Nature Physics最新文献

Higher-order networks capture the many-body interactions present in complex systems, shedding light on the interplay between topology and dynamics. The theory of higher-order topological dynamics, which combines higher-order interactions with discrete topology and nonlinear dynamics, has the potential to enhance our understanding of complex systems, such as the brain and the climate, and to advance the development of next-generation AI algorithms. This theoretical framework, which goes beyond traditional node-centric descriptions, encodes the dynamics of a network through topological signals—variables assigned not only to nodes but also to edges, triangles and other higher-order cells. Recent findings show that topological signals lead to the emergence of distinct types of dynamical state and collective phenomena, including topological and Dirac synchronization, pattern formation and triadic percolation. These results offer insights into how topology shapes dynamics, how dynamics learns topology and how topology evolves dynamically. This Perspective primarily aims to guide physicists, mathematicians, computer scientists and network scientists through the emerging field of higher-order topological dynamics, while also outlining future research challenges.

Dissipation is an unavoidable feature of quantum systems, typically associated with decoherence and the modification of quantum correlations. In the study of strongly correlated quantum matter, we often have to overcome or suppress dissipation to uncover the underlying quantum phenomena. However, here we demonstrate that dissipation can serve as a probe for intrinsic correlations in quantum many-body systems. Applying tunable dissipation in ultracold atomic systems, we observe universal dissipative dynamics in strongly correlated one-dimensional quantum gases. Specifically, we find a universal stretched-exponential decay of the total particle number, where the stretched exponent measures the anomalous dimension of the spectral function—a parameter for characterizing strong quantum fluctuations. This approach offers a versatile framework for probing features of strongly correlated systems, including spin–charge separation and Fermi arcs in quantum materials.

Finding ground states of quantum many-body systems is known to be hard for both classical and quantum computers. Consequently, when a quantum system is cooled in a low-temperature thermal bath, the ground state cannot always be found efficiently. Instead, the system may become trapped in a local minimum of the energy. In this work, we study the problem of finding local minima in quantum systems under thermal perturbations. Although local minima are much easier to find than ground states, we show that finding a local minimum is hard on classical computers, even when the task is merely to output a single-qubit observable at any local minimum. By contrast, we prove that a quantum computer can always find a local minimum efficiently using a thermal gradient descent algorithm that mimics natural cooling processes. To establish the classical hardness of finding local minima, we construct a family of two-dimensional Hamiltonians such that any problem solvable by polynomial-time quantum algorithms can be reduced to finding local minima of these Hamiltonians. Therefore, cooling systems to local minima is universal for quantum computation and, assuming that quantum computation is more powerful than classical computation, finding local minima is classically hard but quantumly easy.

Ultrasensitive detection of the frequency, phase and amplitude of radiofrequency electric fields is crucial for applications in radio communication, cosmology, dark matter searches and high-fidelity qubit control. Quantum harmonic oscillator systems, especially trapped ions, offer high-sensitivity electric field sensing with nanometre spatial resolution but are typically restricted to narrow frequency ranges centred around the motional frequency of the trapped-ion oscillator or the frequency of an optical transition in the ion. Here we present a procedure that enables precise electric field detection over an expanded frequency range. Specifically, we use motional Raman transitions in a single trapped ion to achieve sensitivity across a frequency range over 800 times larger than previous approaches. We show that the method is compatible with both quantum amplification via squeezing and measurement in the Fock basis, allowing a demonstration of performance 3.4(2.0) dB below the standard quantum limit. The approach can be extended to other quantum harmonic oscillator systems, such as superconducting qubit–resonator systems.

Correction to: Nature Physics https://doi.org/10.1038/s41567-023-02089-1, published online 15 June 2023.

Correction to: Nature Physics https://doi.org/10.1038/s41567-024-02662-2, published online 11 October 2024.

The observation of superconductivity in La₃Ni₂O_7–δ under pressure, following the suppression of a high-temperature density wave state, has attracted considerable attention. The nature of this density wave order was not clearly identified. Here we probe the magnetic response of the zero-pressure phase of La₃Ni₂O_7–δ as hydrostatic pressure is applied, and find that the apparent single density wave transition at zero applied pressure splits into two. The comparison of our muon-spin rotation and relaxation experiments with dipole-field numerical analysis reveals the magnetic structure’s compatibility with a stripe-type arrangement of Ni moments, characterized by alternating lines of magnetic moments and non-magnetic stripes at ambient pressure. When pressure is applied, the magnetic ordering temperature increases, whereas the unidentified density wave transition temperature falls. Our findings reveal that the ground state of the La₃Ni₂O_7–δ system is characterized by the coexistence of two distinct orders—a magnetically ordered spin density wave and a lower-temperature ordering that is most probably a charge density wave—with a notable pressure-enhanced separation between them.

Flat-band moiré graphene systems are a quintessential platform for investigating correlated phases of matter. Various interaction-driven ground states have been proposed, but despite extensive experimental effort, there has been little direct evidence that distinguishes between various phases, in particular near the charge neutrality point. Here we probe the fine details of the density of states and the effects of Coulomb interactions in alternating-twist trilayer graphene by imaging the local thermodynamic quantum oscillations with a nanoscale scanning superconducting quantum interference device. We find that the charging self-energy due to occupied electronic states is most important in explaining the high-carrier-density physics. At half-filling of the conduction flat band, we observe ferromagnetic-driven symmetry breaking, suggesting that it is the most robust mechanism in the hierarchy of phase transitions. Near charge neutrality, where exchange energy dominates over charging self-energy, we find a nematic semimetal ground state, which is theoretically favoured over gapped states in the presence of heterostrain. In this semimetallic phase, the flat-band Dirac cones migrate towards the mini-Brillouin zone centre, spontaneously breaking the threefold rotational symmetry. Our low-field local quantum oscillation technique can be used to explore the ground states of many strongly interacting van der Waals systems.