For over 100 years, two theories have shaped our understanding of the universe: quantum mechanics and Einstein’s general relativity. One explains the tiny world of particles; the other describes gravity and the fabric of space. But despite their individual success, bringing them together has remained one of science’s greatest unsolved problems.

Now, a team of researchers at University College London has introduced a bold new idea. Rather than tweaking Einstein’s theory to fit into quantum rules, they suggest flipping the script. Their model, called a “postquantum theory of classical gravity,” aims to rethink the deep link between gravity and the quantum world.

Quantum mechanics thrives on probabilities, uncertainty, and the strange behavior of subatomic particles. It’s helped explain the structure of atoms and power modern technology. Meanwhile, general relativity offers a grand view of the universe, where planets and stars bend spacetime and create what we feel as gravity.

A concept based on an exotic effect in periodic structures may be useful for developing future photonic devices.

A new way to marshal light within optical devices has been demonstrated experimentally by researchers in China. They have been able to induce light to organize itself into specific patterns of pulses as it circulates within a pair of optical fiber loops using a version of a phenomenon—called the non-Hermitian skin effect (NHSE)—that has been predicted but not observed previously [1]. The effect could be used to control light signals in photonic devices such as switches and routers.

In the standard theory for electron behavior in a metallic crystal, the periodic atomic structure leads to so-called Bloch waves—electron quantum states that spread across the entire crystal. But in recent years, theorists have found surprising results for a scenario in which one assumes that a particle such as an electron hops between neighboring sites in a periodic lattice asymmetrically—say, rightward hopping is more probable than leftward hopping. The particle’s quantum states become localized at the edge or surface of the lattice rather than spreading across it. This localization is the NHSE.

Embezzlement of entanglement is an exotic phenomenon in quantum information science, describing the possibility of extracting entanglement from a resource system without changing its quantum state. In this context, the resource systems play the role of a catalyst, enabling a state transition that would otherwise be impossible, without being consumed in the process. For embezzlement of entanglement to be possible, the resource state needs to be highly entangled.

The term “universal embezzler” refers to the idea of a bipartite quantum system where every state is sufficiently entangled to make embezzlement possible. So far, it seemed highly questionable that physical systems exhibiting such strong entanglement properties could exist in the first place.

Yet researchers at Leibniz University Hannover have now shown that universal embezzlement emerges in all critical fermion chains, meaning one-dimensional fermion systems at quantum phase transitions. While their paper, published in Nature Physics, is merely theoretical, it could open new possibilities for the study of many-body physics and for the development of quantum technologies.