We study how simple eukaryotic organisms make decisions in response to competing stimuli in the context of phototaxis by the unicellular alga Chlamydomonas reinhardtii. While negatively phototactic cells swim directly away from a collimated light beam, when presented with two beams of adjustable intersection angle and intensities, we find that cells swim in a direction given by an intensity-weighted average of the two light propagation vectors. This geometrical law is a fixed point of an adaptive model of phototaxis and minimizes the average light intensity falling on the anterior pole of the cell. At large angular separations, subpopulations of cells swim away from one source or the other, or along the direction of the geometrical law, with some cells stochastically switching between the three directions. This behavior is shown to arise from a population-level distribution of photoreceptor locations that breaks front-back symmetry of photoreception.

In the early days of laser spectroscopy, Letokhov and Chebotayev proposed a scheme for measuring narrow spectral lines where the resolution is not restricted to Doppler effects because the molecules are entrained in a standing-wave light field. Now, such one-dimensional trapping in the intensity maxima of an intracavity field, slightly detuned from resonance, is experimentally demonstrated in the measurement of the very weak S(0) (2-0) quadrupole overtone transition in ${\mathrm{H}}_2$ at 1189 nm. The trapping manifests as an extremely narrow absorption feature at the predicted zero-recoil position, a 70 kHz shift from the blue-recoil component observed in Lamb-dip spectroscopy. A quantitative analysis of the saturation and trapping conditions supports the findings.

NbRe is a noncentrosymmetric superconductor that has been proposed as a candidate for intrinsic spin-triplet pairing. However, a conclusive demonstration of triplet pairing in NbRe is yet to be found. To probe the presence of spin-triplet Cooper pairs, we fabricated $\mathrm{Py}/\mathrm{NbRe}/\mathrm{Py}$ trilayers capped with an antiferromagnetic layer. Magnetic and electrical measurements reveal an inverse spin-valve effect, which could indicate equal-spin-triplet superconductivity. The minimal sample structure and the lack of ad hoc engineered interfaces clearly associate our observation to intrinsic triplet correlations of NbRe. The availability of NbRe in thin-film form and the simplicity of the heterostructure highlight its potential as a scalable platform for superconducting spintronics.

The violation of Leggett-Garg inequality (LGI) indicates general temporal correlations in quantum systems that cannot be explained classically. Under unitary dynamics and projective measurements, the violation of LGI is restricted up to the temporal Tsirelson’s bound (TTB). Here, we consider superposition of unitary time evolutions and find them to produce an enhancement in the violation of LGI beyond the TTB, growing monotonically with increasing superposition. We experimentally realize superposition of unitaries in NMR systems and demonstrate this enhanced violation. In the presence of noise, such superposition of unitaries remarkably extend the time of LGI violation, showcasing improved robustness against decoherence. This opens up possibilities of employing such nontrivial dynamical maps for robust quantum control, along with provoking research on characterizing correlations in general sequential measurement scenarios.

Small superconducting islands can exhibit charge quantization, where Coulomb interactions compete with Cooper pairing. Using scanning tunneling spectroscopy, we probe this interplay by measuring the charging energy ($E_C$) and the pairing energy ($\mathrm{\Delta }$) of individual Pb nanoislands. Below a critical island size, where $E_C>\mathrm{\Delta }$, we observe a crossover between even and odd parity ground states. By applying controlled voltage pulses, we continuously tune the island’s electrostatic potential and map the full charge-parity landscape. These results demonstrate tunable superconducting ground states, offering a potential platform for qubit design and control.

Organic semiconductors show complex phenomena due to their high energetic disorder. A striking example is the possibility of an increased effective temperature $T_{\mathrm{eff}}$ of the charge carrier distribution relative to the lattice temperature, which results from the slow charge carrier relaxation after excitation, either by high electric field or photon absorption. The increased effective temperature has been linked to conductivity enhancements and performance increases in actual devices, but a direct observation has been lacking. Here, we utilize nanoscopic tree-terminal devices to measure the Seebeck voltage arising in a doped organic polymer semiconductor due to a field-driven enhancement of the effective electronic temperature, providing direct proof of the existence of $T_{\mathrm{eff}}$. The results agree quantitatively with numerical predictions by a kinetic Monte Carlo model. The findings not only provide fundamental understanding but also indicate an avenue toward low-loss thermoelectric devices.

