A research field within general optical physics concerned with light and its material interaction: where light is modelled by full quantum mechanical description.
Questions tagged [quantum-optics]
1316 questions
53
votes
5 answers
Why doesn't a typical beam splitter cause a photon to decohere?
In many experiments in quantum mechanics, a single photon is sent to a mirror which it passes through or bounces off with 50% probability, then the same for some more similar mirrors, and at the end we get interference between the various paths.…
Mark Eichenlaub
- 53,961
48
votes
4 answers
Rigorous justification for rotating wave approximation
Whenever I have encountered the rotating wave approximation, I have seen "the terms that we are neglecting correspond to rapid oscillations in the interaction Hamiltonian, so they will average to 0 in a reasonable time scale" as the justification…
Abel Molina
- 792
43
votes
8 answers
Does a photon interfere only with itself?
I sometimes hear statements like:
Quantum-mechanically, an interference pattern occurs due to quantum interference of the wavefunction of a photon. The wavefunction of a single photon only interferes with itself. Different photons (for example from…
Kostya
- 20,288
42
votes
4 answers
Fourier transform paradox(?) of a wave packet
Assume you have a near perfect monochromatic red laser light. The Fourier transform of the laser light is a delta function peaked at the frequency of the light.
Now assume someone places a shutter on the path of the moving light, cutting off a wave…
Normie
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31
votes
4 answers
Why doesn't the phase operator exist?
In many articles about quantum optics, the phase-number uncertainty relation $$\Delta \phi \Delta n \ge 1$$ has been mentioned and used as a heuristic argument, but they say that the phase-number uncertainty relation does not exist in a strict…
Veteran
- 675
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29
votes
9 answers
Are quantum effects significant in lens design?
Over on Photography, a question was asked as to why (camera) lenses are always cylindrical. Paraphrasing slightly, one of the answers and follow-up comments asserted that quantum effects are significant and that you need to understand QED in order…
Philip Kendall
- 495
29
votes
1 answer
Why is UV light visible when reflected off paper?
I was carrying out a photoelectric effect experiment when I realised that the $365$ nm line in the mercury spectrum was surprisingly visible when shone onto a piece of paper. This lies in the UV spectrum, and it is not visible directly. However, I…
Harambe
- 510
25
votes
9 answers
Why does light travel in a straight line if the uncertainty principle is true?
I've asked this on different websites and never gotten an answer that a layperson can understand. Most people just say that light does not have a trajectory and then they do some hand waving. If light does not have a trajectory, then how do we…
aa bb
- 361
25
votes
5 answers
Why do coherent states have Poisson number distribution?
In quantum mechanics, a coherent state of a quantum harmonic oscillator (QHO) is an eigenstate of the lowering operator. Expanding in the number basis, we find that the number of photons in a coherent state follows a Poisson distribution.
Is there…
knzhou
- 107,105
23
votes
3 answers
How is squeezed light produced?
Ordinary laser light has equal uncertainty in phase and amplitude. When an otherwise perfect laser beam is incident onto a photodetector, the uncertainty in photon number will produce shot noise with poisson statistics.
However, laser light may be…
nibot
- 9,691
21
votes
1 answer
How can I write a Gaussian state as a squeezed, displaced thermal state?
I would like to write a Gaussian state with density matrix $\rho$ (single mode) as a squeezed, displaced thermal state:
\begin{gather}
\rho = \hat{S}(\zeta) \hat{D}(\alpha) \rho_{\bar{n}} \hat{D}^\dagger(\alpha) \hat{S}^\dagger(\zeta)…
P. Plowman
- 367
20
votes
7 answers
Are coherent states of light 'classical' or 'quantum'?
Coherent states of light, defined as
$$|\alpha\rangle=e^{-\frac{|\alpha|^2}{2}}\sum_{n=0}^\infty \frac{\alpha^n}{\sqrt{n!}}|n\rangle
$$
for a given complex number $\alpha$ and where $|n\rangle$ is a Fock state with $n$ photons, are usually referred…
Juan Miguel Arrazola
- 1,404
19
votes
7 answers
Optical equivalent of a superconductor
Is there some material state that can propagate light indefinitely without dissipation or absorption, like superconductors are able to transmit current indefinitely?
If not, then the question is, why not? would some fundamental principle being…
lurscher
- 14,933
19
votes
2 answers
What is $g^{(2)}$ in the context of quantum optics? And how is it calculated?
I have been studying research papers on Quantum Optics and non-linear optics. I frequently come across the $g^{(2)}$ value. What does it signify? What is its importance? How to calculate it? And do the calculation methods vary? If yes, what…
AKSHIT KUMAR
- 379
18
votes
3 answers
Quantum memories: What are they?
Searching the literature for the term "quantum memory" seems to bring up results from two different communities.
On the one hand there are quantum opticians, who see a quantum memory as something used to absorb a photon and store its quantum state…
Matthew Matic
- 695