Could someone please help to clarify the difference between a photon and a quanta? Below is my current understanding – please correct me if I am wrong.
A photon – is a 'wave particle' of 'light'. I can be defined by its waveform frequency, however its waveform can be complex or simple.
Note: the frequency of a wave is proportional to the energy of the wave. The energy of a waveform is related to the momentum of is respective particle form.
Note: A complex waveform can be deconstructed into simple harmonic components (simple sine waves), within the complex waveform
A wave packet – is a collection of photons 'grouped' together. A packet consists of a 'sum' of random simple harmonic components at the same frequency.
Note: Some packets or 'packet components' may occur more frequently due to the nature of quantum particles. I.e. position (and thus harmonic component) is based upon probability – defined by waveform amplitude.
Quanta – is a collection of random wave-packets 'held' together to meet a 'minimum energy' required for interaction.
Does this sounds right?
Thanks in advance.
Best Answer
A "particle" is a concept that only exists in classical mechanics. There it means that we are approximating the motion of an extended piece of matter (what we call "a body") by the trajectory of its center of mass, i.e. we are completely neglecting all internal degrees of freedom, the composition and we don't even care about rotations. Planets in the Kepler problem are "particles", photons are not.
One step up from "particles" reside the "rigid bodies", for which we deal with rotation and then, in continuum mechanics, we introduce deformations of elastic (and inelastic) solid bodies and "fluids", i.e. liquids and gases. Each time we include more degrees of freedom the mathematical description gets significantly more complicated and the phenomenological behavior of the corresponding matter gets richer.
Wave packets or "wavelets" are a somewhat vague concepts in classical field descriptions. They kind of seem to have a "center of mass", that kind of can look like they move like a particle if we squint on both eyes, but we almost never consider their proper behavior in media with dispersion because, at the end of the day, they are not as simple as particles and they don't behave in ways that make them as useful for applications in physics as the particle approximation.
For completeness sake, there is a mathematical procedure called a "wavelet transform" that works similar to a Fourier transform and that has very nice properties, but I am not sure if one can make it physically useful as it neglects the physical dynamics of the wavelets completely. They are merely used as kernels in a linear transformation, just like the periodic functions are used in Fourier transforms.
Finally, photons are not wave packets but quanta. Their main property is that they denote a finite amount of energy and, even more importantly, a certain amount of angular momentum that is being exchanged in the interaction between a quantum field and matter (which, strictly speaking, is also described by quantum fields). In this sense photons are "properties" or local measurements that describe dynamic processes. One should think of them similarly as one thinks about the conversion of kinetic and potential energy in classical mechanics. Instead of allowing arbitrary amounts of work being done by one system on another, quantum field theory limits it to small, but finite amounts... those are the "quanta". Quanta are therefor not "objects", but properties of objects or properties of the dynamics of objects.
From an experimental point of view a photon is the smallest measurement (or preparation) one can make on a quantized electromagnetic field because the measurement device is made of matter. One can therefor also think about photons as part of the state of the quantized electromagnetic field, but that, too, oversimplifies the mathematical framework that describes these field.