Volume 19 Issue 11, November 2023

The 2023 Nobel Prize in Physics has been awarded to Pierre Agostini, Ferenc Krausz and Anne L’Huillier “for experimental methods that generate attosecond pulses of light for the study of electron dynamics in matter”.

Renormalization began as a tool to eliminate divergences in quantum electrodynamics, but it is now the basis of our understanding of physics at different energy scales. Here, I review its evolution with an eye towards physics beyond the Wilsonian paradigm.

Kenneth Wilson worked on the renormalization group during the Cold War, when communication between scientists in the Soviet Union and in the West was restricted. Nevertheless, Soviet physicists had a strong influence on Wilson’s work.

The correct microscopic theory of quantum gravity may be an interacting, scale-invariant, ‘asymptotically safe’ model. This Comment discusses the renormalization group’s role in defining asymptotic safety and understanding its consequences.

Supersymmetric quantum field theories have special properties that make them easier to study. This Comment discusses how the constraints that supersymmetry places on renormalization group flows have been used to study strongly coupled field theories.

The renormalization group is a key ingredient in methods of improving perturbative computations in particle physics. Here I briefly discuss its role in perturbative quantum chromodynamics and particularly the running of its coupling constant.

Historically, most renormalization group studies have been performed for equilibrium systems. Here, I give a personal reflection on the unexpected outcome of studying non-equilibrium flocking using renormalization methods.

The renormalization group evolved from ad hoc procedures to cope with divergences in perturbative calculations. This Comment summarizes efforts to develop a mathematically rigorous approach to renormalization group calculations.

A new binding mechanism between trapped laser-cooled ions and atoms has been observed. This advancement offers a novel control knob over chemical reactions and inelastic processes on the single particle limit.

Chains of coupled superconducting islands known as Josephson junction arrays were predicted to be insulating at high impedance, but superconducting behaviour has been observed. A study of the arrays’ transport suggests thermal effects are responsible.

The near-zero thermal expansion of Invar alloy Fe₆₅Ni₃₅ is technologically important but still unexplained. Measurements show that this phenomenon can be explained by the cancellation of magnetic and phonon contributions to the alloy’s entropy.

A detailed understanding of phonon transport is crucial for engineering the thermal properties of materials. A particular doping strategy is now shown to lead to good thermoelectric performance with low thermal conductivity.

The guiding of magnetic fields by soft ferromagnetic solids is well known and exploited in magnetic shielding applications. Now, ferroelectric nematic liquids are shown to analogously guide electric fields.

Currently, a general framework explaining the fundamental dynamic transitions from solid to fluid of mechanically probed soft materials is lacking. Now, a unifying van der Waals-like model is proposed that describes the dynamic solid–liquid transition in the rheology of these materials.

Generating high harmonics or attosecond pulses of light is normally thought of as a classical process, but a theoretical study has now shown how the process could be driven by quantum light.

A milestone for the coherence time of a macroscopic mechanical oscillator may be a crucial advance for enabling the development of quantum technologies based on optomechanical architectures and for fundamental tests of quantum mechanics.

Time-varying photonics offers ways to manipulate light–matter interactions as never thought before. An experiment with photonic time interfaces reveals how they can enable broadband coherent control of waves.

Measuring the transmission matrix of disordered structures has so far been limited to the domain of linear systems. Now it has been measured for nonlinear disorder, with exciting implications for information capacity.

Drops sitting on an array of parallel fibres spontaneously move along the fibres when subject to an airflow perpendicular to the array. The drops show long-range aerodynamic interactions with their downstream and upstream neighbours, and these can catalyse drop coalescence and removal of drops from the fibres — relevant for applications such as fog harvesting and filtration.

Many applications of ultracold molecules require high densities that have been difficult to reach. An experiment now demonstrates the tight magnetic confinement of ultracold molecules, enabling the study of molecular collisions in the quantum regime.

The formation of molecules in binary particle collisions is forbidden in free space, but the presence of an external trapping potential now enables the realization of bound states in ultracold atom–ion collisions.

The high inelastic loss rate in gases of bosonic molecules has so far hindered the stabilization needed to reach quantum degeneracy. Now, an experiment using microwave shielding demonstrates a large reduction of losses for bosonic dipolar molecules.

