# Questions tagged [density-operator]

The density operator describes a quantum system in an (in general mixed) state.

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### Double slits experiment: how does the which-way entropy vary with the distance between slits and screen?

When the screen is just behind the slits we have perfect which way information. The entropy is log 2. It decreases if I place the screen in the Fresnel region (not to far). It decreases much more in ...
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### Shake water and seed oil: color and density

These days I am spraying the leaves of my garden, to prevent insects, mixing strongly water and soya oil. The color has become all white. Soy oil has a relative density of $0.915 \div 0.925$ kg/dm$^3$...
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### Calculate probability of a state after depolarization

Let's say I have a particle in the quantum state $|+\rangle = \frac{1}{\sqrt{2}}(|0\rangle + |1\rangle)$, represented as a density operator (1st matrix) that went through a depolarizing chanel (2nd ...
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### Baker–Campbell–Hausdorff and Gaussian density operators for fermions

I'm trying to understand a passage from the paper "Gaussian operator bases for correlated fermions", J. F. Corney and P. D. Drummond (https://arxiv.org/abs/quant-ph/0511007), specifically ...