Letters in 2010

Scientists report a mode-locking regime of an erbium-doped fibre laser in which the laser pulse evolves as a similariton in the gain segment of the cavity and transforms into a soliton in the rest of the cavity. The findings constitute the first observation of amplifier similaritons in a laser cavity and are likely to be applicable to various other nonlinear systems.

A Yagi–Uda directional antenna — the work horse of radiofrequency communications for more than 60 years — has now been demonstrated at visible wavelengths. An array of appropriately tuned nanoparticles replicate the reflecting and directing elements of the original design. Directional control of radiation from the nano-optical Yagi–Uda antenna was experimentally shown.

Entangled photons are efficiently generated from highly symmetric, site-controlled InGaAs/GaAs quantum dots grown in inverted pyramids. Fine-structure splitting of the intermediate exciton level is suppressed without the application of electric, magnetic or strain fields. Polarization entanglement is demonstrated by measurements of the two-photon density matrix and the confirmation of several entanglement criteria.

Quantum memories for storing and releasing photons are required for quantum computers and quantum communications. So far, their operational bandwidths have limited data-rates to megahertz. Researchers now demonstrate coherent storage and retrieval of subnanosecond low-intensity light pulses with spectral bandwidths exceeding 1 GHz.

Sub-shot-noise imaging using spatial quantum correlations between parametric down-conversion light beams is demonstrated. The scheme exhibits a larger signal-to-noise ratio than is possible through classical imaging methods.

Organic light-emitting diodes featuring layers with a spontaneously formed buckled geometry are demonstrated to offer at least a twofold improvement in light extraction efficiency across the entire visible spectrum.

Light is scattered out of a focusing beam when an inhomogeneous medium is placed between the lens and the focal plane. Now, scientists experimentally demonstrate that scattering can be exploited to improve, rather than deteriorate, the focusing resolution of a lens by using wavefront shaping to compensate for scattering.

Distillation of entangled photons is essential for applications such as long-distance quantum communication and high-fidelity quantum teleportation. Distillation from Gaussian input states is experimentally realized, resulting in a large gain in entanglement.

The lack of effcient solid-state sources of single photons is impeding the further development of many fields including quantum communication, quantum information processing and metrology. Using an InAs quantum dot embedded in a GaAs photonic nanowire with carefully tailored ends, researchers demonstrate a record single-photon source effciency of 0.72 under optical pumping.

The first enhancement cavity for femtosecond ultraviolet pulses is demonstrated. More than 7 W of average ultraviolet power at an 81 MHz repetition rate, available to pump a nonlinear crystal inside the cavity, is exploited in an implementation of a powerful source for high-rate experiments with entangled multiphoton states.

Researchers have constructed a terahertz quantum cascade laser using quasi-periodic distributed feedback gratings based on the Fibonacci sequence. Features that go beyond traditional distributed feedback lasers are demonstrated, such as directional output independent of the emission frequency and multicolour operation.

The generation of spatiotemporal optical wave packets that are resistant to both dispersion and diffraction are attractive for bioimaging applications and plasma physics. By combining Bessel beams in the transverse plane with temporal Airy pulses, scientists now report the first observation of a class of versatile three-dimensional linear light ‘bullets’.

Active switching of plasmons by an external magnetic field is demonstrated in a metal–ferromagnet–metal structure. The strong modulation, combined with possible all-optical magnetization reversal induced by femtosecond light pulses, opens the door to ultrafast magneto-plasmonic switching.

By exploiting the Stark manifold resonance in a crystalline host, scientists report laser cooling of ytterbium-doped LiYF₄ crystals from room temperature to ∼155 K, with a cooling power of 90 mW. This is the lowest temperature achieved without using cryogens or mechanical refrigeration, surpassing the performance of multistage Peltier coolers.

A quantum cascade laser with a wall-plug efficiency of up to 50% is experimentally realized when operated at low temperatures and in pulsed mode. The high-efficiency performance is achieved by implementing an ultrastrong coupling between the injector and active regions.

A matterless double-slit scenario is proposed, in which photons generated from head-on collisions between a probe laser field and two ultraintense laser beams form a double-slit interference pattern. Such electromagnetic fields are predicted to induce material-like behaviour in a vacuum, supporting elastic scattering between photons.

A mid-infrared quantum cascade laser that emits more light than heat and features a high wall-plug efficiency of up to 53% when operated a temperature of 40 K is reported. The device utilizes a single-well injector design.