Questions tagged [quantum-optics]
A research field within general optical physics concerned with light and its material interaction: where light is modelled by full quantum mechanical description.
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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 ...
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Why do lasers require mirror at the ends?
Laser uses mirrors to reflect photons in order to stimulate atoms to emit photons, but why this is so?. I mean, why does a photon stimulate atoms to produce more photons? If a photon made an atom to ...
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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 ...
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Why doesn't there exist a wave function for a photon whereas it exists for an electron?
A photon is an excitation or a particle created in the electromagnetic field whereas an electron is an excitation or a particle created in the "electron" field, according to second-quantization.
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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 ...
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Does spontaneous emission actually emit in a random direction, or is it measured in a random direction?
When an excited state couples to the vacuum, it has an infinite number of directions of the quantized electromagnetic field to couple to. Does it evolve into a superposition of all those directions at ...
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What causes atoms to have their specific colors?
I understand that light (color) is part of the electromagnetic spectrum, and that it depends on what wavelengths are reflected/absorbed. Though what property of an individual atom gives it its color? ...
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Phase added on reflection at a beam splitter?
If we have light of a particular phase that is incident on a beam splitter, I assume the transmitted beam undergoes no phase change. But I thought that the reflected beam would undergo a phase change ...
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What is the orbital angular momentum (OAM) of individual photons?
Update @ 21.01.2018
People investigate and talk about orbital angular momentum (OAM) of photons. For example, see this well-cited paper here and the PRL here. The latter starts with the remark
It ...
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Wave function of a photon?
Consider a single photon. Since it is not possible to create a photon with a certain frequency it can be characterized by a normalized frequency distribution $f(\nu)$ that is peaked around some mean ...
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How does a laser emit light in a coherent state?
Lasers work by stimulated emission of atomic transitions. Stimulated emission produces two photons which, because the particle number is well-defined, projects the field into a Fock state. However, it ...
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Book Recommendation: Quantum optics
Could you suggest me a list of books for understanding Quantum Optics for students who have studied Introductory Q.M. (such as Griffiths).
It would be grateful if you distinguish between readable one ...
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What IS reflection?
How does quantum electrodynamics actually explain HOW reflection occurs on a microscopic scale?
Note that Feynman's QED lecture series/book is not sufficient, as he only assumes that light DOES ...
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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 ...
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Photons with half integer angular momentum - what's happening?
I have just read this article - what is happening?
Analysing these beams within the theory of quantum mechanics they predicted that the angular momentum of the photon would be half-integer, and ...
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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 ...
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What does a photon emitted by an atom "look" like?
Consider the emission of a photon when an atom decays from an excited state to its ground state. In most cases, this emitted photon is depicted as a small wave-packet being expelled by the atom in a ...
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What is the Wigner function of $|n\rangle\langle m|$?
I have been searching in the literature for the Wigner function of $|n \rangle \langle m|$. For $n=m$ it can be found in page 120 of Barnett and Radmore's Methods in Theoretical Quantum Optics and it ...
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What does it mean to Fourier transform a ladder operator (in the input-output formalism)?
I am currently trying to get my head around the input-output formalism.
In describing the input-output formalism (link) , Gardiner and Collett take ladder operators in the Heisenberg picture and ...
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Eigenstates of the creation operator
We know that coherent states $\vert\alpha\rangle$ are eigenvectors of the annihilation operator $\hat{a}$, i.e.
$$
\hat{a} \vert\alpha\rangle = \alpha \vert\alpha\rangle
$$
while the creation operator ...
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Gaining some intuition for thermal sources producing photon bunching
This is a very easy question: I'm in need of some intuition on the fact that, e.g. thermal sources, produce bunched photons. It is very easy to "undertand", without any quantum mechanics, why single ...
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Why is laser light described by a coherent state?
This is a follow-up to this recent answer by Wouter to this related question from 2015, and a comment by Emilio Pisanty underneath.
I have read the papers by Mølmer, Bartlett et al., Wiseman, and ...
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Lasing in a 2-Level system?
What exactly is the difference between 2-Level, 3-Level and 4-Level systems? Why can we not achieve stimulated emission in a two-level system using optical pumping?
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Why does an image only form where light rays coming from a single point get reflected or refracted and converge to a common point?
I am a high school student and I have read many books and information on the internet about concept of object and image in optics. They all say that where reflected/refracted rays intersect they form ...
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Meaning of "intensity" in the optical Kerr effect in optical quantum computation
Kerr media, or mediums displaying the optical Kerr effect, are used in some optical quantum computers - on Chuang and Nielsen's Quantum Computing and Quantum Information, pgs. 289 - 290, it says,
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Understanding the relationship between Phase Space Distributions (Wigner vs Glauber-Sudarshan P vs Husimi Q)
I am moving into a new field and after thorough literature research need help appreciating what is out there.
In the continuos variable formulation of optical state space.
(Quantum mechanical/Optical) ...
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Output of a beamsplitter with photon number (Fock) state inputs
Given a beamsplitter drawn below, where $\hat{a}$ and $\hat{b}$ are input modal annihilation operators, transmissivity is $\tau\in[0,1]$, and output modal annihilation operators are $\hat{c}=\sqrt{\...
