A secure approach to determining the position of an entity can enable schemes such as position-based authorization for transactions and tracking of high-value targets. However, classical methods are incapable of providing secure position verification in the untrusted-prover case, meaning that a prover can mislead verifiers about its actual position. Here we propose and experimentally realize a secure position verification protocol that combines quantum optics and relativity within an information-theoretic framework. Using phase-randomized weak coherent states, two verifiers separated by 2 km securely verify the prover’s position with an accuracy better than 75 m. These results establish secure position-based authentication as a practical possibility, paving the way for applications in financial transactions, disaster response and authenticated secure communications. By combining quantum and relativistic physics, it is possible to verify someone’s position remotely without needing to trust them. Such a position verification protocol has now been introduced and demonstrated with a quantum optics experiment.
Altermagnetism, characterized by compensated antiparallel spin order accompanied by finite spin splitting, bridges the properties of ferromagnets and antiferromagnets and holds promise for next-generation spintronic applications. Theoretical studies suggest that twisting van der Waals layers can induce altermagnetic states by tuning interlayer symmetry, thereby expanding the family of magnetic quantum materials. However, direct experimental observation of altermagnetism in these systems has not been achieved. Here we demonstrate altermagnetism in orthogonally twisted CrPS4/CrPS4 homostructures using magneto-optical spectroscopy. This structure exhibits a ferromagnetic-like magnetic-field dependence of the degree of circular polarization. Furthermore, a pronounced Zeeman splitting—absent in either ferromagnetic or antiferromagnetic CrPS4—emerges in the twisted configuration, indicating a distinct magnetic ground state. First-principles calculations reveal large spin-split bands in an antiferromagnetic configuration, confirming the realization of altermagnetism in twisted CrPS4. Polarized Raman spectroscopy further identifies interlayer-coupling-induced phonon-mode splitting unique to the altermagnetic state. These findings provide experimental evidence of altermagnetism in a twisted van der Waals material. Altermagnetic states hold promise for spintronic applications but are yet to be observed in twisted van der Waals materials. Now an orthogonally twisted CrPS4 homostructure is shown to exhibit signatures of altermagnetism.
Synthesis dependence is one of the biggest challenges faced by the field of quantum materials. Current synthesis methods introduce sample-to-sample variations that are poorly understood and difficult to control. This, in turn, leads to unreliable and unreproducible quantum materials and a lack of consensus across the community on their properties of interest. Here we highlight several examples of this synthesis dependence and propose steps that could overcome its challenges to deliver more reliable, reproducible and ultimately useful quantum materials. Interesting results in quantum materials often suffer from substantial inconsistencies between samples. This Perspective advocates for more careful study of synthesis dependence to realize the full potential of quantum materials science.
Light-dressed materials offer a route to generating electronic properties that differ from those of materials at equilibrium. The resulting band structures can host distinct quantum and topological phenomena. So far, optical control of charge within a light-dressed band structure has remained elusive. Here we demonstrate optical control of electrons in light-dressed graphene. By focusing circularly polarized femtosecond laser pulses at 1,550 nm on monolayer graphene, we generate a Floquet topological insulator. With a phase-locked second-harmonic field, we dynamically control electrons in this state, a technique we call harmonic Floquet spectroscopy. We observe photocurrent circular dichroism, an all-optical anomalous Hall effect and valley-polarized currents. The photocurrents show strong subcycle phase sensitivity, suggesting a route to ultrafast control in topological electronics, spectroscopy and attosecond physics in quantum materials. Driving a solid with light can create a topological insulator, but controlling its electrons has remained elusive. Optical control of electrons in a Floquet topological insulator has now been achieved in light-dressed graphene.
Carbon’s abundance, strong covalent bonding and relevance to inertial confinement fusion and planetary science have motivated extensive investigation of its phase diagram at terapascal pressures. However, the melting curve and the existence of phases beyond diamond remain uncertain. Here we resolve the discrepancy between experiments and theoretical simulations of the melting temperature of diamond and show that the diamond structure persists up to 1 TPa. This contradicts a previous report of a transition to the BC8 phase, which density functional theory predicts to be the thermodynamically stable phase of carbon above pressures around 1 TPa. We combine optical velocimetry, pyrometry and X-ray diffraction to probe microcrystalline diamond under nanosecond shock compression. Shock temperature and reflectivity measurements reveal changes in thermodynamic and optical properties, along with a decrease in X-ray diffraction intensity. These results provide evidence for shock-induced melting with a slight decrease in melting temperature with increasing pressure near 7,300 K. Our work delivers atomic-scale benchmarks for quantum simulations of condensed matter at extreme conditions, with implications for planetary interiors. Our improved understanding of diamond melting might also be relevant for achieving higher energy gain in laser-driven nuclear fusion. The location of the melting curve of diamond is unclear. Now, this is illuminated with shock compression experiments that provide strong evidence for shock-induced melting.
