# 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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### What optical element can you use to implement a square root of NOT gate

How do you implement a square root of NOT gate in an optical quantum computing circuit? What optical element or combination of elements would you use - especially, if you want to manipulate ...
1answer
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### $\sigma$ transition and angular momentum conservation

Suppose we have a box of atomic gas, where each atom has a upper $l=1$ level P and a lower $l=0$ state S. Suppose we then prepare the gas so that all atoms reside in the $l=1, m_z=1$ excited state. ...
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### Transform two-mode squeezed state (TMSS) to its covariance matrix

The two-mode squeezed state can be written as: ${\left| \chi \right\rangle _{AB}} = \sqrt {1 - {\chi ^2}} \sum\nolimits_n^\infty {{\chi ^n}} {\left| n \right\rangle _A}{\left| n \right\rangle _B}$ ...
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### Rotating wave approximation (RWA) in Dicke model

The interaction part of Rabi Hamiltonian is defined as $$H_I = g (a + a^{\dagger})(\sigma_{+}+\sigma_{-})$$ where $g$ is the coupling between atom and the field, the time dependencies of field and ...
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### Dipole moment in the Optical Interaction Hamiltonian [duplicate]

I've got a simple and fundamental question regarding the atom-light interaction Hamiltonian: How do we handle the dipole moment term in this expression? The atom-light interaction Hamiltonian, $H_{AL}$...
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### Relationship between noise spectral density and quantum absorption/emission: I don't understand the derivation

In this paper, on page 57 he performs a calculation that I don't understand. Maybe there is an implicit physical assumption behind so this is why I am asking it here. The context (not necessary to ...
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1answer
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### About two photon interference in nanophotonics

Within the standard model, photons are point particles, i.e., with no spatial distribution. On the other hand, classical electromagnetic modes have field distributions. Suppose there are two different ...
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### Is it possible to laser cool without using spatially-varying magnetic fields and above zero degrees?

As the title says, is it possible to laser cool without generating a weak quadrupolar magnetic field? Also, if I wasn't trying to achieve extremely low temperatures is it possible to use laser cooling ...
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### What does a complex electric field covariance mean?

Assume that one is working with a zero mean state $|\psi\rangle$. The quantum covariance is given by: \text{Cov}(X,Y) = \frac{1}{2}\langle\{A,B\}\rangle-\langle A \rangle\langle B \rangle=\frac{1}{...