Recently, unconventional spin-orbit torques (SOTs) with tunable spin generation have opened new pathways for designing novel magnetization control for cutting-edge spintronics innovations. A leading research thrust is to develop field-free deterministic magnetization switching for implementing scalable and energy favorable magnetic recording and storage, which have been demonstrated in conventional ferromagnetic and antiferromagnetic material systems. Here, we extend this advanced magnetization control strategy to chiral antiferromagnet ${\mathrm{Mn}}_3\mathrm{Sn}$ using spin currents with out-of-plane canted polarization generated from low-symmetry van der Waals (vdW) material ${\mathrm{WTe}}_2$. Numerical calculations suggest that dampinglike SOT of spins injected perpendicular to the kagome plane of ${\mathrm{Mn}}_3\mathrm{Sn}$ serves as a driving force to rotate the chiral magnetic order, while the fieldlike SOT of spin currents with polarization parallel to the kagome plane provides the bipolar deterministicity to the magnetic switching in the absence of an external magnetic field. We further introduce scanning quantum microscopy to visualize nanoscale evolutions of ${\mathrm{Mn}}_3\mathrm{Sn}$ magnetic domains during the field-free switching process, corroborating the exceptionally large magnetic switching ratio up to 90%. Our results highlight the opportunities provided by hybrid SOT material platforms consisting of noncollinear antiferromagnets and low-symmetry vdW spin source materials for developing next-generation spintronic logic devices.

Quantum conductance effects start to appear as the size of electronic devices decreases and they are used in the next generation memristors and quantum calculations. Understanding the relationship between line width and resistance is crucial for developing quantized electronic devices. This Letter reports the development of an electromechanical testing device based on microelectromechanical systems integrated within a transmission electron microscope for in situ investigations at atomic resolution. The resistance changes of single crystalline gold (Au) wires, spanning from hundreds of nanometers down to several atoms are investigated. A transition in resistance from quasiballistic to ballistic transport states is uncovered. The experimental data fitted by calculation show that the ballistic transport limit for single crystal Au at room temperature is about 2.5 nm, beyond which the transmission probability experienced a rapid drop.

Optical tweezers are widely used as a highly sensitive tool to measure forces on micron-scale particles. One such application is the measurement of the electric charge of a particle, which can be done with high precision in liquids, air, or vacuum. We experimentally investigate how the trapping laser itself can electrically charge such a particle, in our case a $\sim 1\mathrm{\mu }\mathrm{m}$ ${\mathrm{SiO}}_2$ sphere in air. We model the charging mechanism as a two-photon process which reproduces the experimental data with high fidelity.

There are many exotic thermodynamic processes that are hard to study in nature. Here, we synthesize a structured environment to explore the extremes of thermodynamics. We present an engine running at extreme temperatures of above ten Megakelvin. Our underdamped engine is realised by electrically levitating and controlling a charged microparticle in vacuum. Giant fluctuations are observed in the engine’s heat exchange with the environment, while its efficiency shows stochastic events where more work is performed by the engine than heat consumed. Moreover, the nonuniformity of the synthetic environment leads to the particle experiencing position dependent diffusion, a critical phenomenon in microscale biological processes. We theoretically account for the effects of multiplicative noise and find excellent agreement with the observed behavior.

We present a search for light dark matter particles through their interactions with atomic electrons and nucleons, utilizing PandaX-4T data with an effective exposure of $1.04\mathrm{tonne}·\mathrm{year}$ for ionization-only data and $1.20\mathrm{tonne}·\mathrm{year}$ for paired data. Our analysis focuses on the energy range (efficiency $>0.01$) of approximately 0.33 to 3 keV for nuclear recoils and from 0.04 to 0.39 keV for electronic recoils. We establish the most stringent constraints on spin-independent dark matter-nucleon interactions within a mass range of $2.5–5.0\mathrm{GeV}/c^2$, spin-dependent neutron-only interactions within $1.0–5.6\mathrm{GeV}/c^2$, and spin-dependent proton-only interactions within $1.0–4.1\mathrm{GeV}/c^2$. Their corresponding limits at $3\mathrm{GeV}/c^2$ are $1.1\times {10}^{-43}$, $8.4\times {10}^{-40}$, and $2.8\times {10}^{-38}{\mathrm{cm}}^2$, respectively. Additionally, our results improve the upper limits on the dark matter-electron scattering cross section by a factor of 1.5 and 9.3 for heavy and light mediator scenarios, respectively, within $50\mathrm{MeV}/c^2$ to $10\mathrm{GeV}/c^2$, compared with previous best results. The improved limits reach $1.5\times {10}^{-41}$ and $5.6\times {10}^{-37}{\mathrm{cm}}^2$ at $200\mathrm{MeV}/c^2$ for the heavy and light mediators, respectively.

