Volume 17 Issue 3, March 2021

Muon colliders offer enormous potential for the exploration of the particle physics frontier but are challenging to realize. A new international collaboration is forming to make such a muon collider a reality.

The contact formalism describes short-range correlations, which play a crucial role in nuclear systems. Initially introduced for ultracold atoms, its generalization to the nuclear case was now validated by ab initio calculations.

Quantum computing combines great promise with daunting challenges — the road to devices that solve real-world problems is still long. Now, an implementation of a quantum algorithm maps the problems we want to solve to the devices we already have.

Measuring a quantum state often enough can leave you with a completely different phase of matter. Mix in competing measurements and you may find yourself with an entire phase diagram of dynamical quantum states and transitions.

A Cooper-pair box qubit is used to squeeze the energy of a heavy oscillating membrane towards a quantum energy eigenstate, bringing measurements of how mass and quantum mechanics interact one step closer.

Table-top superfluid experiments offer a way of bringing the physics of astrophysical black holes into the lab. But the presence of two event horizons in these superfluid black holes complicates matters — and makes them more interesting.

When molecular model systems, such as polycyclic aromatic hydrocarbons, are ionized by ultrashort extreme ultraviolet pulses, their relaxation path proceeds via electron–phonon scattering, linking molecules to typical solid-state matter behaviour.

Iridescent mother of pearl sports a complex structure that eludes standard imaging techniques. Now, a nanotomographic method provides high resolution 3D insight into the topological defects underpinning this composite material.

Effects of nucleon–nucleon correlations are studied with the generalized contact formalism and ab initio quantum Monte Carlo calculations. For nuclei from deuteron to ⁴⁰Ca, the many-body nuclear wave function is shown to factorize at short distances.

High-harmonic generation up to the seventh harmonic is observed from the intrinsic three-dimensional topological insulator BiSbTeSe₂. The parallel components of the even-order harmonics arise directly from the topological surface states.

Three-dimensional structures of vortex loops in a bulk micromagnet GdCo₂ have been observed using X-ray magnetic nanotomography. The cross-section of these loops consists of a vortex–antivortex pair stabilized by the dipolar interaction.

Strong quadratic coupling between the motion of a membrane and the energy states of a qubit enables the creation of a non-classical energy-squeezed state in the mechanical oscillator.

The size-dependent lifetimes observed in the ultrafast molecular relaxation dynamics of an entire class of polycyclic aromatic hydrocarbons can be explained by correlation bands and electron–phonon scattering, reminiscent of solid-state systems.

It is hoped that quantum computers may be faster than classical ones at solving optimization problems. Here the authors implement a quantum optimization algorithm over 23 qubits but find more limited performance when an optimization problem structure does not match the underlying hardware.

Finding expectation values is a key step in variational quantum algorithms that are hoped to provide a near-term quantum advantage. Bravyi et al. show that a classical approximation is possible when the quantum circuits are limited to constant depth.

Repeatedly measuring an array of qubits can create topologically distinct phases depending on which measurements are applied. Lavasani et al. show that critical behaviour can arise from the competition between different choices of measurements.

A general approach to derive direction-dependent complex refractive indices close to zero produces infinite families of time-reversible and infinite families of time-irreversible electromagnetic materials, without invoking the concept of topology.

A supersolid is a phase of matter featuring both crystalline order as a solid and global phase coherence as a superfluid. Now an experiment shows how this global phase coherence can be established across the system in a non-equilibrium process.

In an analogue black hole in an atomic Bose–Einstein condensate, spontaneous Hawking radiation is confirmed to be stationary and the time evolution of Hawking radiation is reported.

A spectroscopic study shows that vibrational pumping can be used to coherently control optical d–d transitions of electronic origin in the transition metal oxide system CuGeO₃.

Stacking a monolayer and bilayer of graphene, with a small twist angle between them, creates a tunable platform where the physics of both twisted bilayer graphene and twisted double bilayer graphene can be realized.

Strong electron–electron interactions create a charge-density wave that modifies the topological state of the Weyl semimetal (TaSe₄)₂I. This implies the possibility of experimentally simulating axion electrodynamics in a solid-state material.

Spin currents are generated from an antiferromagnet/heavy-metal heterostructure using optical excitation on picosecond timescales. This will have applications in antiferromagnetic spintronics.

In principle skyrmions are topologically protected, but the crystal lattice interferes with this protection so that they should be unstable to switching of their winding number. Here this process is understood via scanning tunnelling microscopy.

Certain bacteria cells respond to the stress of long-term exposure to antibiotics by changing their shape. Single-cell experiments and modelling cast this as a mechanical feedback strategy that makes bacteria more adaptive to surviving antibiotics.

Molluscs assemble layers of material in the shells around them with a high level of control. Here the authors observe the structural evolution of layer formation and propose a mechanism reminiscent of topological defect dynamics in liquid crystals.

Surface scientists love a good vacuum. The reason for this is captured by the work of Irving Langmuir and the little-known unit bearing his name, explains Daniel Payne.