Coherence of Single Photons

  • Thread starter Joseph14
  • Start date
  • #1
51
0
For any light beam it is normal to characterize the coherence length and time. This is done by measuring the ability light to interfere with itself.

Does it make sense to talk about the coherence of a single photon beam, such as the one used in the double slit experiment? Can a single photon beam be incoherent? I imagine this could be tested using a mach-zehnder interferometer.
 

Answers and Replies

  • #2
642
15
A single photon could have a coherence relationship to a varying background field. As an analogy you might look at G. P. Thomson's electron beam experiments where single electrons were fired into a very thin gold foil. The arrangement of the atoms in the foil lattice produced a varying field that interfered with the electron. The result was the creation of visible rings (EM fluctuations) spreading out from the impact point.
 
  • #3
Cthugha
Science Advisor
1,956
319
A single photon state will show ideal first-order coherence in both temporal and spatial domains. In fact, this holds true for any arbitrary pure-state excitation of a single mode and any statistical-mixture state, in which a single mode of the radiation field is excited.

This is discussed for example in chapter 9 of Loudon's "The quantum theory of light" and to some lesser degree in the book about "Mesoscopic quantum optics" by Yoshi Yamamoto and Atac Imamoglu.

It is also discussed in depth in "U. Titulaer and R. Glauber, Density operators for Coherent Fields", Phys Rev, Vol 145, (1966), pp. 1041, but that paper is not an easy read.

However, all single photon states will of course only show first-order, but no second or higher-order coherence. In addition one should also add that real single photon sources are not necessarily creating real Fock states in the sense theory proclaims. Most will produce single photons over a narrow range of energies varying from one photon to the next.
 

Related Threads on Coherence of Single Photons

  • Last Post
Replies
11
Views
2K
  • Last Post
Replies
5
Views
2K
Replies
13
Views
965
Replies
4
Views
2K
  • Last Post
Replies
4
Views
977
Replies
1
Views
683
  • Last Post
Replies
6
Views
3K
  • Last Post
Replies
2
Views
2K
  • Last Post
Replies
15
Views
4K
Replies
4
Views
2K
Top