Photon counting is the key enabler in quantum optics for variety of quantum information applications. It also plays an important role in classical applications involving extremely low light intensities in a wide range of fields including biological imaging and optical communication. Single-photon states are widely employed in quantum information technologies such as quantum key distribution over optical fibers, where the ability to detect single photons is crucial, and many applications require photon number resolving (PNR) detectors.
There are several approaches in order to develop photon counters able to detect high photon number states – Geiger-mode avalanche photodiodes (APDs), by an APD array or by a streak camera. Other approaches employ monitoring the strength of the electrical response to different photon numbers in superconductor detectors, APDs or visual light photon counters.
All the existing detectors time resolution is limited by the electronic response to be longer than several 10ps, so that two single-photon pulses separated less than 10ps will be detected as a two-photon state by a PNR detector. Although the detectors have good performance in short wavelength of visible light, infrared photon counting remains extremely difficult requiring sophisticated approaches such as upconversion which is inefficient.
Three photon absorption (3PA), transforming the optical signal directly into an electrical signal through a third order resonant transition, results in higher sensitivity as well as polarization insensitivity, wide bandwidth and simplicity.
- Polarization insensitivity
- Wide bandwidth
Applications and Opportunities
- Quantum optics and computation
- Biological imaging