Entangled states are a key resource for quantum-enhanced sensing. A protocol based on spin-nematic squeezed states of atomic Bose–Einstein condensates has now been used to achieve record metrological gains in nonlinear interferometry experiments.

Electronic nematic order as a distinct phase in kagome materials without any entanglement with charge density wave or charge stripe order has not been detected. Now, it is observed in a titanium-based kagome metal.

Cooper pairs that form with finite centre-of-mass momentum are rare. Now there is evidence that this can happen below the Pauli limit in a bilayer material.

YbRh₂Si₂ has a quantum phase transition between an antiferromagnetic phase and a so-called heavy-Fermi-liquid state. Measurements of critical slowing down suggest that the heavy-fermion quasiparticles break down at the transition.

Previous work has suggested that at very low temperatures TbInO₃ hosts an unconventional quantum ground state. Terahertz time-domain spectroscopy measurements of its excitations show that related exotic effects can persist to room temperature.

The three-dimensional spin textures of a skyrmion lattice have now been measured in a bulk material using a tomographic small-angle neutron scattering technique.

Geometric frustration and bond-dependent interactions each introduce quantum fluctuations that can create spin liquid phases. Now it is shown that CoI₂ is a triangular lattice material that combines both.

Predictions of a quantum superconductor–insulator transition in Josephson junction arrays are not always borne out by experiments. Unexpectedly large thermal effects may explain why.

The behaviour of a superconductor can be altered by changing its symmetry properties. Coherently coupling two Josephson junctions breaks time-reversal and inversion symmetries, giving rise to a device with a controllable superconducting diode effect.

The iron–nickel alloy Invar has an extremely small coefficient of thermal expansion that has been difficult to explain theoretically. A study of Invar under pressure now suggests that there is a cancellation of phonon and spin contributions to expansion.

Aliovalent doping affects the electrical properties of semiconductors, but its effect on phonons is unclear. Now, strong softening and deceleration of phonons, causing a significant reduction in lattice thermal conductivity, is reported for Hf-doped NbFeSb.

The ferroelectric uniaxial nematic liquid-crystal phase features a freely reorientable polarization field. When confined in microchannels and subjected to electric fields, this polarization is now found to align with the channels due to a superscreening effect.

The wetting behaviour of drops attached to fibres is exploited in many applications including fog harvesting. The presence of a background air flow on fibre-attached drops on parallel fibres is now shown to lead to alignment, repulsion and coalescence processes.

The yielding transition in concentrated colloidal suspensions and emulsions lacks a universal description. A unified state diagram is now shown to underlie yielding for these materials, analogous to the van der Waals phase diagram for non-ideal gases.

Colloidal aggregates are conventionally formed by particle aggregation under thermal fluctuation. Now the structure and mechanical properties of aggregates can be controlled by an active bath of swimming Escherichia coli.

High-harmonic generation is a source of high-frequency radiation and is typically driven by strong, but classical, laser fields. A theoretical study now shows that using quantum light states as the driver extends the spectrum of outgoing radiation in a controllable manner.

Achieving low decoherence is challenging in hybrid quantum systems. A superconducting-circuit-based optomechanical platform realizes millisecond-scale quantum state lifetime, which allows tracking of the free evolution of a squeezed mechanical state.

Coherent control is an interference technique widely used to control dynamic wave processes. Its analogue in the time domain allows the tailored suppression, enhancement and reshaping of optical pulses, and the mimicking of collisions between them.

Disordered media with their numerous scattering channels can be used as optical operators. Measurements of the scattering tensor of a second-harmonic medium extend this computing application to the nonlinear regime.

Quantum computers are believed to exponentially outperform classical computers at some tasks, but it is hard to make guarantees about the limits of classical computers. It has now been proven that classical computers cannot efficiently simulate most quantum circuits.

Being able to perform qubit measurements within a quantum circuit and adapt to their outcome broadens the power of quantum computers. These mid-circuit measurements have now been used to implement a cryptographic proof of non-classical behaviour.

Although its measurement was considered an experimental nightmare for decades, the Stefan–Boltzmann constant was assigned an exact value in 2019. Massimiliano Malgieri and Pasquale Onorato explain what this story teaches us.