Volume 3 Issue 12, December 2009

Quantum information protocols based on continuous-variable entangled states are attractive because they exploit standard optical modulation and measurement equipment, and do not require single photons. Recent progress in the field is reversing initial concerns about the practicality of the approach.

Recent progress in manipulating quantum states of light and matter brings quantum-enhanced measurements closer to prospective applications. The current challenge is to make quantum metrologic strategies robust against imperfections.

Quantum optics has come a long way since its birth at the beginning of the 1900s. Nature Photonics spoke to Anton Zeilinger to gain some perspective on its progress.

Laser-based Doppler cooling is a popular method for reducing the temperature of atoms, but it is limited to dilute gases. Now, researchers in Germany have demonstrated a laser scheme for cooling a highly dense gas mixture.

The integration of an optically pumped switch in a quantum cascade laser device yields a semiconductor terahertz amplifier that promises to extend the capabilities of time-domain spectroscopy.

Mechanically manipulating the lateral size of the lasing mode of a single-mode terahertz quantum cascade laser provides a new and robust method for widely and continuously tuning its emission wavelength.

The demonstration that polarized laser pulses can control molecular velocities through the dipole force suggests that the cooling of molecules using light may soon be within reach.

We have just witnessed the birth of the first quantum technology based on encoding information in light for quantum key distribution. The quantum nature of light seems destined to continue to have a central role in future technologies. Here we provide a broad review of photonics for quantum technologies touching on topics including secure communication with photons, quantum information processing, quantum lithography and integrated quantum photonics.

This review highlights the recent progress which has been made towards improved single-photon detector technologies and the impact these developments will have on quantum optics and quantum information science.

Quantum memory is important for a range of application including quantum information processing, matching various processes within a quantum devices, as a tool to convert photons to photons-on-demand and for implementation of long-distance quantum communication using quantum repeaters. Here, state-of-the-art optical quantum memory is reviewed.

An amplifier for terahertz pulses is demonstrated using an Auston switch to perform ultrafast gain switching in a quantum cascade laser. The approach may benefit terahertz imaging and sensing schemes as it overcomes the phenomenon of gain clamping, which usually limits the amplification available in a laser.

The first observation of the Hong–Ou–Mandel coalescence of photons with orbital angular momentum (OAM) is demonstrated, and this is exploited for optimal quantum cloning of OAM-encoded qubits. OAM states may function as units of quantum information in higher-dimensional space and allow increased information content per photon.

Mechanisms of distinct resonance in microcavities driven by strongly detuned single quantum dots are not well understood. Investigation of non-resonant dot–cavity coupling of individual quantum dots in micropillars now suggests a dominant role of phonon-mediated dephasing. This new perspective may have implications for single-photon sources, quantum information applications and spectroscopy.

A compact source of 60-fs pulses is demonstrated, based on a semiconductor laser that is mode-locked using a saturable absorber mirror in an external cavity.

A terahertz wire laser with an unprecedented tuning range of ∼137 GHz has been demonstrated. This scheme relies on bringing dielectric or metallic structures into close proximity with the wire, thus modifying the properties of its guided mode.

The detection of light at the single-photon level is important for tasks ranging from fluorescence imaging to quantum information processing, reports Neil Savage.

Photonics currently lacks a way of amplifying terahertz pulses in time-domain spectroscopy. Nathan Jukam from the École Nomale Supérieure in France spoke to Nature Photonics about how his group has achieved a semiconductor-based terahertz amplifier that gives a greatly improved amplification factor.

The optical world has long been the perfect playground for exploring quantum mechanics. Quantum dreams, from communications and teleportation through to computing and metrology, are shaping into reality. This special Focus Issue provides a glimpse into the tremendous progress that has been made and the challenges that remain for the bright future of quantum optics.