Letters in 2013

Highly efficient perovskite solar cells have been fabricated by using room-temperature deposition processes. The cells are based on a layer of methylammonium lead iodide perovskite that is prepared by sublimation in a high-vacuum chamber and sandwiched between two thin organic charge-transport layers.

Single-step fabrication of a multimode quantum resource from the parametric downconversion of femtosecond frequency combs is demonstrated. Each of the 511 possible bipartitions among ten spectral regions is shown to be entangled. Furthermore, an eigenmode decomposition reveals that eight independent quantum channels (qumodes) are subsumed within the comb.

Simultaneous detection of electric and magnetic fields with a subwavelength resolution is achieved by a near-field scanning approach. Additionally, theoretical considerations provide guidelines for designing probes sensitive to specific desired combinations of electric- and magnetic-field components.

A silicon-on-insulator device combining two four-wave-mixing photon-pair sources in an interferometer with a reconfigurable phase shifter is used to create and manipulate non-degenerate or degenerate, path-entangled or path-unentangled photon pairs. A quantum interference visibility of nearly 100% is observed on-chip. This device is a first step towards fully integrated quantum technologies.

Control over the luminescence lifetimes of upconversion nanocrystals allows a new form of temporal multiplexing for imaging and data-storage applications.

Clear evidence is presented for the origins of photocurrent generation in metallic and semiconducting carbon nanotubes — photocurrent is found to be mainly generated by photothermal and photovoltaic effects in metallic and semiconducting carbon nanotubes, respectively. This finding will enable the engineering of highly efficient carbon-based photodetectors and energy-harvesting devices.

Quasi-monoenergetic Compton X-rays tunable in the range ∼70 keV to >1 MeV are generated in a laser-driven scheme.

Room-temperature lasing in core–shell–cap GaAs/AlGaAs/GaAs nanowires is demonstrated using optical pumping. It is realized by employing a Fabry–Pérot cavity along with material optimization and surface recombination minimization. This demonstration should prove useful for designing nanoscale optoelectronic devices operating at near-infrared wavelengths.

A continuous-variable cluster state containing more than 10,000 entangled modes is deterministically generated and fully characterized. The developed time-domain multiplexing method allows each quantum mode to be manipulated by the same optical components at different times. An efficient scheme for measurement-based quantum computation on this cluster state is presented.

The carrier-envelope phase of laser fields at metal tips can affect the generation and motion of strong-field emitted electrons. Observed variations in the width of plateau-like photoelectron spectra characteristic of the sub-cycle regime may lead to the control of coherent electron motion at metallic nanostructures on ultrashort lengths and timescales.

An easily implementable reconstruction scheme is demonstrated for determining the full vectorial amplitude and relative phase distributions of highly confined electromagnetic fields with subwavelength resolution from a single-scan measurement. This scheme will help improve microscopy and nanoscopy techniques.

A new laser-field measurement technique is demonstrated that exploits nonlinear optical mixing in a gas in which attosecond pulses are being generated. The instantaneous field of an unknown pulse is imprinted onto the deflection of an attosecond pulse using an all-optical set-up with a bandwidth of up to 1 PHz.

Two-, three- and higher multiphoton absorption processes are shown to occur in amyloid protein fibres, which are thought to play a role in various diseases, including Alzheimer's and Parkinson's diseases. The nonlinear optical behaviour of such proteins may also be useful for fabricating photonics devices.

A simple, rapid and inexpensive nanolithography technique is demonstrated that exploits nonlinear feedback mechanisms to tightly regulate the formation of nanostructures induced by femtosecond laser pulses. The nonlocal nature of the feedback allows the nanostructures to be seamlessly stitched, resulting in large-area nanostructuring whose periodicity is uniform on a subnanometre scale.

A wireless communication system with a maximum data rate of 100 Gbit s⁻¹ over 20 m is demonstrated using a carrier frequency of 237.5 GHz. The photonic schemes used to generate the signal carrier and local oscillator are described, as is the fast photodetector used as a mixer for data extraction.

Excitation with thermal light from a superluminescent diode is shown to yield enhanced fluorescence from both quantum dots and dyes, potentially enabling higher-sensitivity biological imaging.

The transition between operation in a stable coherent state and that in a disordered turbulent state is studied in a fibre laser. The loss of coherence following the transition is associated with the appearance of solitons, which proliferate and cluster.

A confocal fluorescence microscopy scheme that maps the image to the radiofrequency spectrum by beating together two optical fields offers enhanced read-out speeds at kilohertz frame rates. It provides a new way for observing dynamic phenomena in cells.

A chip-integrated graphene photodetector with a high responsivity of over 0.1 A W⁻¹, high speed and broad spectral bandwidth is realized through enhanced absorption due to near-field coupling. Under zero-bias operation, response rates above 20 GHz and an instrumentation-limited 12 Gbit s⁻¹ optical data link are demonstrated.

A CMOS-compatible photodetector based on graphene with multi-gigahertz operation ranging from the O- to U-band of telecommunication bands is demonstrated, highlighting the promise of graphene as a new material for integrated photonics.