Letters in 2012

Recent theory predicts that Einstein–Podolsky–Rosen arguments enable an effect in which one party can steer the other but not the converse. Researchers have now demonstrated this one-way steering effect with two entangled Gaussian modes of light, potentially opening up a new field of applications in quantum information.

The realization of GaAs lasers on a silicon substrate using a print transfer process offers an alternative wafer-bonding technique for the hybrid integration of optoelectronics.

Researchers demonstrate coherent X-ray surface scattering imaging in a grazing-incidence geometry that takes advantage of enhanced X-ray surface scattering and interference near total external reflection. Surface patterns are reconstructed in three dimensions with nanometre resolution. The approach has applications in the analysis of buried nano-electronic and nanophotonic structures.

Researchers report the first demonstration of an ultrafast all-optical switch in the single-photon regime. The device, which consists of an InAs/GaAs quantum dot in a photonic crystal defect cavity, exhibits a coherent coupling constant of 141 meV and a quality factor of 25,000. The overall switching time is around 50 ps.

Researchers realize transmission eigenchannels in a disordered medium and demonstrate that a single eigenchannel can transport 3.99 times more energy than uncontrolled waves. This work opens up new avenues for enhancing light-energy delivery to biological tissues and controlling the lasing threshold in random lasers.

Researchers provide experimental evidence of intrinsic linewidths approaching the quantum limit in a GaAs/AlGaAs quantum cascade laser emitting at 2.5 THz. Despite the expected dominant broadening effect induced by thermal photons, the measured intrinsic linewidth is 90 Hz — even narrower than that of a semiconductor laser working at significantly shorter wavelengths.

Researchers demonstrate all-optical wavelength conversion based on a resonant nonlinear process within a terahertz quantum cascade laser. The wavelength of the pump beam (812 nm) corresponds to the interband transitions of the laser. The researchers measured a power-conversion efficiency of 0.13% in the range of 812–818 nm, which is the highest value obtained for such a device.

Researchers show that wavefront shaping enables not only real-time widefield imaging through turbid layers with both coherent and incoherent llumination, but also the imaging of objects outside the line-of-sight using light scattered from diffuse walls.

By constructing a thermal emission control device based on a multiple-quantum-well layer embedded in a two-dimensional photonic crystal, researchers demonstrate that they can convert a broadband thermal emission spectrum into a narrowband spectrum with minimal loss of energy.

Researchers use energy-dispersive X-ray spectroscopy to detect X-ray emission from a single erbium atom. Although the measured intensities are relatively weak, the work may allow single-atom X-ray spectra to be obtained from other atomic species.

The fabrication of nanoscale p–n junctions from colloidal nanocrystals and quantum dots provides a new architecture for efficient, solution-processed solar cells.

Researchers report sub-ångström fundamental-wavelength lasing at the SPring-8 Angstrom Compact Free-Electron Laser in Japan. The output has a maximum power of more than 10 GW, a pulse duration of 10⁻¹⁴ s and a lasing wavelength of 0.634 Å.

Researchers report a three-dimensional metal–dielectric optical cavity with an ultrahigh optical index of 17.4. The resonant frequency of the cavity is constant and independent of its size. This unique property could be used to provide significant enhancements to a broad range of light–matter interactions.

Researchers report the spontaneous appearance of discrete frequency modes in a real-time experimental investigation of pulsed modulation instability in an optical system. These findings are expected to impact modulation instability-induced characteristics across a broad range of physical situations and technological systems, including free-electron lasers.

Researchers demonstrate an ultrastrong optical trap capable of operating with nanonewton optical forces by employing tailor-made high-refractive-index particles. This work could could lead to the development of highly efficient light-driven machines.

Researchers demonstrate spontaneous emission enhancements approaching 1,000 for emitters coupled to the gap between a metal wire and a metal substrate. The enhanced emission rate of plasmons in the structures is shown to yield a high internal quantum efficiency, despite the close proximity of lossy metal surfaces.

Researchers investigate the internal gain of InAsP quantum dots embedded in an InP nanowire by performing photocurrent measurements down to the single-photon regime. The resulting gain ( > 10⁴) is a significant step towards single-shot electrical read-out of an exciton qubit state for the transfer of quantum information between flying and stationary qubits.

By developing full quantum detector tomography, researchers simultaneously characterize the wave- and photon-number sensitivities of quantum-optical detectors to yield the largest ever parametrization in a quantum tomography experiment. The presented results reveal the role of coherence in quantum measurements and demonstrate the tunability of hybrid quantum-optical detectors.

Using only conventional semiconductor processing on a silicon wafer, researchers successfully fabricate an on-chip resonator with a record Q-factor of 875 million — around 20 times higher than previous results. They also demonstrate stimulated Brillouin lasers as an example application to emphasize the size control feature of the fabrication method and the ultrahigh-Q available from these resonators.

Lasing in X-ray free-electron lasers is typically achieved by self-amplification of spontaneous emission, which is known to have non-ideal temporal coherence and suffer from beam fluctuations. Here researchers report lasing based on echo-enabled harmonic generation at the Shanghai Deep Ultraviolet free-electron laser facility.