Volume 19 Issue 9, September 2023

Claims of a room-temperature, ambient-pressure superconductor recently kicked up a storm on social media. As the dust settles, we take stock of what this experience can teach us.

Laser cooling of neutral and positively charged ions is well mastered, but cooling of anions remains largely unexplored. Now, laser-induced evaporative cooling of negatively charged molecules has been achieved.

Determining the melting temperature and electrical conductivity of ammonia under the internal conditions of the ice giants Uranus and Neptune is helping us to understand the structure and magnetic field formation of these planets.

Hydrides are promising for harnessing high-temperature superconductivity, albeit with the need of extreme pressures. New experimental protocols establish a magnetic route to detect and study superconductivity compatible with high-pressure devices.

Whether Anderson localization of light is possible in three dimensions has long been an open question. Numerical calculations have now shown that it can be done with a disordered arrangement of metal particles.

The interplay of quantum measurements and local interactions in many-body systems can lead to new out-of-equilibrium phase transitions. An experiment has now shown that quantum simulators can meet the challenge of detecting them.

A real qubit is not an isolated unitary quantum system but is subject to noise from its environment. An experiment has now turned this interaction on its head, controlling the environment using the qubit itself.

Multi-colour light fields allow a nonlinear coupling between free electrons and propagating light by stimulated Compton scattering, without the need for near fields to mediate the interaction.

Regenerative animals accurately regrow lost appendages. Now, research suggests that mechanical waves propagating from the amputation edge have a key role in this process.

Calculations support experiments in predicting the existence and properties of point defects in solids but often do not correctly capture their details. A different method can significantly improve the prediction of defect structures and properties.

A coherent interface between a mechanical oscillator and superconducting electrical circuits would enable the control of quantum states of mechanical motion, but such interfaces often result in excess mechanical energy loss. A new material-agnostic approach is shown to achieve strong electromechanical coupling while preserving a long phonon lifetime.

Describing interdependencies and coupling between complex systems requires tools beyond what the framework of single networks offers. This Review covers recent developments in the study and modelling of multilayer networks.

Vibrational spectroscopy of molecular hydrogen ions is used to search for deviations from conventional quantum physics, but none are found.

A common technique to cool down molecular ions is through collisions with a buffer gas, but that is limited by the achievable temperature of the medium. Now, an experiment demonstrates the evaporative cooling of molecular ions below previously reached temperatures.

The realization of cold and dense electron–hole systems by optical excitation is hindered by the heating caused by particle recombination. Now, cold and dense electron–hole systems have been observed in heterostructures with separated electron and hole layers.

Laser-driven shock compression experiments yield the melting curve of the superionic phase of ammonia at conditions relevant to the interiors of Uranus and Neptune.

Strong dipole–dipole interactions between excitons in a moiré superlattice create a manifestation of the Bose–Hubbard model with a ground state similar to a Mott insulator.

Measurements of the trapped magnetic flux in hydrides at high pressure provide further evidence that these materials are superconducting at high temperatures.

How the superconducting state emerges from a Mott insulator in cuprate superconductors is still not fully understood. Now, the spatial extent of a chequerboard charge order with internal stripes is shown to be crucial.

Whether Anderson localization of light can be achieved in three dimensions has remained an open question. Numerical calculations now show that it is possible with a random arrangement of metallic spheres, but not with dielectric ones.

The interplay of quantum measurements and unitary evolution is expected to produce dynamical phases with different entanglement properties. An entanglement phase transition has now been detected with hybrid quantum circuits in a superconducting processor.

The performance of superconducting qubits is often limited by spurious two-level systems. Now, a qubit operating as a heat engine manipulates its bath of nearby two-level systems, providing insights into their dynamics and interactions.

Electrical control of quantum mechanical oscillators is normally performed using piezoelectrics, but incorporating these additional materials can severely reduce performance. Electrostatic control has now been demonstrated in a silicon device.

Analogue photonic simulators have so far suffered from severe finite size effects and limited programmability. Now, a frequency-mode photonic simulator enables the simulation of large-scale models in two and three dimensions.

Although mechanical resonators are routinely cooled to their quantum ground state, it has remained unclear if sizable nonlinearities could persist there. Experiments in the ultrastrong-coupling regime now show that this is possible.

Some driven systems sustain non-equilibrium phases in which phase transitions occur without symmetry breaking. The use of a laser-cooled atomic cloud confined in a pencil beam now allows the demonstration of such a system.

Although massive electrons and massless photons are known to interact, their study has so far been confined to the linear regime. Experiments showing two-photon coherent control of a free-electron matter wave now introduce non-linearities.

Active matter exhibits positional coherence in addition to the well-known orientational order. It is now shown that coherent structures in active nematics—made of dynamical attractors and repellers—form, move and deform, steered by topological defects.

It is known that mechanical waves play a role in collective motion in vitro. Now these waves can help an amputated zebrafish know where its fin was cut off to aid regeneration.

Originally invented to improve cornering techniques in race driving, speed traps contribute to road safety. Robert Wynands introduces us to tools of traffic metrology.