Quantum technologies based on photons are anticipated in the areas of information processing, communication, metrology, and lithography. While there have been impressive proof-of-principle demonstrations in all of these areas, future technologies will likely require an integrated optics architecture for improved performance, miniaturization and scalability. We demonstrated highfidelity silica-on-silicon integrated optical realizations of key quantum photonic circuits, including two-photon quantum interference with a visibility of 94.8±0.5%; a controlled-NOT gate with logical basis fidelity of 94.3 ± 0.2%; and a path entangled state of two photons with fidelity > 92%.Quantum information science [1] has shown that harnessing quantum mechanical effects can dramatically improve performance for certain tasks in communication, computation and measurement. However, realizing such quantum technologies is an immense challenge, owing to the difficulty in controlling quantum systems and their inherent fragility. Of the various physical systems being pursued, single particles of light-photons-are often the logical choice, and have been widely used in quantum communication [2], quantum metrology [3,4,5], and quantum lithography [6] settings. Low noise (or decoherence) also makes photons attractive quantum bits (or qubits), and they have emerged as a leading approach to quantum information processing [7].In addition to single photon sources [8] and detectors [9], photonic quantum technologies will rely on sophisticated optical circuits involving high-visibility classical and quantum interference. Already a number of photonic quantum circuits have been realized for quantum metrology [3,4,10,11,12,13], lithography [6], quantum logic gates [14,15,16,17,18,19,20], and other entangling circuits [21,22,23,24]. However, these demonstrations have relied on large-scale (bulk) optical elements bolted to large optical tables, thereby making them inherently unscalable and confining them to the research laboratory. In addition, many have required the design of sophisticated interferometers to achieve the sub-wavelength stability required for reliable operation.We demonstrated the fundamental building blocks of photonic quantum circuits using silica waveguides on a silicon chip: high visibility (98.5±0.4%) classical interference; high visibility (94.8±0.5%) two photon quantum interference; high fidelity controlled-NOT (CNOT) entangling logic gates (logical basis fidelity F = 94.3 ± 0.2%); and on-chip quantum coherence confirmed by high fidelity (> 92%) generation of a two-photon path entangled state. The monolithic nature of these devices means that the correct phase can be stably realized in what would otherwise be an unstable interferometer, greatly simplifying the task of implementing sophisticated photonic quantum circuits. We fabricated 100's of devices on a single wafer and find that performance across the devices is robust, repeatable and well understood.A typical photonic quantum circuit takes several optical paths or "modes" (some...

General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. The development of flat, compact beam-steering devices with no bulky moving parts is opening up a new route to a variety of exciting applications, such as LIDAR scanning systems for autonomous vehicles, robotics and sensing, freespace, and even surface wave optical signal coupling. In this paper, the design, fabrication and characterization of innovative, nonvolatile, and reconfigurable beam-steering metadevices enabled by a combination of optical metasurfaces and chalcogenide phase-change materials is reported. The metadevices reflect an incident optical beam in a mirror-like fashion when the phase-change layer is in the crystalline state, but reflect anomalously at predesigned angles when the phase-change layer is switched into its amorphous state. Experimental angleresolved spectrometry measurements verify that fabricated devices perform as designed, with high efficiencies, up to 40%, when operating at 1550 nm. Laserinduced crystallization and reamorphization experiments confirm reversible switching of the device. It is believed that reconfigurable phase-change-based beam-steering and beam-shaping metadevices, such as those reported here, can offer real applications advantages, such as high efficiency, compactness, fast switching times and, due to the nonvolatile nature of chalcogenide phasechange materials, low power consumption.

We report a broadband polarization-independent perfect absorber with wide-angle near unity absorbance in the visible regime. Our structure is composed of an array of thin Au squares separated from a continuous Au film by a phase change material (Ge2Sb2Te5) layer. It shows that the near perfect absorbance is flat and broad over a wide-angle incidence up to 80° for either transverse electric or magnetic polarization due to a high imaginary part of the dielectric permittivity of Ge2Sb2Te5. The electric field, magnetic field and current distributions in the absorber are investigated to explain the physical origin of the absorbance. Moreover, we carried out numerical simulations to investigate the temporal variation of temperature in the Ge2Sb2Te5 layer and to show that the temperature of amorphous Ge2Sb2Te5 can be raised from room temperature to > 433 K (amorphous-to-crystalline phase transition temperature) in just 0.37 ns with a low light intensity of 95 nW/μm2, owing to the enhanced broadband light absorbance through strong plasmonic resonances in the absorber. The proposed phase-change metamaterial provides a simple way to realize a broadband perfect absorber in the visible and near-infrared (NIR) regions and is important for a number of applications including thermally controlled photonic devices, solar energy conversion and optical data storage.

Micelles formed by the self-assembly of block copolymers in selective solvents have attracted widespread attention and have uses in a wide variety of fields, whereas applications based on their electronic properties are virtually unexplored. Herein we describe studies of solution-processable, low-dispersity, electroactive fibre-like micelles of controlled length from π-conjugated diblock copolymers containing a crystalline regioregular poly(3-hexylthiophene) core and a solubilizing, amorphous regiosymmetric poly(3-hexylthiophene) or polystyrene corona. Tunnelling atomic force microscopy measurements demonstrate that the individual fibres exhibit appreciable conductivity. The fibres were subsequently incorporated as the active layer in field-effect transistors. The resulting charge carrier mobility strongly depends on both the degree of polymerization of the core-forming block and the fibre length, and is independent of corona composition. The use of uniform, colloidally stable electroactive fibre-like micelles based on common π-conjugated block copolymers highlights their significant potential to provide fundamental insight into charge carrier processes in devices, and to enable future electronic applications.

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