Volume 8 Issue 2, February 2014

Michele Svandrlik and Fulvio Parmigiani, respectively Project Director and Head of Science at FERMI, talk to Nature Photonics about building the first fully coherent seeded free-electron laser that outputs soft X-rays.

Reports of perovskite solar cells fabricated at temperatures compatible with polymer substrates indicate that high-performance flexible cells are now an exciting proposition. However, increasing the cell area and stability and addressing environmental concerns are aspects requiring attention.

An engineered defect in silicon carbide that acts as an artificial molecule is found to be the brightest room-temperature source of single photons presently available in a bulk material. This finding suggests that silicon carbide has a promising future for applications in quantum information processing.

Quantum information processing provides novel methods for pumping heat and refrigerating photons. Devices that obtain and manipulate information at the quantum level can function as quantum 'Maxwell's demons' to cool systems in ways that liquid helium cannot.

Researchers have demonstrated high-harmonic generation using strong terahertz pulses in a bulk solid without damaging it. The mechanism underpinning such an extreme nonlinearity also generates coherent electromagnetic radiation covering the terahertz, infrared and optical regions.

Optical generation of hot electrons in metallic structures and its potential as an alternative to conventional electron–hole separation in semiconductor devices are reviewed. The possibilities for realizing high conversion efficiencies with low fabrication costs are discussed along with challenges in terms of the materials, architectures and fabrication methods

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.

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.

A universal pseudo-cooling method based on a Maxwell-demon-like swapping sequence is proposed. A controlled Hamiltonian gate is used to identify lower energy states of the system and to drive the system to those states. An experimental implementation using a quantum optical network exhibits a fidelity higher than 0.978.

Terahertz waveforms with peak fields of 72 MV cm⁻¹ and a central frequency of 30 THz drive interband polarization in bulk GaSe off-resonantly and accelerate excited electron–hole pairs, inducing dynamical Bloch oscillations. This results in the emission of phase-stable, high-harmonic transients over the whole frequency range of 0.1–675 THz.

A means for localizing fluorescent molecules over distances of hundreds of nanometres exploits the energy transfer between a donor molecule and surface plasmons on a metal film. The technique is demonstrated by using it to profile the membranes of living cells.

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.

The use of a thin layer of zinc oxide nanoparticles as an electron-transport layer allows flexible perovskite solar cells to be fabricated with a power conversion efficiency as high as 15.7%.

Little is known about triplet excitons in semiconducting single-walled nanotubes, despite their importance in various applications. The pump–probe and spin-sensitive photoluminescence of such nanotubes is studied, and the quantum yield of triplet formation, triplet lifetime and triplet exciton size are found to be 5 ± 2%, 30 ± 10 µs and 0.65 nm, respectively.

Temporal dissipative solitons are observed in a nonlinear, high-finesse, optical microresonator driven by a continuous-wave laser. This approach enables ultrashort pulses to be generated in spectral regimes lacking broadband laser gain media and saturable absorbers, making it potentially useful for applications in broadband spectroscopy, telecommunications, astronomy and low-phase-noise microwave generation.

A dual-wavelength fibre laser source has been developed for stimulated Raman scattering microscopy. It is precisely tunable over the entire high-wavenumber region of Raman spectra, where most stimulated Raman scattering imaging is performed. Imaging speeds of up to 1 frame s⁻¹ with shot-noise-limited sensitivity were achieved.

On-chip quantum interference between integrated photon sources has now become a reality. Mark Thompson spoke to Nature Photonics about the realization of and future outlook for integrated quantum optics.