Detecting light, photon by photon: Recent progress and what future may hold

Gregor G. Taylor, Robert H. Hadfield

The ability to detect single photons in the mid-infrared spectral range (beyond 2 μm wavelength, photon energy below 0.62 eV) is the key to unlocking a range of emerging scientific applications, from remote sensing LIDAR, molecular spectroscopy, and powerful new approaches to dark matter detection. Conventional detector types, such as semiconductor single-photon avalanche diodes, lose sensitivity at such low photon energy. Superconducting materials, with a much lower characteristic energy gap, hold particular promise. In this Perspective, we focus on recent advances in superconducting nanowire single-photon detectors, which have recently extended single-photon sensitivity up to 29 μm (0.043 eV). We discuss the potential for future advances and strategies to overcome challenges to technological development.

Geoffrey Hunter, Robert L. P. Wadlinger

Yan Liang, Heping Zeng

Andrew Forbes, Isaac M. Nape

Quantum mechanics is now a mature topic dating back more than a century. During its scientific development, it fostered many technological advances that now are integrated into our everyday lives. More recently, over the past few decades, the authors have seen the emergence of a second quantum revolution, ushering in control of quantum states. Here, the spatial modes of light, “patterns of light,” hold tremendous potential: light is weakly interacting and so an attractive avenue for exploring entanglement preservation in open systems, while spatial modes of light offer a route to high dimensional Hilbert spaces for larger encoding alphabets, promising higher information capacity per photon, better security, and enhanced robustness to noise. Yet, progress in harnessing high dimensional spatial mode entanglement remains in its infancy. Here, the authors review the recent progress in this regard, outlining the core concepts in a tutorial manner before delving into the advances made in creation, manipulation, and detection of such quantum states. The authors cover advances in using orbital angular momentum as well as vectorial states that are hybrid entangled, combining spatial modes with polarization to form an infinite set of two-dimensional spaces: multidimensional entanglement. The authors highlight the exciting work in pushing the boundaries in both the dimension and the photon number, before finally summarizing the open challenges, and the questions that remain unanswered.

I. K. Karpenko

N. Imoto, Y. Yamamoto, Susumu Machida +2 more

The authors discuss features of nonclassical photonic communication with overcome shot-noise-limited performance by means of quantum-optic technologies such as squeezing of light and quantum nondemolition (QND) detection of light. Recent research activities on squeezed states and QND detection are also reviewed. >