When embedded in superfluid helium nanodroplets, the dopant molecule exhibits either localization or delocalization behaviors that are critically determined by the spatial spread of its wave function, which in turn are influenced by the confining potential of the nanodroplets. Here, we examine the spatial extent of a molecule’s wave function with respect to the size of the nanodroplet by diagnosing the angular nodal structures in the photoelectron momentum distributions (PMDs). We find that, for the lightest ${\mathrm{H}}_2$ molecules or heavier ${\mathrm{D}}_2$ and ${\mathrm{O}}_2$ molecules, with extents of wave function distributions comparable to or smaller than the nanodroplet size, the emitted electrons undergo either minimal or significant scattering with the liquid helium surroundings, leading to either preserved or blurred nodal structures in the PMDs. These observations reveal the underlying delocalization or localization of a molecule within the nanodroplet, which is governed by its wave functions as determined by the confining potential of the droplet. Our findings provide insight into the quantum solvation dynamics of light impurities in nanoscale and confined systems.

The concept of flux in quantum physics is connected to many intriguing phenomena such as the Aharonov-Bohm effect and Hofstadter butterfly. Particularly, flux in lattices with certain symmetries gives rise to many unprecedented phases of matter. Here, we report the experimental realization of two-dimensional photonic crystals featuring diverse synthetic $\pi$-flux patterns, achieved through harnessing the higher-orbital degree of freedom within confined-Mie-resonance photonic crystals. As a proof of concept, we fabricate two types of $\pi$-flux photonic crystals, and show that novel topological phases can emerge with peculiar optical effects, including a topological edge state with $4\pi$-period phase evolution, as well as two pairs of topological states which are localized at opposite boundaries but related by a nonlocal twist. These signatures characterize unambiguously a photonic Möbius insulator [an insulator with topological edge states with a $4\pi$-periodic sideband junction (like a Möbius ring)] and a momentum-space-nonsymmorphic symmetry characterized insulator, which remain experimentally unexplored to date. Our Letter opens the frontiers to explore the underlying physics between synthetic $\pi$-flux and photonic crystals.

We investigated ultrafast defect-lattice dynamics in diamond using the ${\mathrm{N}}_{\mathrm{s}}:{\mathrm{H}\text{−}\mathrm{C}}^0$ defect, an analog of bond-centered hydrogen in semiconductors. Combining synthesis, ultrafast vibrational spectroscopy, and ab initio calculations, we show that excitation of the defect’s stretch mode leads to the generation of localized phonons and the formation of a hot ground state, where the interatomic potential is transiently modified. Our results reveal unexpected nonequilibrium phonon effects despite diamond’s exceptionally high thermal conductivity, with implications for quantum defect engineering.

While hydrodynamic coupling has long been considered essential for synchronization of eukaryotic flagella, recent experiments on the unicellular biflagellate model organism Chlamydomonas demonstrate that -at the single cell level- intracellular mechanical coupling is necessary for coordination. It is therefore unclear what role, if any, hydrodynamic forces actually play in the synchronization of multiple flagella within individual cells, arguably the building block of large scale coordination. Here we address this question experimentally by transiently blocking hydrodynamic coupling between the two flagella of single Chlamydomonas. Our results reveal that in wild type cells intracellularly mediated forces are necessary and sufficient for flagellar synchronization, with hydrodynamic coupling causing minimal changes in flagellar dynamics. However, fluid-mediated ciliary coupling is responsible for the extended periods of anti-phase synchronization observed in a mutant with weaker intracellular coupling. At the single-cell level, therefore, flagellar coordination depends on a subtle balance between intracellular and extracellular forces.

While the spin-ice state of bulk pyrochlores such as ${\mathrm{Dy}}_2{\text{Ti}}_2{\mathrm{O}}_7$ and ${\mathrm{Ho}}_2{\text{Ti}}_2{\mathrm{O}}_7$ has been extensively studied in the past several decades due to its unique degenerate ground state and emergent monopole excitation, whether it survives in the thin-film form remains a mystery. The limited volume of the thin-film sample makes it challenging to study the intrinsic magnetic properties. Here, we synthesized 18-nm-thick ${\mathrm{Dy}}_2{\text{Ti}}_2{\mathrm{O}}_7$ thin film on yttria-stabilized zirconia with $9.5\mathrm{mol}\%{\mathrm{Y}}_2{\mathrm{O}}_3$ substrate and capped it by a thin conductive ${\mathrm{Bi}}_2{\text{Ir}}_2{\mathrm{O}}_7$ layer and performed the proximitized magnetoresistance measurements. Our Letter found that the ice-rule-breaking phase transition survives but with a modified effective nearest-neighbor interaction ($J_{\mathrm{eff}}=1.054\mathrm{K}$) and distorted Ising spin axes ($\epsilon =+0.051$) compared to the bulk crystal. The results are supported by the simultaneously measured capacitive torque magnetometry. Our Letter demonstrates that proximitized transport is an effective tool for thin films of insulating frustrated magnets.