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Are photons inside the media massive? If yes, why there is no Meissner effect?
We all know the photon in vacuum travels with speed $c$, hence its rest mass has to be 0. In the media the light speed $v<c$. Then the photon renormalized by the medium (call it "quasi-photon&...
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Derivation of $P$ representation of the thermal density operator
I'm trying to derive the P representation for the thermal state
$$
\rho = \sum_{n=0}^\infty \frac{\mathrm{e}^{-\beta \omega n}}{Z} |n\rangle \langle n |
$$
where $\beta$ is the inverse temperature, $...
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What are the 'types' of parametric down conversion?
I'm looking at photon entanglement, and everywhere in the literature there's a reference to 'type-II' parametric down conversion as a source of entangled photon pairs. I know what parametric down ...
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'size' of a photon
What's the smallest aperture a photon can pass through? I mean with no transmission at all.
I'm pretty sure I saw long ago an experiment when they were reducing the size of a hole in a gold film and ...
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How to understand the completeness relation for coherent states in the "coherent space"?
In a set of notes it is stated that: Given coherent states of a harmonic oscillator $$| \alpha \rangle = \pi^{-\frac{1}{2}} \text{exp}(-\frac{1}{2}|\alpha|^2)\sum_{n = 0}^{\infty} \frac{\alpha^n}{(n!)^...
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Obtain the Lagrangian from the system of coupled equation [closed]
In this particular paper,
"Interaction between a moving mirror and radiation pressure:
A Hamiltonian formulation" by C.K.Law, PhysRevA.51.2537
\begin{equation}
\ddot{Q}_{k}=-\omega^{2}_{k}Q_{k}+2\...
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Photons in coulomb field
Does coulomb field contain photons?
As 1 THz and 1 kHz fields differ only in frequency,
how does 0 Hz field differ from them?
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How does the energy of a single photon manifest itself as the frequency of the classical EM wave?
We know that the energy of the photon is given by $\hbar\omega$ and it so happens that this exact $\omega$ is the frequency we would obtain from the many photon EM wave. How does one relate the two?
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Single slit diffraction from Feynman's rotating amplitudes ("Little Arrows")
In Feynman's NZ lectures (and consequent book) “QED – The Strange Theory of Light and Matter”, he gives a model for optics.
He describes a probability amplitude for a photon to be detected after being ...
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Quantum and non-equilibrium properties of the radiation, emitted by "thermal light sources"
Free photon gas
Let us consider different thermal light sources, such as the Sun, an incandescent lamp, or a fluorescent bulb. In elementary quantum mechanics and statistical physics one describes the ...
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Time duration for pulse of single electron viewed as a wave
Electron as an example has a de Broglie wavelength and could diffract.
If it has a single wavelength the time extent of the particle's pulse duration would be infinite ..
If it carries a broadband ...
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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 ...
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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 ...
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Stimulated emission and No-cloning theorem
I have a little trouble with the simulated emission. I know of the no-cloning theorem which states that it is not possible to duplicate any state.
One the other hand, I know about the stimulated ...
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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 ...
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Informational capacity of qubits and photons
How much information is contained in one qubit?
A qubit is defined in Wikipedia as $a\left|0\right> +b\left|1\right>$, where a and b are complex numbers subject to $a^2 + b^2 = 1$.
One complex ...
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Why is the quantum Venn diagram paradox considered a paradox?
I've just watched this video on YouTube called Bell's Theorem: The Quantum Venn Diagram Paradox
I don't quite understand why it is considered a paradox
At 0:30, he says that as you rotate 2 ...
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Why does stimulated emission not contribute to linewidth?
The rough quantum mechanical explanation for linewidth is that the lifetime $\tau$ of an excited level is associated with an uncertainty $\Delta E$ in its energy satisfying $$\Delta E\tau=\hbar$$ and ...
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Why doesn't the momentum exchange (or lack thereof) between photon and beam-splitter destroy the interference?
I have a question (my very first here) related to 50/50 beam splitters as used in the Mach-Zehnder interferometers (see for example the Wikipedia page).
Let's concentrate on the input beam splitter: ...
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Why does classical light always result in super-Poissonian statistics?
It is a well-known result that classical light (which I take here to mean mixtures of coherent states) cannot produce sub-Poissonian photon-counting statistics, with a single beam of coherent light ...
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What is the current consensus on a well-behaving 'Quantum Phase Operator' (in Fock-state basis)?
I'm interested in a quantum operator that returns the phase of some quantized light in the Fock state basis.
That is, if I perform (in a density matrix picture) the expected value of this 'phase ...
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The definition of a $\pi$ polarized photon?
I am looking at the definition of $\sigma^\pm$ and $\pi$ polarized photons (in the context of atomic transitions), however I have seem to come across two (both seen in numerous sources surrounding the ...
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Find the Bogoliubov transformation $b=SaS^\dagger$ induced by the squeezed operator
A definition a bogoliubov transformation is defined as $$b=ua+va^\dagger~,~ b^\dagger=u^*a^\dagger+v^*a$$
But, using squeeze operator $$S=\exp{\left[\frac{1}{2}(z (a^\dagger)^2-z^*a^2)\right]}$$ we ...
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