Electrons in twisted graphene ‘freeze’ when heated

21 Apr 2021 Isabelle Dumé

Pomeranchuk effect in magic angle graphene, revealing an exotic transition between two phases. Credit: Weizmann Institute of Science

When most solids are heated, they melt into liquids. This behaviour makes sense in terms of entropy, or disorder: a liquid state is usually more disordered than a solid state, and higher temperatures mean that the particles within a material vibrate randomly with more energy. One exception, however, is helium-3. This isotope of helium solidifies on heating, because in its solid state, fluctuations in its atoms’ nuclear spin (or internal “rotation”) give it a higher entropy than its liquid counterpart. This phenomenon is known as the Pomeranchuk effect after the theoretical physicist Isaak Pomeranchuk, who predicted it in 1950.

 

Physicists find a brighter way to diagnose quantum states

15 Apr 2021 Chunyang Ding

Another dimension: High spatial modes of packets of light, such as the 20-dimensional qudit shown here, were used to rapidly test a new method for determining quantum states. (Courtesy: Markus Rambach)

As scalable quantum computers move closer to reality, researchers need better ways of measuring and controlling the delicate systems that comprise them. One method, known as quantum state tomography, uses repeated measurements across the entire system to reveal the quantum state. However, this powerful diagnostic tool becomes impractical as quantum systems grow larger because in its conventional form, the number of measurements required increases exponentially with the size of the system. Now, researchers at the University of Queensland have applied a “self-guided” tomography method that more easily determines the quantum states encoded in the spatial shape of packets of light. This experiment opens the doors for using self-guided tomography on a wide array of quantum systems.

 

Fast electrons catch badly behaved quantum dots in the act

19 Apr 2021

Conditional behaviour: Atomic-scale observations show that quantum dots behave differently when exposed to higher- and lower-frequency light. (Courtesy: Greg Stewart/SLAC)

Quantum dots are responsible for the stunning, vibrant colours on modern TV screens, but they don’t always behave like they should. This creates headaches for device makers, who struggle to understand why some of these nanometre-scale semiconducting crystals shine much more dimly than others.

 

X-ray emissions from Uranus are detected for the first time

19 Apr 2021

Pastel planet: composite image of Neptune showing optical light (blue and white) and X-ray emissions (pink). (Courtesy: NASA/CXO/University College London/W Dunn et al/WM Keck Observatory)

Astronomers have spotted X-ray emissions from the planet Uranus for the first time. The international team, led by William Dunn at Mullard Space Science Laboratory in the UK, discovered the signals through new analysis of data from NASA’s Chandra X-ray Observatory. The observations could provide important guidance for upcoming X-ray studies of Uranus and Neptune.

X-ray emissions have been detected from most planets in the solar system and can originate from a variety of processes including the scattering of X-ray photons from the Sun; collisions between plasmas and planetary rings; and aurorae generated as solar winds interact with polar atmospheres. Until recently, however, evidence for X-ray emissions were notably absent from the solar system’s two ice giants: Uranus and Neptune.

 

Ultrafast ultrasound maps tiny blood vessels deep in the human brain

20 Apr 2021

Transcranial ultrafast ultrasound localization microscopy of deep brain vessels in a human patient. (Courtesy: Alexandre Dizeux/Physics for Medicine Paris)

Researchers at the laboratory Physics for Medicine Paris have performed the first microscopic mapping of the vascular network in the human brain. The team used transcranial ultrafast ultrasound localization microscopy (ULM) of intravenously injected microbubbles to capture intracranial blood flow dynamics with a resolution of around 25 µm.

This breakthrough in ULM technology, described in Nature Biomedical Engineering, may help expand the fundamental understanding of brain haemodynamics and shed light on how vascular abnormalities in the brain are related to neurological diseases and disorders.

 

Majorana-based quantum computation gets a handy new platform

14 Apr 2021 Jacob Marks

Quasiparticle platform A visualization of the Fermi surface depicting the momenta of electrons in the newly identified quantum computing platform. (Courtesy: Ruixing Zhang)

The errors that arise from the volatile nature of quantum technologies are a major roadblock on the path to practical quantum computing. We can imagine getting past this blockade by driving straight through it, using a car built to withstand the impact: this is quantum error correction. Alternatively, we might try to drive around the obstacle, bypassing the original problem entirely. To that end, researchers are investigating Majorana fermions – curious quantum objects that are their own antiparticles and are thought to be naturally resilient to quantum errors.