Altermagnets are a novel class of magnetic materials with cutting-edge advantages. Identifying altermagnets, i.e., exploring their distinguishing fingerprints, is vital but challenging. The as-reported spontaneous anomalous Hall effect is not universally present in all altermagnets due to magnetic symmetry constraints, and the second-order nonlinear Hall effect is prohibited by spatial-inversion symmetry. Here, we report the experimental discovery of a third-order nonlinear Hall effect (TNHE) in ${\text{RuO}}_2$ thin films. TNHE emerges when current is applied along [110] or $[\overline{1}10]$ crystal direction for ${\text{RuO}}_2(001)$, as the second-order currents induce a magnetization by breaking orthogonal mirror and rotation symmetries of this altermagnet. These symmetry-breaking conditions also enforce a twofold angular dependence of TNHE concerning current direction in the ${\text{RuO}}_2(001)$ plane. Moreover, temperature-dependent measurements and scaling law analysis reveal that TNHE is governed primarily by the third-order skew scattering mechanism. Our findings establish TNHE as a transport fingerprint of altermagnet ${\text{RuO}}_2$, which can be generalized to other altermagnets such as $d$-wave ${\mathrm{V}}_2{\mathrm{X}}_2\mathrm{O}$ ($\mathrm{X}=\text{Se}$ or Te) and $g$-wave MnTe and CrSb.

Conformal transformation is a powerful paradigm for designing isotropic metamaterials with significant practical value. However, conventional conformal transformation faces challenges in achieving precise multiphysics control, specifically for the concurrent regulation of thermal and electromagnetic fields. This difficulty arises because the interface matching mechanisms for dissipative thermal fields and nondissipative electromagnetic fields are fundamentally different. To overcome these challenges, we propose a common design paradigm for multiphysics-applicable interface matching, based on rescaled Schwarz-Christoffel transformation (RSCT). This framework leverages the Schwarz-Christoffel transformation—a conformal map between polygonal domains that intrinsically directs energy flow—and integrates it with rescaling techniques that enable the redistribution of energy flow density. By simultaneously controlling energy flow and energy flow density, two key quantities that can be manipulated in both thermal and electromagnetic fields, RSCT establishes a general platform for perfect interface matching using solely isotropic media. Employing RSCT, we design and experimentally validate three energy-flow regulators: expanders, guiders, and cloaks. Furthermore, the inherent capability of RSCT to form devices of arbitrary polygonal shapes makes it highly compatible with the layout of integrated circuits, holding great promise for coordinated signal and heat management in such systems.

We experimentally realize a quantum clock by using a charge sensor to count charges tunneling through a double quantum dot (DQD). Individual tunneling events are used as the clock’s ticks. We quantify the clock’s precision while measuring the power dissipated by the DQD and, separately, the charge sensor in both direct-current and radio-frequency readout modes. This allows us to probe the thermodynamic cost of creating ticks microscopically and recording them macroscopically. Our experiment is the first to explore the interplay between the entropy produced by a microscopic clockwork and its macroscopic measurement apparatus. We show that the latter contribution not only dwarfs the former but also unlocks greatly increased precision, because the measurement record can be exploited to optimally estimate time even when the DQD is at equilibrium. Our results suggest that the entropy produced by the amplification and measurement of a clock’s ticks, which has often been ignored in the literature, is the most important and fundamental thermodynamic cost of timekeeping at the quantum scale.

Creating and manipulating anyons and symmetry defects in topological phases, especially those with a non-Abelian character, constitutes a primitive for topological quantum computation. We provide a physical protocol for implementing the ribbon operators of non-Abelian anyons and symmetry defects. We utilize dualities, in particular, the Kramers-Wannier or gauging map, which have previously been used to construct topologically ordered ground states by relating them to simpler states. In this Letter, ribbon operators are implemented by applying a gauging procedure to a lower-dimensional region of such states. This protocol uses sequential unitary circuits or, in certain cases, constant-depth adaptive circuits. We showcase this for anyons and defects in the ${\mathbb{Z}}_3$ toric code and $S_3$ quantum double. The general applicability of our method is demonstrated by deriving unitary expressions for ribbon operators of various (twisted) quantum doubles.