Letters in 2013

A CMOS-compatible graphene/silicon-heterostructure photodetector formed by integrating graphene onto a silicon optical waveguide on silicon-on-insulator and operating in the near- and mid-infrared regions is demonstrated. A responsivity as high as 0.13 A W⁻¹ is obtained at a bias of 1.5 V for 2.75-μm light at room temperature.

Femtosecond laser pulses were used to heat dense matter, converting it into an extremely hot plasma. 52-times ionized gold was achieved as well as gigabar pressures, which can be exceeded only in the central hot spots of thermonuclear fusion plasmas.

A chip-compatible beamsplitter that can separate left- and right-handed circularly polarized light is promising for constructing more sophisticated integrated optical circuits. The prism-shaped device, which operates around the telecommunication wavelength of 1.5 μm, consists of a photonic crystal composed of an array of helical structures.

Previously demonstrated zero- or negative-refractive-index metamaterials at optical frequencies suffer from large ohmic losses because of the need to use metals. Metamaterials formed by stacked silicon rod unit cells allow the realization of all-dielectric impedance-matched zero-index metamaterials operating at optical frequencies, potentially benefiting the development of angular-selective optical devices.

Gradientless light fields are shown to exert pulling forces on arbitrary objects in purely passive dielectric media. These forces arise from amplification of the photon linear momentum when light is scattered from one dielectric to another with a higher refractive index. They can manipulate objects over macroscopic distances along dielectric interfaces.

Off-resonant femtosecond magnetization dynamics are observed after applying an ultra-intense, phase-stable terahertz laser field to ferromagnetic cobalt films. The laser's phase and field-strength characteristics are directly imprinted onto the magnetization response. The off-resonant magnetization removes the speed limitation caused by the cooling process, providing new opportunities for ultrafast data storage.

The rotational Doppler frequency shift is observed for a circularly polarized lightwave propagating through a gas of synchronously spinning molecules by using a linearly polarized pulsed laser beam to align diatomic molecules and a linearly polarized pulse to induce concerted unidirectional rotation.

An organic field effect transistor featuring the chiral molecule helicene acts as a photodetector that is able to distinguish between left- and right-handed circularly polarized light.

Squeezed states of light have been experimentally demonstrated to improve the performance of the Laser Interferometer Gravitational-wave Observatory (LIGO) in astrophysically relevant frequency regions. This enhanced performance may help to reach the sensitivity required for detecting gravitational waves.

Nonlinear optics can overcome the diffraction limit through the presence and interaction of many photons. Abbe's diffraction theory is now generalized to include spatial nonlinearity, and wave mixing is treated as a self-induced structured illumination, thereby allowing a standard imaging system to be nonlinearly enhanced beyond its conventional limits.

An ultrafast terahertz (THz) scanning tunnelling microscope (STM) with subpicosecond time resolution and nanometre spatial resolution has been developed. THz pulses are coupled to the metal tip of a commercial STM and THz-pulse-induced tunnelling is observed in the STM. The THz-STM can directly image ultrafast carrier capture by a single InAs nanodot.

Artificially reducing the effective dimensionality of carbon nanotubes from one to zero dimensions increases the luminescence quantum yield of excitons confined in zero-dimensional-like states to ∼18%, which is over one order of magnitude larger than that of intrinsic one-dimensional excitons (∼1%). This finding will help realize future nanoscale photonic devices.

Spatially coherent 11.45 nm radiation is produced by outcoupling the harmonics of cavity-enhanced nonlinearly compressed pulses from a Yb-based laser through a pierced cavity mirror. This technique may lead to high-photon-flux ultrashort-pulse extreme-ultraviolet sources for use in a wide range of applications.

A highly efficient method is demonstrated for detecting individual photons scattering from short-lived transitions in single trapped ions. An entangled state is used to amplify the tiny momentum kick an ion receives on scattering a photon. Cat-state spectroscopy has an 18-fold higher measurement sensitivity than the direct detection method.

Researchers demonstrate a laser interferometer that achieves simultaneous nonclassical readout of two conjugated observables. Because their system uses steady-state entanglement, it does not require any conditioning or post-selection. By distinguishing between scientific and parasitic signals, its sensitivity exceeds the standard quantum limit by about 6 dB.

Single and tandem dye-sensitized solar cells with high power-conversion efficiencies and large photocurrent densities are fabricated using a photosensitizer whose long wavelength absorption originates from a spin-forbidden single–triplet transition.

A fibre-laser-pumped optical parametric amplifier for high-harmonic generation has been used to realize a megahertz-repetition-rate source of extreme-ultraviolet continua, with evidence of isolated attosecond pulses at 0.6 MHz. This technique could potentially enable a vast array of new applications, such as attosecond-resolution coincidence and photoelectron spectroscopy.

The boson-sampling problem was demonstrated by studying three-photon interference in a five-mode integrated interferometer containing three-dimensional S-bent waveguides. Three single photons were input into the interferometer and the probability ratios of all events were measured. The results agree with quantum mechanical predictions for three-photon interference.

An array of pyramidal site-controlled InGaAs_1−δN_δ quantum dots is grown on a GaAs substrate to reduce the fine-structure splitting of the intermediate single-exciton energy levels to less than 4 μeV. The quantum dots emit polarization-entangled photons at a maximum fidelity of 0.721 ± 0.043 without external manipulation of the electronic states.

Raman spectroscopy reveals selection-rule breakdown in the transitions of an isolated single-walled carbon nanotube. The breakdown may be caused by metal dimers and the high field gradient in the radial direction of the tubes.