For localization of a sound source, animals and humans process the microsecond interaural time differences of arriving sound waves. How nervous systems, consisting of elements with time constants of about and more than 1 ms, can reach such high precision is still an open question. In this Letter we present a hypothesis and show theoretical and computational evidence that a rather large population of slowly integrating neurons with inhibitory and excitatory inputs ($EI$ neurons) can detect minute temporal disparities in input signals which are significantly less than any time constant in the system.

We report on ultrafast optical experiments in which femtosecond midinfrared radiation is used to excite the lattice of complex oxide heterostructures. By tuning the excitation energy to a vibrational mode of the substrate, a long-lived five-order-of-magnitude increase of the electrical conductivity of ${\mathrm{NdNiO}}_3$ epitaxial thin films is observed as a structural distortion propagates across the interface. Vibrational excitation, extended here to a wide class of heterostructures and interfaces, may be conducive to new strategies for electronic phase control at THz repetition rates.

Metallic nanostructures support extreme localization and enhancement of optical fields via surface-plasmon (SP) resonances. Although SP are associated with giant enhancements of nonlinear phenomena such as second-harmonic generation (SHG), the role of SP in the process, whether as a field-enhancing catalyst or as a quasiparticle converted in the interaction, has remained experimentally elusive. We demonstrate how $k$-space spectroscopy can distinguish between the plasmonic and photonic SHG processes that occur in a metal nanofilm when it is optically driven via the Kretschmann geometry. The results revealed a nonlinear interaction where two SP annihilate to create a second-harmonic photon. This knowledge has implications for realizing the inverse process, plasmonic parametric down-conversion, which could act as a coherent source of entangled SP pairs.

We introduce the idea of actually cooling quantum systems by means of incoherent thermal light, hence giving rise to a counterintuitive mechanism of “cooling by heating.” In this effect, the mere incoherent occupation of a quantum mechanical mode serves as a trigger to enhance the coupling between other modes. This notion of effectively rendering states more coherent by driving with incoherent thermal quantum noise is applied here to the optomechanical setting, where this effect occurs most naturally. We discuss two ways of describing this situation, one of them making use of stochastic sampling of Gaussian quantum states with respect to stationary classical stochastic processes. The potential of experimentally demonstrating this counterintuitive effect in optomechanical systems with present technology is sketched.

We propose a new mechanism for refrigeration powered by photons. We identify the strong coupling regime for which maximum efficiency is achieved. In this case, the cooling flux is proportional to $T$ in the low temperature limit $T\to 0$.

We propose an experiment where a photon is first cloned by stimulated parametric down-conversion, making many (imperfect) copies, and then the cloning transformation is inverted, regenerating the original photon while destroying the copies. Focusing on the case where the initial photon is entangled with another photon, we study the conditions under which entanglement can be proven in the final state. The proposed experiment would provide a clear demonstration that quantum information is preserved in quantum cloning. It would furthermore allow a definitive experimental proof for micro-macro entanglement in the intermediate multiphoton state, which is still an outstanding challenge. Finally, it might provide a quantum detection technique for small differences in transmission (e.g., in biological samples), whose sensitivity scales better with the number of photons used than a classical transmission measurement.

The behavior of any physical system is governed by its underlying dynamical equations. Much of physics is concerned with discovering these dynamical equations and understanding their consequences. In this Letter, we show that, remarkably, identifying the underlying dynamical equation from any amount of experimental data, however precise, is a provably computationally hard problem (it is NP hard), both for classical and quantum mechanical systems. As a by-product of this work, we give complexity-theoretic answers to both the quantum and classical embedding problems, two long-standing open problems in mathematics (the classical problem, in particular, dating back over 70 years).

The 7.6(5) eV nuclear magnetic-dipole transition in a single ${}^{229}\mathrm{Th}^{3+}$ ion may provide the foundation for an optical clock of superb accuracy. A virtual clock transition composed of stretched states within the $5F_{5/2}$ electronic ground level of both nuclear ground and isomeric manifolds is proposed. It is shown to offer unprecedented systematic shift suppression, allowing for clock performance with a total fractional inaccuracy approaching $1\times {10}^{-19}$.

During the last decade of network research focusing on structural and dynamical properties of networks, the role of network users has been more or less underestimated from the bird’s-eye view of global perspective. In this era of global positioning system equipped smartphones, however, a user’s ability to access local geometric information and find efficient pathways on networks plays a crucial role, rather than the globally optimal pathways. We present a simple greedy spatial navigation strategy as a probe to explore spatial networks. These greedy navigators use directional information in every move they take, without being trapped in a dead end based on their memory about previous routes. We suggest that the centralities measures have to be modified to incorporate the navigators’ behavior, and present the intriguing effect of navigators’ greediness where removing some edges may actually enhance the routing efficiency, which is reminiscent of Braess’s paradox. In addition, using samples of road structures in large cities around the world, it is shown that the navigability measure we define reflects unique structural properties, which are not easy to predict from other topological characteristics. In this respect, we believe that our routing scheme significantly moves the routing problem on networks one step closer to reality, incorporating the inevitable incompleteness of navigators’ information.

A cavity optomechanical magnetometer is demonstrated. The magnetic-field-induced expansion of a magnetostrictive material is resonantly transduced onto the physical structure of a highly compliant optical microresonator and read out optically with ultrahigh sensitivity. A peak magnetic field sensitivity of $400\mathrm{nT}{\mathrm{Hz}}^{-1/2}$ is achieved, with theoretical modeling predicting the possibility of sensitivities below $1\mathrm{pT}{\mathrm{Hz}}^{-1/2}$. This chip-based magnetometer combines high sensitivity and large dynamic range with small size and room temperature operation.

