Atomic-Vapor-Based High Efficiency Optical Detectors with Photon Number Resolution

The ability to detect very weak optical fields with high efficiency ($>99\%$) and to distinguish the number of photons in a given time interval is a very challenging technical problem with enormous potential payoffs in quantum communications and information processing. We propose to employ an atomic vapor as the active medium, prepared in a specific quantum state using laser radiation. The absorption of a photon will be aided by a dressing laser, and the presence or absence of an excited atom will be detected using the “cycling transition” approach perfected for ion traps. By incorporating an appropriate up-conversion scheme, our method can be applied to a wide variety of optical wavelengths.

Figure 1

Diagram illustrating schematically the proposed photodetection technique. The polarizing beam splitter (PBS) dictates the polarizations of the applied optical fields, as assumed in deriving the Hamiltonian Eq. (1).

Figure 2

Diagram illustrating the atomic transitions envisioned for the three-stage photodetection procedure. Stage (a) is optical pumping to level $|1⟩$; stage (b) is the absorption of the photon with the assistance of a classical escort pulse; stage (c) is the detection of any atom in state $|2⟩$.