable or nontrivial to access for active control of the sources, especially in the absence of magnetic fields at room temperature.”

To achieve high-Q spin-split states, the researchers constructed photonic spin lattices with different symmetry properties, which comprise an inversion-asymmetry core and inversion-symmetry cladding integrated with a WS₂ monolayer to create laterally confined spin-valley states. The essential inversion-asymmetry lattice the researchers use has two important properties. (1) A controllable spin-dependent reciprocal lattice vector due to space-variant geometric phases from its constituting inhomogeneous-anisotropic nanoholes. This vector splits a spin-degenerate band into two spin-polarized branches in momentum space, being referred to as the photonic Rashba effect. (2) A pair of high-Q symmetry-enabled (quasi-) bound states in the continuum, that is, ±K (corners of the Brillouin zone) photonic spin-valley states, at the band edges of the spin-split branches. Moreover, the two states form a coherent superposition state with equal amplitudes.

Professor Koren noted that, “We used a WS₂ monolayer as the gain material because this direct-bandgap transition metal dichalcogenide possesses unique valley pseudospins, which have been widely investigated as an alternative information carrier in valleytronics. Specifically, their ±K’ valley excitons (radiated as in-plane spin-polarized dipole emitters) can be selectively excited by spin-polarized light according to a valley-contrasted selection rule, thus enabling active control of spin-optical light sources without magnetic fields.”

In the monolayer-integrated spin-valley microcavities, ±K’ valley excitons couple to ±K spin-valley states owing to polarization matching, and spin-optical excitonic lasing is achieved at room temperatures through strong optical feedback. Meanwhile, ±K’ valley excitons (initially without a phase correlation) are driven by the lasing mechanism to find the minimum-loss state of the system, which leads them to re-establish a phase-locked correlation according to the opposite geometric phases of ±K spin-valley states. This lasing-mechanism-driven valley coherence removes the need for cryogenic temperatures to suppress the intervalley scattering. Moreover, the minimum-loss state of the Rashba monolayer laser can be regulated to be satisfied (broken) via a linear (circular) pump polarization, which provides a way to control the lasing intensity and spatial coherence.

“The unveiled photonic spin valley Rashba effect provides a general mechanism to construct surface-emitting spin-optical light sources. The demonstrated valley coherence in the monolayer-integrated spin-valley microcavity makes a step towards achieving entanglement between ±K’ valley excitons for quantum information by means of qubits,” explains Professor Hasman. “For a long time, our group has been working on developing spin optics to harness photonic spin as an effective tool to control the behavior of electromagnetic waves. In 2018, we were attracted by valley pseudospins in two-dimensional materials, and therefore began a long-term project to study the active control of atomic-scale spin-optical light sources in the absence of magnetic fields. We initially tackled the challenge of coherent geometric phase pickup from individual valley excitons by using a non-local Berry-phase defect mode.

However, the underlying coherent addition of multiple valley excitons of the realized Rashba monolayer light sources remained unsolved, owing to the lack of a strong synchronizing mechanism between the excitons. This issue inspired us to think about high-Q photonic Rashba modes. Following innovations in new physical approaches, we achieved the Rashba monolayer laser described here.”

The research was supported by the Israel Science Foundation (ISF), the Helen Diller Foundation and the joint Technion NEVET grant by RBNI. The fabrication was performed at the Micro-Nano Fabrication & Printing Unit (MNF&PU) of the Technion.

The study focuses on a question that still generates debate among neuroscientists: whether infants who have not yet learned to speak (or are developing speech) are capable of logical reasoning. This pioneering research shows that this natural logical reasoning exists from at least 19 months of age, does not depend on knowledge of language and is developed mainly through the strategy of exclusion by elimination. In other words, if toddlers are faced with an unknown reality, they would try to analyse it and reach some conclusion about it by ruling out the options that are not possible, according to their level of knowledge at the time.