We report magnetic, dielectric, and magnetodielectric responses of the pure monoclinic bulk phase of partially disordered ${\mathrm{La}}_2{\mathrm{NiMnO}}_6$, exhibiting a spectrum of unusual properties and establish that this compound is an intrinsically multiglass system with a large magnetodielectric coupling (8%–20%) over a wide range of temperatures (150–300 K). Specifically, our results establish a unique way to obtain colossal magnetodielectricity, independent of any striction effects, by engineering the asymmetric hopping contribution to the dielectric constant via the tuning of the relative-spin orientations between neighboring magnetic ions in a transition-metal oxide system. We discuss the role of antisite (Ni-Mn) disorder in emergence of these unusual properties.

We show that by coiling up space using curled perforations, a two-dimensional acoustic metamaterial can be constructed to give a frequency dispersive spectrum of extreme constitutive parameters, including double negativity, a density near zero, and a large refractive index. Such an approach has band foldings at the effective medium regime without using local resonating subwavelength structures, while the principle can be easily generalized to three dimensions. Negative refraction with a double negative prism and tunneling with a density-near-zero metamaterial are numerically demonstrated.

The effect of increasing prepulse energy levels on the energy spectrum and coupling into forward-going electrons is evaluated in a cone-guided fast-ignition relevant geometry using cone-wire targets irradiated with a high intensity (${10}^{20}\mathrm{W}/{\mathrm{cm}}^2$) laser pulse. Hot electron temperature and flux are inferred from $K\alpha$ images and yields using hybrid particle-in-cell simulations. A two-temperature distribution of hot electrons was required to fit the full profile, with the ratio of energy in a higher energy (MeV) component increasing with a larger prepulse. As prepulse energies were increased from 8 mJ to 1 J, overall coupling from laser to all hot electrons entering the wire was found to fall from 8.4% to 2.5% while coupling into only the 1–3 MeV electrons dropped from 0.57% to 0.03%.

Lévy flights constitute a broad class of random walks that occur in many fields of research, from biology to economy and geophysics. The recent advent of Lévy glasses allows us to study Lévy flights—and the resultant superdiffusion—using light waves. This raises several questions about the influence of interference on superdiffusive transport. Superdiffusive structures have the extraordinary property that all points are connected via direct jumps, which is expected to have a strong impact on interference effects such as weak and strong localization. Here we report on the experimental observation of weak localization in Lévy glasses and compare our results with a recently developed theory for multiple scattering in superdiffusive media. Experimental results are in good agreement with theory and allow us to unveil the light propagation inside a finite-size superdiffusive system.

Publicly available clock correction data from the Global Positioning System was analyzed and used in combination with the results of terrestrial clock comparison experiments to confirm the local position invariance (LPI) of Planck’s constant within the context of general relativity. The results indicate that $h$ is invariant within a limit of $|{\beta }_h|<0.007$, where ${\beta }_h$ is a dimensionless parameter that represents the extent of LPI violation.

We report the first measurement of the parity-violating asymmetry $A_{\mathrm{PV}}$ in the elastic scattering of polarized electrons from ${}^{208}\mathrm{Pb}$. $A_{\mathrm{PV}}$ is sensitive to the radius of the neutron distribution ($R_n$). The result $A_{\mathrm{PV}}=0.656\pm 0.060(\mathrm{stat})\pm 0.014(\mathrm{syst})\mathrm{ppm}$ corresponds to a difference between the radii of the neutron and proton distributions $R_n-R_p={0.33}_{-0.18}^{+0.16}\mathrm{fm}$ and provides the first electroweak observation of the neutron skin which is expected in a heavy, neutron-rich nucleus.

Gas giants are believed to form by the accretion of hydrogen-helium gas around an initial protocore of rock and ice. The question of whether the rocky parts of the core dissolve into the fluid H-He layers following formation has significant implications for planetary structure and evolution. Here we use ab initio calculations to study rock solubility in fluid hydrogen, choosing MgO as a representative example of planetary rocky materials, and find MgO to be highly soluble in H for temperatures in excess of approximately 10 000 K, implying the potential for significant redistribution of rocky core material in Jupiter and larger exoplanets.

Sykes et al. [Proc. Natl. Acad. Sci. U.S.A. 102, 17907 (2005)] have reported how electrons injected from a scanning tunneling microscope modify the diffusion rates of $H$ buried beneath Pd(111). A key point in that experiment is the symmetry between positive and negative voltages for $H$ extraction, which is difficult to explain in view of the large asymmetry in Pd between the electron and hole densities of states. Combining concepts from the theory of ballistic electron microscopy and electron-phonon scattering we show that $H$ diffusion is driven by the $s$-band electrons only, which explains the observed symmetry.

Using computer simulations, we show that lipid membranes can mediate linear aggregation of spherical nanoparticles binding to it for a wide range of biologically relevant bending rigidities. This result is in net contrast with the isotropic aggregation of nanoparticles on fluid interfaces or the expected clustering of isotropic insertions in biological membranes. We present a phase diagram indicating where linear aggregation is expected and compute explicitly the free-energy barriers associated with linear and isotropic aggregation. Finally, we provide simple scaling arguments to explain this phenomenology.

We compute the universal generic corrections to the inflationary power spectrum due to unknown high-energy physics. We arrive at this result via a careful integrating out of massive fields in the “in-in” formalism yielding a consistent and predictive low-energy effective description in time-dependent backgrounds. We find that the power spectrum is universally modified at order $H/M$, where $H$ is the scale of inflation. This is qualitatively different from the universal corrections in time-independent backgrounds, and it suggests that such effects may be present in upcoming cosmological observations.