In classical electromagnetism, the amplitude of an electromagnetic wave represents the maximum value of its electric or magnetic field strength. However, when we discuss photons, which are the fundamental particles of light, their amplitudes are not defined in the same way as for classical waves.
Photons are described by quantum mechanics, which treats them as particles that exhibit wave-particle duality. In this framework, the amplitude of a photon is related to its wave function, which describes the probability distribution of finding the photon at a particular location.
The square of the amplitude of a photon's wave function gives the probability density of detecting the photon at a specific point. However, the actual amplitude of a single photon cannot be measured or directly observed. The intensity or brightness of light, which is related to the number of photons present, can be measured, but the individual amplitudes of photons are not directly accessible.
It's important to note that the amplitude of a classical electromagnetic wave is related to the intensity or energy of the corresponding light. In the quantum realm, the energy of a photon is related to its frequency. The higher the frequency, the higher the energy carried by each individual photon.
So, while we cannot assign a specific amplitude to an individual photon, we can still discuss the intensity or energy of a collection of photons, which relates to the overall brightness or power of the light.