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 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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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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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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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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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 ...
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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 ...
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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 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 ...
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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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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 ...
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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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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}^\...
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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 ...
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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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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 ...
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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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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 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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Unambiguous distinguishing of quantum states by local measurement
Let's have two orthogonal n-particle quantum states: $|\psi \rangle$ and $|\phi \rangle$. In theory it is always possible to make an unambiguous measurement.
However, things get complicated when one ...
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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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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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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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Reference request: Susskind-Glogower original paper
I'm trying to find Susskind and Glogower's original paper,
L. Susskind and J. Glogower. Quantum mechanical phase and time operator. Physics 1 (1964) 49-61
where they propose their exponential and ...
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What is the experimental evidence for a quantized EM field?
I've recently been trying to understand on a deeper level what is the physical meaning or existance of photons, and relatedly, what is the experimental verification of their existance. We all learn ...
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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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Countable basis of coherent states used to express coherent states
Let $|\alpha \rangle$ be coherent state in Fock space. According to the paper "Coherent-state representation for the photon density operator" by Cahill (Phys. Rev. 138, B1566 (1965), §VII), every ...
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Nonlinear optics as gauge theory
the widely used approach to nonlinear optics is a Taylor expansion of the dielectric displacement field $\mathbf{D} = \epsilon_0\cdot\mathbf{E} + \mathbf{P}$ in a Fourier representation of the ...
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Which of these theories on why light slows in media are true?
This question is similar to previously asked questions, but the responses to them are confusing and I think it may be better covered by listing out all the potential answers for clarity.
It's a ...
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What will happen to an entangled pair of photons if one of them is absorbed and remitted by an atom?
Imagine if I have an entangled photon pair in linear polarisation, let them be named photon A and photon B, and if photon A is absorbed by an atom and then re-emitted what would be the state of photon ...
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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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Why don't atoms emit more than one photon during an energy level transition?
If you look at the emission spectrum of an atom, there are sharp lines corresponding to the different energy level transitions. That's because the single photon emitted during each transition carries ...
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Group theory and quantum optics
This is a question about application of group theory to physics.
The starting point is the group $SU(n)$. I have a representation $R$ of $SU(n)$ that takes values on the unitary group on an infinite ...
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Is it possible to create a mirror that redshifts light?
Mirrors are able to reflect light but are not perfect and after a number of reflections, light loses intensity.
However I wonder, during the reflection by a different type of mirror, could the light ...
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Can people create single photon in the laboratory?
Can a single photon be created in the laboratory? How do people make sure that they have really created a single photon?
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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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Why is Dirac's Phase Operator Non-Hermitian?
I'm self-studying Gerry and Knight. To prove Dirac's phase operator is non-existent, the book makes the following argument.
The conventions used are as follows: $\hat{n}$ is the number operator, $\hat{...
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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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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 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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How much can we currently squeeze light?
In quantum optics, the single-mode squeezed vacuum is the state
$$\hat S(z)|0\rangle=\exp\left(\frac{1}{2}\left(z^*\hat a_{\mathbf k}^2-z\hat a_{\mathbf k}^{\dagger 2}\right)\right)|0\rangle$$
where $...
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The requirement of a relatively weak coupling for the application of the rotating wave approximation to obtain the Jaynes-Cummings model
In order to obtain the Jaynes-Cummings Hamiltonian, the RWA is applied to the Rabi Hamiltonian:
$$H=\frac{1}{2}\hbar\omega_0 \sigma_z+\hbar\omega \hat{a}^{\dagger}\hat{a}+\hbar g(\sigma_{+}+\sigma_{-})...
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What is the "direction" of the transition dipole moment? (Understanding Eq. 9.29, Charge and Energy Transfer 3rd Ed, May & Kuhn)
For a real vector $\mathbf{r}$, the direction is given by: $\hat{\mathbf{n}}=\mathbf{r}/\left|\mathbf{r}\right|$.
The transition dipole moment is a complex vector. How do you define its direction?
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How can one recover the classical frequency-modulation Bessel sidebands from a quantum emitter in a harmonic well?
Consider an atom that emits at frequency $\omega_0$ that's located at a position $x$ that moves under the influence of a harmonic oscillator at frequency $\nu$. In both classical and quantum physics, ...
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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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Computer game with quantum optics/ information [closed]
Is there a computer game using principles of quantum optics or quantum information?
By game I don't mean just a simulation or an interactive course, but something that can be played in an enjoyable ...
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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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Which qubit states are accessible with linear optics operations?
Given a quantum state of $n$ qubits, and being restricted to linear optics (that is, the output annihilation operators are linear combinations of the input annihilation operators):
Which states are ...
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What is the length of a photon?
Some questions that look kind of similar have been asked before, and I find the answers quite confusing. I intend to ask this question in a way that clearly shows what I'm asking.
Imagine the ...
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Quantum shot-noise and the fluctuation dissipation theorem
Classically, shot noise observed in the signal generated by a laser incident on a photodiode is explained as being due to the quantization of light into photons, giving rise to a Poisson process. In ...
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Runge Kutta Method for a Lindblad Equation
I am solving a Lindblad equation for a dissipative Harmonic Oscillator.
My Hamiltonian is time dependent,
My Lindblad Equation can be written as
\begin{equation}
\frac{d\rho}{dt}=\frac{[H(t),\rho]}{i\...
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