Wigner crystals—lattices made purely of electrons—provide a platform for studying correlation-driven quantum phase transitions. Despite extensive research, accessing the internal dynamics of Wigner crystals has remained challenging, with most experiments probing only static order or collective motion. Here we demonstrate optical probing and the manipulation of zero-field Wigner crystals and elucidate their static and dynamic properties in the frequency domain. We observe optical resonances that we identify as Wigner polarons—quasiparticles formed when the electron lattice is locally distorted by exciton–Wigner crystal coupling. We further achieve all-optical control of spins in the Wigner crystal, thereby directly probing valley-dependent Wigner polaron scattering well above the magnetic ordering temperature and in the absence of any external magnetic field. Finally, we show optical melting of the Wigner crystal and observe different responses of the umklapp (static) and Wigner polaron (dynamic) resonances to optical excitation. Our results provide an avenue for understanding electron dynamics and achieving ultrafast optical control of interaction-driven quantum phase transitions in strongly correlated electron systems. Wigner crystals have been observed in 2D semiconductors, but their internal dynamics have been largely inaccessible. Now this is demonstrated in a monolayer semiconductor.
Owing to its exceptional characteristics, diamond finds many applications in metrology. Anita Chandran introduces us to the glittering world of natural and synthetic diamonds.
Quantifying particle interactions is central to understanding and controlling collective dynamics in particle-based devices such as those comprising skyrmion ensembles. Here we directly visualize, in real time, the nanosecond current-driven dynamics of an antiferromagnetic skyrmion lattice. By tuning the spin–orbit torque relative to local pinning, we identify two regimes: an incoherent flow, where mobile skyrmions are driven toward pinned neighbours undergoing compression followed by a recoil, and a coherent flow regime, where the lattice translates uniformly. We use an inverse analysis method based on the Thiele equation to extract an exponentially decaying antiferromagnetic skyrmion interaction potential, which is in agreement with simulation results. At higher current densities, the lattice exhibits coherent motion free from detectable Hall and inertial effects or dynamical deformation, and this enables robust ultrafast operation. These findings establish a quantitative framework for antiferromagnetic skyrmion interactions and demonstrate deterministic control of their collective dynamics, even in the incoherent flow regime, thereby providing potential applications for multiskyrmion spintronic devices. Understanding the time-resolved dynamics of antiferromagnetic skyrmion interactions remains a challenge, limiting control over their collective behaviour. Now their ultrafast dynamics is visualized in real time in thin-film multilayers.
Faithful chromosome segregation during mitosis relies on the formation of compact, individualized chromosomes that withstand drag and spindle-generated forces. Structural failure of mitotic chromosomes under force can disrupt the distribution of genetic material to daughter cells, causing aneuploidy or cancer. The overall mechanical properties of mitotic chromosomes have been suggested to arise from their structural heterogeneity. The magnitude and scale of this heterogeneity have not been measured, leaving its impact on chromosome mechanics unresolved. Here we show that chromosomes are highly mechanically heterogeneous: within one chromosome, the local stiffness can vary by up to two orders of magnitude. This extreme mechanical heterogeneity is exemplified by the centromere, which is an order of magnitude softer than the whole chromosome. These results demonstrate how the mechanical complexity of mitotic chromosomes gives rise to their emergent nonlinear mechanical behaviour, distinct from the polymer properties of their constituents. More broadly, we discuss how structural heterogeneity can shape the nonlinear responses of composite materials, with implications for both understanding biological assemblies and designing new synthetic materials. Analysis of the mechanical properties of mitotic chromosomes is key for understanding the robustness of chromosomes during cell division. It is now shown that chromosomes are highly mechanically heterogeneous.
The theory of generalized symmetries has recently clarified how twisted sectors resolve the Callan–Rubakov paradox, where scattering of a charged particle by a magnetic monopole appeared to violate conservation laws. Here we study a more general setting of wavepackets that propagate across topological interfaces in quantum spin systems exhibiting non-invertible symmetries and across duality defects coupling dual theories. In these scenarios, we find that the transmission is always perfect and a particle traversing the interface is converted into a non-local string-like excitation. We give a systematic way of constructing such a defect by identifying its Hilbert space with the virtual bond dimension of the matrix product operator representing defect lines. Our work provides a precise characterization of topological interfaces in perfect transmission phenomena and yields a lattice analogue of the solution to the monopole paradox in quantum field theory. Dualities between different models are an important tool in theoretical many-body physics. Here a constructive recipe is given for topological interfaces between dual models that are transparent to wavepackets but alter their properties.
Non-Hermitian systems trace braid-like eigenvalue paths that are difficult to observe directly. Coupled chip-scale lasers now reveal braided spectra, enabling real-time visualization of non-Hermitian topology.
It is unclear whether crystalline disorder can suppress angular momentum transport. Now, a study reveals the disorder resilience of such transport and uncovers distinct orbital relaxation processes across a wide range of disordered thin films.
Altermagnetism is a magnetic phase that combines zero net magnetization with time-reversal-symmetry breaking and momentum-dependent spin splitting, but it has so far been confined to fermionic systems. Here we report a photonic platform capturing the symmetry features of altermagnetism. Using a magnetophotonic crystal with staggered magnetic bias and controlled structural variation, we observe momentum-dependent polarization splitting, spin–momentum locking and vanishing net magnetization in the photonic band structure. By solving Maxwell’s equations, we show that the momentum-dependent splitting is symmetry governed, rather than a consequence of the momentum-independent gyrotropic effect. These results demonstrate a photonic analogue of altermagnetic behaviour and provide a route towards spin-functional photonic devices without net magnetization. Altermagnetism has been experimentally demonstrated in fermionic systems, but not yet in photonic systems. Now it is observed in a magnetophotonic crystal.
