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Time crystals are an eagerly sought phase of matter with broken time-translation symmetry. Quantum time crystals with discretely broken time-translation symmetry have been demonstrated in trapped ions, atoms and spins whereas continuously broken time-translation symmetry has been observed in an atomic condensate inside an optical cavity. Here we report that a classical metamaterial nanostructure, a two-dimensional array of plasmonic metamolecules supported on flexible nanowires, can be driven to a state possessing all of the key features of a continuous time crystal: continuous coherent illumination by light resonant with the metamolecules’ plasmonic mode triggers a spontaneous phase transition to a superradiant-like state of transmissivity oscillations, resulting from many-body interactions among the metamolecules, characterized by long-range order in space and time. The phenomenon is of interest to the study of dynamic classical many-body states in the strongly correlated regime and applications in all-optical modulation, frequency conversion and timing.So far, a continuous time crystal has only been implemented on a quantum system. Optically driven many-body interactions in a nanomechanical photonic metamaterial now allow the realization of a classical continuous time crystal.

This essay explores the complexity of faith in our time. The continued belief in religion indicates, at least to some extent, the failure of science to fully demonstrate its absoluteness to a convincing degree for many believers. And, in Kantian terms, the reason for that is because it cannot. This essay will focus on the point at which faith and reason intersect and become neither each other nor themselves but share in an unspoken and unintended complicity of belief in order to negotiate the impossible truth of the matter, which is just that—the true is the impossible.

Despite recent tremendous progress in optical imaging and metrology1–6, there remains a substantial resolution gap between atomic-scale transmission electron microscopy and optical techniques. Is optical imaging and metrology of nanostructures exhibiting Brownian motion possible with such resolution, beyond thermal fluctuations? Here we report on an experiment in which the average position of a nanowire with a thermal oscillation amplitude of ∼150 pm is resolved in single-shot measurements with subatomic precision of 92 pm, using light at a wavelength of λ = 488 nm, providing an example of such sub-Brownian metrology with ∼λ/5,300 precision. To localize the nanowire, we employ a deep-learning analysis of the scattering of topologically structured light, which is highly sensitive to the nanowire’s position. This non-invasive metrology with absolute errors down to a fraction of the typical size of an atom, opens a range of opportunities to study picometre-scale phenomena with light.The authors report subatomic precision in measuring the displacement of a nanowire. Such precision is achieved by employing deep-learning enabled analysis of single-shot scattering of topologically structured superoscillatory illumination.

Although vast amounts of information are conveyed by photons in optical fibers, the majority of data processing is performed electronically, creating the infamous ‘information bottleneck’ and consuming energy at an increasingly unsustainable rate. The potential for photonic devices to directly manipulate light remains unfulfilled due largely to a lack of materials with strong, fast optical nonlinearities. In this paper, we show that small-signal amplifier, summator and invertor functions for optical signals may be realized using a four-port device that exploits the coherent interaction of beams on a planar plasmonic metamaterial, assuming no intrinsic nonlinearity. The redistribution of energy among ports can provide nonlinear input-output signal dependencies and may be coherently controlled at very low intensity levels, with multi-THz bandwidth and without introducing signal distortion, thereby presenting powerful opportunities for novel optical data processing architectures, complexity oracles and the locally coherent networks that are becoming part of the mainstream telecommunications agenda. Photonic metamaterials: all-optical transistor, summator and inverter An all-optical device based on a planar plasmonic metamaterial is proposed that has summator, inverter and small-signal amplifier functions. Optical processing of optical data signals is strongly needed to overcome the ‘electronic bottleneck’ in current optical communication systems. Now, researchers at the University of Southampton in the UK and Nanyang Technological University in Singapore have theoretically demonstrated the feasibility of exploiting the coherent interaction of light beams in an ultrathin (substantially subwavelength) plasmonic metamaterial to achieve this. As the proposed device does not use nonlinear optical media, it should be possible to operate it at very low power levels. The energy redistribution between the four ports of the device can provide nonlinear input-output signal dependencies and may be controlled at very low intensity levels with multi-terahertz bandwidth and without distorting the signal.

According to the fundamental Huygens superposition principle, light beams traveling in a linear medium will pass though one another without mutual disturbance. Indeed, the field of photonics is based on the premise that controlling light signals with light requires intense laser fields to facilitate beam interactions in nonlinear media, where the superposition principle can be broken. Here we challenge this wisdom and demonstrate that two coherent beams of light of arbitrarily low intensity can interact on a metamaterial layer of nanoscale thickness in such a way that one beam modulates the intensity of the other. We show that the interference of beams can eliminate the plasmonic Joule losses of light energy in the metamaterial or, in contrast, can lead to almost total absorption of light. Applications of this phenomenon may lie in ultrafast all-optical pulse-recovery devices, coherence filters and terahertz-bandwidth light-by-light modulators.

