Timeline for Is single photon perfectly monochromatic?
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| Apr 13, 2017 at 12:39 | history | edited | CommunityBot |
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| Jul 3, 2014 at 0:32 | comment | added | garyp | @harshfi6 A mode has a single well-defined frequency. A mixed state describes an ensemble. A pure state can be a superposition of multiple modes. If the superposition is over wavevectors of the same frequency, then it is an energy eigenstate, and can have a well-defined occupation number. I would call the excitations of this state photons. If the superposition is over modes of different frequency, then we don't have energy eigenstates, and well-defined occupation numbers. I wouldn't call excitations of this state photons. | |
| Jul 3, 2014 at 0:25 | comment | added | garyp | @harshfi6 We may be arguing about language. My point of view comes from what I glean from books (Loudon, and Mandel and Wolf). (I may misrepresent them.) My photon: a single excitation of an energy eigenstate / number eigenstate. It has a single frequency, well-defined occupation number, and completely indeterminate phase. Anything else is a state of the field, but not a photon. Note that the states are degenerate. In free space, $\vec{k}$ can point in any direction, or be a superposition thereof, so with boundaries the field can take on non-space-filling shapes (e.g. cavities). | |
| Jul 2, 2014 at 17:04 | comment | added | Harshfi6 | Even if a photon at an instant lies in a single mode, the frequency must have a spread independent of our knowledge, coz otherwise we could say it has a frequency value with infinite accuracy(independent of we can measure it or not) which is not possible. So single wavelength in a single more shouldn't be the case. | |
| Jul 2, 2014 at 15:35 | comment | added | Ruslan | @garyp if the photon lives in one of those modes, but we don't know which one, isn't it a mixed state then? A photon in a pure state may be in superposition of multiple modes, but in this case it doesn't live in one of them. | |
| Jul 2, 2014 at 15:28 | history | edited | Volker Siegel | CC BY-SA 3.0 |
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| Jul 2, 2014 at 15:14 | comment | added | Volker Siegel | @garyp More innocuous, and correct now I guess? :) | |
| Jul 2, 2014 at 15:12 | history | edited | Volker Siegel | CC BY-SA 3.0 |
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| Jul 2, 2014 at 15:06 | history | edited | Volker Siegel | CC BY-SA 3.0 |
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| Jul 2, 2014 at 14:54 | comment | added | garyp | Your penultimate sentence needs some sharpening, I think. As you say, a single photon has a single frequency and wavelength. What you might have physically is a bunch of very closely spaced modes. The photon will live in one of those modes, but we might not know which one. Still, whatever mode is excited it will have a single frequency and wavelength. Photons themselves do not have a spread of frequencies. | |
| Jul 2, 2014 at 14:23 | history | edited | Volker Siegel | CC BY-SA 3.0 |
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| Jul 2, 2014 at 14:13 | history | edited | Volker Siegel | CC BY-SA 3.0 |
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| Jul 2, 2014 at 14:06 | history | answered | Volker Siegel | CC BY-SA 3.0 |