A quantum light source could pave the way for a quantum internet

The ability to integrate fiber-based quantum information technology into existing optical networks would be an important step towards applications in quantum communication. To achieve this, quantum light sources must be able to emit single photons with controllable positioning and polarization and in ranges of 1.35 and 1.55 micrometers where light travels with minimal loss in the arrays of existing optical fibers, such as telecommunications networks. This combination of characteristics has been elusive until now, despite two decades of research efforts.

Recently, two-dimensional (2D) semiconductors have emerged as a new platform for next-generation photonics and electronics applications. Although scientists have demonstrated that 2D quantum emitters operate in the visible regime, single-photon emission in the most desirable telecommunications bands has never been achieved in 2D systems.

To solve this problem, researchers at Los Alamos National Laboratory have developed a constraint engineering protocol to deterministically create two-dimensional quantum light emitters with tunable operating wavelength on the O and C telecommunications bands. The polarization of emissions can be tuned with a magnetic field by exploiting the degree of freedom of the valley.

The researchers achieved a single photon purity of 90% and an operating temperature of 77 Kelvin. These groundbreaking results open the door to exciting developments in quantum technologies.

The research is published in the journal Nature Communication.

Conventional light sources for fiber optic telecommunications emit many photons at the same time. Photons are particles of light that travel in the form of waves. In today’s telecommunications networks, information is transmitted by modulating the properties of light waves traveling in optical fibers, in the same way that radio waves are modulated in AM and FM channels.

In quantum communication, however, information is encoded in the phase of a single photon – the position of the photon in the wave in which it is traveling. This makes it possible to connect quantum sensors in a network covering large distances and to connect quantum computers to each other.

Researchers have recently produced single-photon sources with operating wavelengths compatible with existing fiber communication networks. They did this by placing atom-thick molybdenum ditelluride semiconductor layers just above an array of nanometer-sized pillars. This is the first time that researchers have demonstrated this type of tunable light sources suitable for use in telecommunications systems.

The results of this study make it possible for the first time to integrate quantum light sources made of two-dimensional materials into existing communication networks. In addition, the two-dimensional nature of the material facilitates the construction of devices layer by layer. This could help integrate these light sources into emerging quantum computers to build larger modular computing systems and gain quantum advantage for practical applications.