Chalcogenides—alloys based on group-16 ‘chalcogen’ elements (sulfur, selenium, and tellurium) covalently bound to ‘network formers’ such as arsenic, germanium, antimony, and gallium—have a variety of technologically useful properties, including infrared transparency, high optical nonlinearity, photorefractivity and readily induced, reversible, non-volatile structural phase switching. Such phase-change materials are of enormous interest in the fields of plasmonics and nanophotonics. However, in such applications, the fact that some chalcogenides accrue plasmonic properties in the transition from an amorphous to a crystalline state, i.e., the real part of their relative permittivity becomes negative, has gone somewhat unnoticed. Indeed, one of the most commercially important chalcogenide compounds, germanium antimony telluride (Ge2:Sb2:Te5 or GST), which is widely used in rewritable optical and electronic data storage technologies, presents this behavior at wavelengths in the near-ultraviolet to visible spectral range. In this work, we show that the phase transition-induced emergence of plasmonic properties in the crystalline state can markedly change the optical properties of sub-wavelength-thickness, nanostructured GST films, allowing for the realization of non-volatile, reconfigurable (e.g., color-tunable) chalcogenide metasurfaces operating at visible frequencies and creating opportunities for developments in non-volatile optical memory, solid state displays and all-optical switching devices.

Recently, coherent control of the optical response of thin films in standing waves has attracted considerable attention, ranging from applications in excitation-selective spectroscopy and nonlinear optics to all-optical image processing. Here, we show that integration of metamaterial and optical fibre technologies allows the use of coherently controlled absorption in a fully fiberized and packaged switching metadevice. With this metadevice, which controls light with light in a nanoscale plasmonic metamaterial film on an optical fibre tip, we provide proof-of-principle demonstrations of logical functions XOR, NOT and AND that are performed within a coherent fibre network at wavelengths between 1530 and 1565 nm. The metadevice has been tested at up to 40 gigabits per second and sub-milliwatt power levels. Since coherent absorption can operate at the single-photon level and with 100 THz bandwidth, we argue that the demonstrated all-optical switch concept has potential applications in coherent and quantum information networks. Here, the authors show that integration of metamaterial and optical fibre technologies enables all-optical XOR, NOT and AND logical functions that are performed at up to 40 gigabits per second with few femtojoules per bit energy consumption within a coherent fully fiberized network.

Recent advances in the physics and technology of light generation via free-electron proximity and impact interactions with nanostructures (gratings, photonic crystals, nano-undulators, metamaterials and antenna arrays) have enabled the development of nanoscale-resolution techniques for such applications as mapping plasmons, studying nanoparticle structural transformations and characterizing luminescent materials (including time-resolved measurements). Here, we introduce a universal approach allowing generation of light with prescribed wavelength, direction, divergence and topological charge via point-excitation of holographic plasmonic metasurfaces. It is illustrated using medium-energy free-electron injection to generate highly-directional visible to near-infrared light beams, at selected wavelengths in prescribed azimuthal and polar directions, with brightness two orders of magnitude higher than that from an unstructured surface, and vortex beams with topological charge up to ten. Such emitters, with micron-scale dimensions and the freedom to fully control radiation parameters, offer novel applications in nano-spectroscopy, nano-chemistry and sensing. Controlling the generation of light in nano-scale systems is a challenging task and is of growing importance. Here, Li et al . propose a means of controlling the wavefront of light emanating from a single nano scale emitter by holographic principles using a plasmonic metasurface.

We experimentally demonstrate that standing waves formed by two coherent counter-propagating light waves can take a variety of forms, offering new approaches to the interrogation and control of polarization-sensitive light-matter interactions in ultrathin (subwavelength thickness) media. In contrast to familiar energy standing waves, polarization standing waves have constant electric and magnetic energy densities and a periodically varying polarization state along the wave axis. counterintuitively, anisotropic ultrathin (meta)materials can be made sensitive or insensitive to such polarization variations by adjusting their azimuthal angle.

Surface plasmon polaritons, propagating bound oscillations of electrons and light at a metal surface, have great potential as information carriers for next-generation, highly integrated nanophotonic devices 1 , 2 . Since the term ‘active plasmonics’ was coined in 2004 3 , a number of techniques for controlling the propagation of guided surface plasmon polariton signals have been demonstrated 4 , 5 , 6 , 7 . However, with sub-microsecond or nanosecond response times at best, these techniques are likely to be too slow for future applications in such fields as data transport and processing. Here we report that femtosecond optical frequency plasmon pulses can propagate along a metal–dielectric waveguide and that they can be modulated on the femtosecond timescale by direct ultrafast optical excitation of the metal, thereby offering unprecedented terahertz modulation bandwidth—a speed at least five orders of magnitude faster than existing technologies. The ability to modulate optical plasmons, propagating along a metal–dielectric waveguide, on the femtosecond time scale suggests that plasmons may be a suitable data carrier for future ultrasfast communication applications.