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High-quality narrow bandwidth single-photon states with tunable frequency are essential for quantum and atomic technologies. Using a whispering gallery mode resonator, Förtsch et al. build such a source with wavelength tuning across 100 nm and controllable narrow bandwidth.

Looped trajectories of photons in a three-slit interference experiment could modify the resulting intensity pattern, but they are experimentally hard to observe. Here the authors exploit surface plasmon excitations to increase their probability, measuring their contribution and confirming Born’s rule.

Nonlinear interactions such as parametric down-conversion and four-wave mixing are limited by transverse and longitudinal walk-off effects. Here, Pérez et al. demonstrate bright, tunable, diffraction-limited twin-beam radiation by ensuring that signal or idler pulse propagates in the direction or velocity of the pump.

High-refractive-index nanoantennas support magnetic and electric resonances that can be excited with structured light. Here, the authors exploit the interference of such resonances to achieve strong lateral directionality of the emission and utilize this effect for nanoscopic position sensing.

The effect of loss on quantum states is one of the major hurdles in quantum communications. A quantum error-correcting code that overcomes erasure due to photon loss is experimentally demonstrated. The scheme uses linear optics and protects a four-mode entangled mesoscopic state of light.

Two independent experiments demonstrate that quantum entanglement that has been lost in decoherence processes can be recovered. For the first time such ‘entanglement distillation’ has been achieved for states of light that are entangled in continuous variables, which should help to increase the distance over which quantum information can be distributed.

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.

An ion trap has been built and characterized in which the atom sits on the top of a stylus-like electrode. The design should find application in the construction of efficient light–matter interfaces and field sensors, where good access to the ion is crucial.

Amplifying a signal usually also amplifies the noise. A quantum-state amplifier is now demonstrated that can actually decrease uncertainty about the state’s phase. Counterintuitively, the concept involves the addition of thermal noise.

Researchers demonstrate random-number generation by exploiting the intrinsic randomness of vacuum states. The approach may lead to reliable and high-speed quantum random-number generators for applications ranging from gambling to cryptography.

Resistance to turbulence is an ongoing challenge for point-to-point freespace communications. Here the authors present a protocol for encoding a large amount of information in vector beams that are transmittable through a moderately strong turbulent channel without adaptive beam compensation.

A low-power, fixed microwave signal in combination with an optical-pump signal generates an optical frequency comb that spans the whole wavelength range of the telecommunications C-band, with possible applications ranging from spectroscopy to optical communications.

This Progress Article details the latest achievements and underlying principles of light carrying transverse spin.The capabilities and future applications of this young yet already advanced field are highlighted.