 

Attosecond streaking clocks the ultrafast emission of Auger electrons

29 Jan 2021

Jitter free: artistic depiction of a self-referencing attosecond streaking experiment. The inherent delay between the emission of the two types of electron leads to a characteristic ellipse in the analysed data. In principle, the position of individual data points around the ellipse can be read like the hands of a clock to reveal the precise timing of dynamical processes. (Courtesy: Daniel Haynes/Jörg Harms)

The decay lifetime associated with the emission of Auger electrons from atoms has been measured to sub-femtosecond precision using a technique called self-referencing attosecond streaking. Daniel Haynes of the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg and an international team of scientists are the first to make such a measurement using an X-ray free electron laser (XFEL).

 

Molecular qubits stick around for longer

13 Mar 2021 Isabelle Dumé

Team members Yinqiu Dai and Zhifu Shi with the spectrometer they used in their experiments. Courtesy: X Rong

Researchers in China have shown that the spin of a molecular quantum bit (qubit) can remain coherent for more than 1 millisecond – long enough to perform 145 000 basic logic operations. This number, known as the qubit “figure of merit”, is 40 times higher than previously reported for this molecule, raising the chances that such qubits could be used in quantum computing applications as well as in biomedical imaging and quantum sensing.

Quantum computers can, in principle, solve certain problems much faster than classical computers because they exploit a quantum particle’s ability to be in a superposition of two or more states at the same time (as opposed to classical bits that have only 0 and 1 states).

 

Nanoparticle-based vaccine offers new approach to COVID-19 immunity

19 Mar 2021 Ben Lewis 

Jae Jung, from Cleveland Clinic's Global Center for Pathogen Research & Human Health, and collaborators have developed a promising new COVID-19 vaccine candidate. (Courtesy: Cleveland Clinic)

As the international effort to vaccinate the population against COVID-19 gathers pace, the demand for vaccine doses that can be used in all countries and climates is enormous. Researchers from Cleveland Clinic and Chungbuk National University have described a new vaccine candidate that triggers an immune response using antigens attached to nanoparticles, potentially bypassing the need for cold storage during delivery. They report their findings in mBio.

All vaccines approved to date cause an immune response against the same part of the SARS-CoV-2 virus: the receptor binding domain (RBD) of the spike protein.

 

Has a new particle called a ‘leptoquark’ been spotted at CERN?

23 Mar 2021 Hamish Johnston

Fleeting glance: decay of a beauty quark involving an electron and positron as observed by LHCb. (Courtesy: CERN)

A hint of the possible existence of a hypothetical particle called a leptoquark has appeared as an unexpected difference in how beauty quarks decay to create electrons or muons. Measured by physicists working on the LHCb experiment on the Large Hadron Collider (LHC) at CERN, the difference appears to violate the principle of “lepton universality”, which is part of the Standard Model of particle physics. The measurement has been made at a statistical significance of 3.1σ, which is well below the 5σ level that is usually considered a discovery. If the violation is confirmed, it could provide physicists with important clues about physics beyond the Standard Model – such as the existence of leptoquarks.

 

How sidewinder snakes slither sideways, the challenges of creating sustainable infrastructure

11 Feb 2021 Hamish Johnston

In this episode of the Physics World Weekly podcast we meet physicist Jennifer Rieser who has just moved from the Georgia Institute of Technology to Emory University, where she studies how snakes use tiny structures on their undersides to help propel themselves. Rieser talks about her recent research that suggests that microscopic pits on the bellies of sidewinder snakes help the reptiles achieve their sidewinding motion.

 

Graphene gives neural interfaces a boost, the amazing physics of hearing and vision

08 Apr 2021 Hamish Johnston

This episode of the Physics World Weekly podcast looks at how new technologies can improve our health and how we perceive our surroundings.

First up is Kostas Kostarelos of the UK’s University of Manchester, who talks about the exciting role that graphene can play in the development of medical devices that connect to the brain with minimal invasiveness. He also chats about his involvement with the Spanish company Inbrain Neuroelectronics, which is developing graphene-based technologies for treating epilepsy, Parkinson’s disease, and other brain related disorders.