Scientists at the Hebrew University of Jerusalem have demonstrated a compact, efficient single photon source that is able to operate on a chip at ambient temperatures.

New nano-antenna directs photons in a specific direction in space. Image Credit Hebrew University of Jerusalem.New nano-antenna directs photons in a specific direction in space. Image Credit Hebrew University of Jerusalem.The single photon-source concept is highly directional and the researchers say they believe it will lead to advances in the production of compact, inexpensive, efficient sources of quantum information bits for future applications.

Many artificial sources that create photons used for various quantum information tasks in today’s labs must be maintained at temperatures of about -270 C, requiring large and expensive refrigeration systems. The team’s compact single photon source operates efficiently at room temperature.

The researchers used nanocrystals of semiconducting materials and developed a method to position a single nanocrystal on top of a specially designed and fabricated nanoantenna. The nanoantenna is able to direct single photons from the nanocrystals into a well-defined direction in space. When combined, the nanocrystals-nanoantenna device can produce a highly directional stream of single photons. The photons all fly in the same direction with a low divergence angle. The photons are collected with an optical setup, and sent for detection and analysis using single photon detectors.

The hybrid antenna enhances collection efficiency of single photons by more than a factor of 10 when compared to a single nanocrystal without the antenna. Additionally, the process eliminates the need for complex and bulky optical collection systems. Experimental results show nearly 40% of the photons are collected with a simple optical apparatus, while more than 20% of the photons are emitted into a low numerical aperture: this represents a 20-fold improvement over a freestanding quantum dot, with a probability of more than 70% for a single photon emission, researchers say. They found single photon purity is only limited by emission from the metal, which is an obstacle that can be bypassed with careful design and fabrication.