Volume 7 Issue 7, July 2013

Co-propagating a signal with its phase conjugate along an optical fibre link makes it possible to mitigate unwanted nonlinear distortions and improve the signal-to-noise ratio in long-haul optical communication systems.

Surface-enhanced Raman spectroscopy is normally associated with the enhanced electric fields that arise near metal nanoparticle surfaces. The contribution of field gradients has been unclear, but new research provides insights into their effect.

The spin of the nitrogen–vacancy centre in diamond is a powerful resource for quantum control. However, control over its charge state lags far behind. Appropriating electrical gating techniques used in quantum-dot devices could bridge this gap.

Scientists experimentally demonstrate a scheme that allows the number of qubits encoded per photon to be varied while keeping the overall quantum information constant. They also propose the inverse 'splitting' process.

Small-scale quantum computers made from an array of interconnected waveguides on a glass chip can now perform a task that is considered hard to undertake on a large scale by classical means.

The web of optical fibre networks deployed across Europe is proving useful for experiments in optical metrology and sensing in addition to their primary use of carrying Internet data and telephone calls.

The first true quantum non-demolition measurement of atomic spins by paramagnetic Faraday rotation in a quantum atom–light interface is described. By using an ensemble of ⁸⁷Rb atoms, quantum state preparation and information–damage trade-off are observed beyond their classical limits by 7 and 12 standard deviations, respectively.

Quantum information circuits for ‘quantum joining’ are proposed, in which two qubits of information encoded in the polarization of two photons are re-encoded into the polarization and path degrees of freedom of a single photon, while keeping the overall quantum information constant. The inverse ‘splitting’ process is also proposed.

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.

Frequency-agile, rapid scanning spectroscopy requires no mechanical motion and provides a scanning rate of 8 kHz per cavity mode at a sensitivity of ∼2 × 10^-12 cm^-1 Hz^-1/2, with a scanning range that exceeds 70 GHz. This technique is promising for fast and sensitive trace gas measurements and chemical kinetic studies.

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.

The boson-sampling problem is experimentally solved by implementing Aaronson and Arkhipov's model of computation with photons in integrated optical circuits. These results set a benchmark for a type of quantum computer that can potentially outperform a conventional computer by using only a few photons and linear optical elements.

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.

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.

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 transmission of a pair of phase-conjugated beams is shown to mitigate nonlinear distortion during optical fibre communication, allowing a 400 Gbit s⁻¹ superchannel to be sent over 12,800 km of optical fibre.

High-speed modulation and 4.4 fJ bit⁻¹ data transmission is demonstrated using a photonic-crystal nanocavity laser. Its current threshold of 4.8 µA, modulation current efficiency of 2.0 GHz µA^−0.5 and output power of 2.17 µW may enable on-chip photonic networks in combination with recently developed high-sensitivity receivers.

A laser with a record low energy cost has now been demonstrated by using a laser cavity based on photonic crystals. Shinji Matsuo of NTT Photonics Laboratories in Japan talked to Nature Photonics about its significance.