Detecting Single Phonons: Is It Possible?

In summary, the conversation discusses the possibility of detecting a single phonon at a well-defined position. Although phonons do not have well-defined positions, it is possible to detect them at a well-defined momentum. Some proposed methods for single phonon detection include Raman scattering, Mössbauer effect, and photon counting systems such as superconducting nanowire detectors.
  • #1
Demystifier
Science Advisor
Insights Author
Gold Member
14,129
6,621
Is it possible to detect a single phonon? If yes, can it be detected at a well-defined position?
 
Physics news on Phys.org
  • #2
I don't know the answer but I'm watching the thread because I think it's an interesting question. I would,however, like to offer some initial thoughts:
1. I think the observation of phonons is known of only indirectly for example by observations of things such as sound propagation and specific heat capacities.
2. Perhaps more observational details can be obtained by observing vibrations of particles that carry the vibrations from place to place. X ray diffraction techniques come to mind.
3. The concept of phonons is probably useful but I'm wondering whether they are actually real things and by that I mean whether it is possible, if only in principle, to actually observe them directly.
 
  • #3
I remember some "listening with a 'quantum ear'": “Local probing of propagating acoustic waves in a gigahertz echo chamber”, Nature Physics 8, 338–343 (2012)
 
  • #4
Dadface said:
3. The concept of phonons is probably useful but I'm wondering whether they are actually real things and by that I mean whether it is possible, if only in principle, to actually observe them directly.
In principle, a phonon should be possible to detect if there is an interaction of the form
$$H_{\rm int}\propto a_{\rm phonon} b^{\dagger}b + h.c.$$
where ##a_{\rm phonon}## is the destruction operator for the phonon, while ##b## and ##b^{\dagger}## are the destruction and creation operators of some quanta which can absorb and emit phonons. Can someone give an actual example of such an interaction?

Such an interaction can detect a phonon at a well-defined position if the above are local operators, i.e.
$${\cal H}_{\rm int}(x)\propto a_{\rm phonon}(x) b^{\dagger}(x)b(x) + h.c.$$
where ##b(x)## etc are Fourier transforms of the usual operators ##b_k## etc in the momentum space. Examples?
 
Last edited:
  • #5
Lord Jestocost said:
I remember some "listening with a 'quantum ear'": “Local probing of propagating acoustic waves in a gigahertz echo chamber”, Nature Physics 8, 338–343 (2012)
As far as I can see, this doesn't have much to do with single phonons.
 
  • #7
Dadface said:
In the abstract they talk about "coherent phonons in SWNT ensembles". I'm not sure what do they mean by that, but it doesn't sound like a single phonon to me.

EDIT: Indeed, by little googling I found
https://arxiv.org/pdf/1205.6023.pdf
where Eq. (2.1) shows that coherent phonons is a state with an uncertain number of phonons. I want exactly one phonon, not an uncertain number of them.
 
Last edited:
  • #9
Demystifier said:
Is it possible to detect a single phonon? If yes, can it be detected at a well-defined position?
Phonons are collective lattice motions with well-defined momenta. Thus individual phonons are localized in reciprocal space, not real space.

As for detecting a phonon, why isn't Raman scattering acceptable? It involves either creation (Stokes) or annihilation (anti-Stokes) of a phonon via inelastic photon scattering. Theoretically, you could do the experiment with a single photon, though the cross section of Raman scattering is several orders of magnitude smaller than Rayleigh scattering.
 
  • Like
Likes vanhees71
  • #10
TeethWhitener said:
Phonons are collective lattice motions with well-defined momenta.
Phonon (just like photon) does not need to have a well-defined momentum. A superposition of one-phonon states with different momenta is still one phonon.
 
  • #12
TeethWhitener said:
As for detecting a phonon, why isn't Raman scattering acceptable? It involves either creation (Stokes) or annihilation (anti-Stokes) of a phonon via inelastic photon scattering. Theoretically, you could do the experiment with a single photon, though the cross section of Raman scattering is several orders of magnitude smaller than Rayleigh scattering.
Theoretically, yes. But I would like to know if something like that has been done in practice.
 
  • #13
How about Mössbauer effect, specifically the phonon sideband?
 
  • #14
Maybe

https://www.nature.com/nature/journal/v464/n7289/full/nature08967.html
Qyantum ground state and single-phonon control of a mechanical resonator
A. D. O’Connell, M. Hofheinz, M. Ansmann, Radoslaw C. Bialczak, M. Lenander, Erik Lucero, M. Neeley, D. Sank, H. Wang, M. Weides, J. Wenner, John M. Martinis & A. N. Cleland

https://arxiv.org/abs/1410.1047
Phonon counting and intensity interferometry of a nanomechanical resonator
Justin D. Cohen, Sean M. Meenehan, Gregory S. MacCabe, Simon Groblacher, Amir H. Safavi-Naeini, Francesco Marsili, Matthew D. Shaw,Oskar Painter
 
  • Like
Likes vanhees71 and Demystifier
  • #15
Plain thermal agitation can be construed as a sea of incoherent phonons, can't it? If so, if you have a molecule that, when excited above a certain threshold, emits a photon, and you maintain a collection of such molecules at a certain temperature such that once in a while the threshold is crossed and a photon is emitted, then it would seem that you have detected a single phonon ‑ namely, the phonon that, added to all others, made the molecule cross that threshold.
 
