The sensitivity of a quantum detector is characterized by its quantum efficiency, which is the probability that an incident photon will be detected. Quantum detectors can achieve very high quantum efficiencies, with some detectors approaching 100%. This means that almost every photon that strikes the detector is detected, making them extremely sensitive.

In comparison, classical detectors, such as photodiodes, have quantum efficiencies that are typically much lower, often below 10%. This means that they only detect a small fraction of the incident photons, making them less sensitive than quantum detectors.

The high sensitivity of quantum detectors makes them essential for a wide range of applications, including:

* Quantum communication, where they are used to detect the faint signals of photons that have been transmitted through optical fibers or free space.

* Quantum imaging, where they are used to create images of objects by detecting the photons that are emitted or reflected by the objects.

* Quantum metrology, where they are used to measure the properties of atoms, molecules, and materials with extremely high precision.

The continued development of quantum detectors is pushing the boundaries of what is possible in the field of quantum technology, enabling new and exciting applications.