The results of the paper are presented in the article entitled The scope and role of deduction in infant cognition, written by Kinga Anna Bohus, Nicolo Cesana-Arlotti, Ana Martín-Salguero and Luca Lorenzo Bonatti. The principal researcher, L. Bonatti (ICREA), is the director of the Reasoning and Infant Cognition (RICO) research group at the Center for Brain and Cognition (CBC) at UPF. Kinga Anna Bohus (main author) also belongs to the group. N. Cesana-Arlotti and Ana Martín-Salguero, previously linked to the CBC at UPF, are currently researchers at Yale University (USA) and at the École Normale Supérieure in Paris.

Toddlers tend to solve uncertainties by ruling out impossible options according to the level of knowledge they have at any given moment

The study analyses the importance of two strategies for infants to deal with uncertainties: association and exclusion (or disjunction elimination). The first strategy would mean that toddlers hearing a new word that may refer to two unfamiliar objects that they can see, mentally associate the term with each of them. Subsequently, they would associate the term with the object with which this name fits better.

The second strategy (exclusion) explains how a toddler can learn a new word through logical reasoning by eliminating alternatives. For example, if they see two objects (A and B) and hear an unknown term that they know is not A (because they know the name of A), they will determine that it is the name of B. This is the predominant strategy, according to the results of the study.

Two experiments to analyse toddlers’ natural logic posed with known and unknown objects and terms

The research team conducted two different experiments, the first with 61 monolingual (26) and bilingual (35) 19-month-old toddlers and the second with 33 (19 mono and 14 bilingual). The analysis of each group was crucial to determine whether deductive processes depend on linguistic experience.

In the first experiment, the participants were shown two objects, which they had to associate with one of the words they heard, through different tests. In the first test, they had to look at two objects they knew (e.g., a spoon and a biscuit) and, upon hearing a term (e.g., spoon), associate it with one of the two. In the second test, the infants were shown an object they knew (e.g., an apple) and an object they did not know (e.g., a carburettor), and they heard the word corresponding to the known object (apple), which they had to identify. The third test was the same as the second, except that the word heard corresponded to the unknown word (e.g., carburettor).

In the second experiment, two objects or animate beings were used (for example, an umbrella and a figure of a boy), each associated with a sound. Subsequently, the two objects were covered so that the infant could not see them and one of them was placed in a glass. When they were uncovered, the toddler could only see one of the two objects and had to guess, by elimination, which one was inside the glass. In a subsequent test (with the two objects covered and without changing their position), the infant listened to the sound associated with one of them and it was analysed whether he/she looked in the direction of the correct object.

In all these tests, their gaze movement patterns were assessed. For example, when reasoning by exclusion, toddlers look at object A and, if they rule out that the term they have heard refers to it, then they turn their gaze towards B. This is known as the double check strategy.

There are no relevant differences in the logic of monolingual and bilingual toddlers

The main author of the research, Kinga Anna Bohus, summarizes the main findings of the study as follows: “We studied the presence of the concept of logical disjunction in 19-month-old infants. In a word-referent mapping task, both bilingual and monolingual infants display a pattern of oculomotor inspection previously found to be a hallmark of disjunctive reasoning in adults and children.”

In short, the results of the study show no relevant differences between the logical reasoning of monolingual and bilingual toddlers, which confirms that it does not depend on linguistic knowledge. This natural logical thinking could be present before the age of 19 months, although there is still not enough scientific evidence to demonstrate its presence at earlier ages.

The team of chemistry professor Claudia Höbartner from Julius-Maximilians-Universität (JMU) Würzburg now presents a newly discovered ribozyme called SAMURI in the journal Nature Chemistry.

SAMURI can precisely modify other RNA molecules. This ability is very helpful for RNA research: “We can use such ribozymes as tools to label RNA with dyes and make it visible,” says JMU researcher Dr. Takumi Okuda. “In this way, the pathways of RNA in the cell and its interactions with other molecules can be studied even better.”

Ribozymes may also be considered for therapeutic use in the future. “We see new possible applications for ribozymes when the enzymes responsible for a specific task are missing or are no longer functional due to mutations,” says Claudia Höbartner.