  • #17
So-called "photon counting" systems do exist, although it does require careful management of your signal to noise ratio. Photon Multiplier Tubes have historically been one method to achieve single photon counting this due to their high gain and high sensitivity.

More reading: Hamamatsu PMT Handbook- Chapter 6: Photon Counting

upload_2017-7-31_14-35-28.png


One modern technology for single photon counting is the "superconducting nanowire single-photon detector," see here:

https://en.wikipedia.org/wiki/Superconducting_nanowire_single-photon_detector
https://www.nist.gov/news-events/news/2013/02/high-efficiency-fastest-single-photon-detector-system
 
  • #18
Andy Resnick said:
(phonons don't have well-defined positions).
I don't see why not. A photon is a quantum of atomic displacement. It is not required that this quantum is in an eigenstate of energy or momentum.
 
  • Like
Likes David Olivier
  • #19
Mech_Engineer said:
So-called "photon counting" systems do exist
This thread is about phonons, not photons.
 
  • #20
jtbell said:
This thread is about phonons, not photons.

Ah. I thought it was about phodons. o0)
 
  • #21
DrDu said:
I don't see why not. A photon is a quantum of atomic displacement. It is not required that this quantum is in an eigenstate of energy or momentum.

Phonons are quantized displacements of a crystal (an ordered array of many atoms); a good discussion is in Coleman's "Introduction to Many Body Physics", chapter 2.4.
 
  • #22
Andy Resnick said:
Phonons are quantized displacements of a crystal (an ordered array of many atoms); a good discussion is in Coleman's "Introduction to Many Body Physics", chapter 2.4.
Yes. I mean, if they aren't eigenstates of energy and crystal momentum, they are time dependent phonons but phonons nevertheless.
 
  • #23
jtbell said:
This thread is about phonons, not photons.

My bad! Carry on... :oops:
 
  • #24
Measurements of the phonon dispersion curves (energy vs. momentum) are very standard in neutron inelastic scattering and to a lesser extent in inelastic x-ray scattering. In these experiments you detect single neutrons and x-ray photons. Each neutron/photon enters the sample will a well-defined energy and momentum (direction), and comes back out with different energy and momentum. The difference is taken up by the phonon, i.e. a phonon is created in the process (or another elementary excitation, e.g. a magnon in a magnetically ordered crystal) . So with each x-ray photon or neutron you measure a single phonon. You need x-rays or thermal neutrons rather than visible light for this because the momentum transfer is on the order of the reciprocal lattice unit.

http://www.nobelprize.org/nobel_prizes/physics/laureates/1994/press.html
http://iopscience.iop.org/article/10.1088/0034-4885/63/2/203/meta

"Thermal diffuse scattering" of x-rays or neutrons is also caused by phonons, but in that case you do not measure the phonon's energy.
 

1. Can single phonons be detected?

Yes, it is possible to detect single phonons using various experimental techniques such as Raman spectroscopy, Brillouin scattering, and cryogenic detectors.

2. What is the significance of detecting single phonons?

Detecting single phonons allows us to study the fundamental properties of materials at the quantum level, which can provide valuable insights into their behavior and potential applications.

3. How sensitive are the methods used to detect single phonons?

The sensitivity of the methods used to detect single phonons depends on the experimental setup and the type of detector used. Some techniques, such as cryogenic detectors, are capable of detecting individual phonons with high sensitivity.

4. Are there any limitations to detecting single phonons?

Yes, there are some limitations to detecting single phonons, such as the presence of background noise and technical challenges in achieving high enough sensitivity. Additionally, some materials may not exhibit clear signals for single phonon detection.

5. What are the potential applications of detecting single phonons?

The ability to detect single phonons has potential applications in fields such as quantum computing, optoelectronics, and materials science. It can also aid in the development of new technologies and materials with unique properties.

Similar threads

  • Atomic and Condensed Matter
Replies
5
Views
883
  • Atomic and Condensed Matter
Replies
1
Views
1K
  • Atomic and Condensed Matter
Replies
7
Views
2K
  • Atomic and Condensed Matter
Replies
7
Views
2K
  • Atomic and Condensed Matter
Replies
1
Views
1K
  • Atomic and Condensed Matter
Replies
4
Views
3K
Replies
11
Views
2K
  • Atomic and Condensed Matter
Replies
9
Views
3K
  • Atomic and Condensed Matter
Replies
4
Views
927
  • Atomic and Condensed Matter
Replies
0
Views
359
Back
Top