Nature Physics最新文献

Strongly correlated quantum matter, such as interacting electron systems or interacting quantum fluids, exhibits properties that defy explanation in terms of linear fluctuations and free quasiparticles. In these systems, quantum fluctuations are large and generically display non-Gaussian statistics—a property captured only by inspecting high-order correlations, whose quantitative reconstruction presents a challenge for both experiments and theory. A prime example of correlated quantum matter is the strongly interacting Bose fluid, realized first in superfluid helium and, more recently, in ultracold atoms. Here, we experimentally study interacting Bose gases from the weakly to the strongly interacting regime through single-atom-resolved correlations in momentum space. We find that the Bogoliubov pairing among modes of opposite momenta, characteristic of the weakly interacting regime, is suppressed as interactions grow. This departure from the predictions of Bogoliubov theory marks the onset of the strongly correlated regime, as confirmed by numerical simulations that highlight the role of nonlinear quantum fluctuations in our system. Furthermore, our measurements reveal a non-zero four-operator cumulant at even stronger interactions, which is a direct signature of non-Gaussian correlations. These results shed light on the emergence and physical origin of non-Gaussian correlations in ensembles of interacting bosons.

Hydrodynamics is a successful framework for effectively describing the dynamics of complex many-body systems, ranging from subnuclear to cosmological scales. It applies coarse-grained assumptions about the microscopic constituents of a system to define macroscopic fluid cells, which are large compared to the interparticle spacing and mean free path. In high-energy heavy-ion collisions, hydrodynamic behaviour is inferred from the observation of elliptic flow, which is the elliptical deformation of the particle momentum distribution. Here we demonstrate the emergence of elliptic flow in a mesoscopic system with a few strongly interacting ultracold atoms. In our system, a hydrodynamic description is a priori not applicable, as all relevant length scales—the system size, the interparticle spacing and the mean free path—are comparable. The single-particle resolution and the deterministic control over the number of particles and interaction strength in our experiment allow us to explore the boundaries between a microscopic description and a hydrodynamic framework, and we show that elliptic flow appears as an interaction-driven effect. Our results demonstrate the emergence of collective behaviour in a regime where hydrodynamics is not usually applicable.

Active glasses are dense and disordered systems consisting of motile particles that display phenomenology observed in many biological systems. Here we investigate motility-driven annealing and fluidization in these systems and establish a correspondence between the yielding behaviour of glassy systems under active dynamics and their yielding under oscillatory shear. The yielded region of the phase diagram correlates with tissue fluidization, whereas the annealing region explains age-related maturation and stiffening. This suggests that some mechanical changes observed in ageing tissues can partially stem from processes analogous to enhanced ageing observed in active glasses. In addition to showing similar yielding diagrams, we strengthen the correspondence to oscillatory shear by demonstrating diverging time scales to steady states, the possibility of memory encoding and reading, and the importance of stress reversals in the annealing process in both cases. Finally, we study yielding in active solids and demonstrate that given the correct geometry, one can either suppress or promote brittle failure via shear band formation by tuning activity.

The topological θ-angle is central to several gauge theories in condensed-matter and high-energy physics. For example, it is responsible for the strong CP problem in quantum chromodynamics and can emerge in effective theories of electrodynamics in topological insulators. Although analogue quantum simulators potentially offer a venue for realizing and controlling the θ-angle, doing so has hitherto remained an outstanding challenge. Here, we describe the experimental realization of a tunable topological θ-angle in a Bose–Hubbard gauge-theory quantum simulator, which was implemented through a tilted superlattice potential that induces an effective background electric field. We demonstrate the emerging physics through the direct observation of the confinement–deconfinement transition of (1 + 1)-dimensional quantum electrodynamics. Using an atomic-precision quantum gas microscope, we distinguish between the confined and deconfined phases by monitoring the real-time evolution of particle–antiparticle pairs. Our work provides a step forward in the realization of topological terms on modern quantum simulators.

Correction to: Nature Physics https://doi.org/10.1038/s41567-023-02332-9, published online 17 January 2024.

The ability to control phonons in solids is key in many fields of quantum science, ranging from quantum information processing to sensing. Phonons often act as a source of noise and decoherence when solid-state quantum systems interact with the phonon bath of their host matrix. In this study, we demonstrate the ability to control the phononic local density of states of the host matrix using phononic crystals and measure its positive impact on single quantum systems. We design and fabricate diamond phononic crystals with features down to around 20 nm, resulting in a high-frequency complete phononic bandgap from 50 to 70 GHz. The engineered local density of states is probed using single silicon-vacancy colour centres embedded in the phononic crystals. We observe an 18-fold reduction in the phonon-induced orbital relaxation rate of the emitters compared to bulk, thereby demonstrating that the phononic crystal suppresses spontaneous single-phonon processes. Furthermore, we show that our approach can efficiently suppress single-phonon–emitter interactions up to 20 K, allowing the investigation of multi-phonon processes in the emitters. Our results represent an important step towards the realization of efficient phonon–emitter interfaces that can be used for quantum acoustodynamics and quantum phononic networks.

Quantum computing involves the preparation of entangled states across many qubits. This requires efficient preparation protocols that are stable to noise and gate imperfections. Here we demonstrate the generation of the simplest long-range order—Ising order—using a measurement-based protocol on 54 system qubits in the presence of coherent and incoherent errors. We implement a constant-depth preparation protocol that uses classical decoding of measurements to identify long-range order that is otherwise hidden by the randomness of quantum measurements. By experimentally tuning the error rates, we demonstrate the stability of this decoded long-range order in two spatial dimensions, up to a critical phase transition belonging to the unusual Nishimori universality class. Although in classical systems Nishimori physics requires fine-tuning multiple parameters, here it arises as a direct result of the Born rule for measurement probabilities. Our study demonstrates the emergent phenomena that can be explored on quantum processors beyond a hundred qubits.

Electronic spins can form long-range entangled phases of condensed matter named quantum spin liquids. They are expected to form in frustrated magnets that do not exhibit symmetry-breaking order down to zero temperature. Quantum spin ice is a theoretically well-established example described by an emergent quantum electrodynamics, with quasiparticle excitations behaving like photons and fractionally charged matter. However, in frustrated magnets it remains difficult to establish convincing experimental evidence for quantum spin liquid ground states and their fractional excitations. Here we study the time-dependent magnetic response of the candidate quantum spin ice material Ce₂Sn₂O₇. We find a gapped spectrum that features a threshold and peaks that match theories for pair production and propagation of fractional matter excitations strongly coupled to a background quantum electrodynamic field. The multiple peaks in our neutron spectroscopy data are a specific signature of the so-called π-flux phase of quantum spin ice, providing spectroscopic evidence for fractionalization in a three-dimensional quantum spin liquid.