Details about the new ribozyme

What distinguishes the new ribozyme SAMURI? It modifies other RNA molecules at a precisely defined site of a specific adenine. There it attaches molecules to which, in turn, dyes or other molecules can easily be clicked in — like buckling up a seat belt. Such reactions are known as click chemistry.

SAMURI also has the advantage that it is active under the same physiological conditions that prevail in living cells. This is not the case with other synthetic ribozymes.

Another special feature: SAMURI uses a new synthetic cofactor to make RNA molecules accessible for click chemistry. This cofactor was developed by Dr. Takumi Okuda; it was inspired by the ubiquitous natural cofactor SAM (S-adenosylmethionine). This is also where the name of the new ribozyme comes from: SAMURI stands for “SAM-analogue utilising ribozyme.”

The following steps in research

Claudia Höbartner’s group next wants to elucidate the structure and mechanism of action of SAMURI. She also wants to develop further ribozymes that can modify RNA building blocks other than adenine.

“Who can explain why one species ranges widely and is very numerous, and why another allied species has a narrow range and is rare?” This question was asked by Charles Darwin in his ground-breaking book “The Origin of Species,” published over 150 years ago. A related challenge has been to understand how many species are common (numerous) and how many are rare, the so-called global species abundance distribution (gSAD).

Two main gSAD models have been proposed in the last century: R. A. Fisher, a statistician and biologist, proposed that most species are very rare and that the number of species declines for more common species (so-called log-series model). On the other hand, F. W. Preston, an engineer and ecologist, argued that only few species are actually very rare and that most species have some intermediate level of commonness (so-called log-normal model). However, until now and despite decades of research, scientists did not know which model describes the planet’s true gSAD.

Solving this problem calls for vast amounts of data. The study authors used data from the Global Biodiversity Information Facility (GBIF) and downloaded data representing over 1 billion species observations in nature from 1900 to 2019.

“The GBIF database is an amazing resource for all sorts of biodiversity related research, particularly because it brings together both data collected from professional and citizen scientists all over the world,” says first author Dr Corey Callaghan. He began the study while working at iDiv and MLU and is now working at the UF.

Callaghan and his fellow researchers divided the downloaded data into 39 species groups, for instance, birds, insects, or mammals. For each, they compiled the respective global species abundance distribution (gSAD).

The researchers detected a potentially universal pattern, which emerges once the species abundance distribution is fully unveiled: Most species are rare but not very rare, and only a few species are very common, as predicted in the log-normal model. However, the researchers also found that the veil has been fully lifted only for a few species groups like cycads and birds. For all other species groups, the data are yet insufficient.

“If you don’t have enough data, it looks as though most species are very rare,” says senior author Prof Henrique Pereira, research group head at iDiv and the MLU. “But by adding more and more observations, the picture changes. You start seeing that there are, in fact, more rare species than very rare species. You can see this shift for cycads and birds when comparing the species observations from back in 1900, when less data was available, with the more comprehensive species observations we have today. It is fascinating: we can clearly see the phenomenon of unveiling the full species abundance distribution, as predicted by Preston several decades ago, but only now demonstrated at the scale of the entire planet.”

“Even though we have been recording observations for decades, we have only lifted the veil for a few species groups,” says Callaghan. “We still have a long way to go. But GBIF and the sharing of data really represents the future of biodiversity research and monitoring, to me.”

The new study’s findings enable scientists to assess how far the gSADs have been unveiled for different species groups. This allows for answering another long-standing research question: How many species are out there? This study finds that while for some groups like birds, nearly all species have been identified, this is not the case for other taxa such as insects and cephalopods.

The researchers believe that their findings may help in answering Darwin’s question of why some species are rare, and others are common. The universal pattern they found may point to general ecological or evolutionary mechanisms that govern the commonness and rarity of species. While more research is being done, humans continue to alter the planet’s surface and the abundance of species, for instance, by making common species less common. This complicates the researchers’ task: They need not only to understand how species abundances evolve naturally but also how human impacts are altering these patterns simultaneously. There may still be a long way to go before Darwin’s question is finally answered.