All Questions
Tagged with informationquantum-mechanics
87 questions
2votes
2answers
127views
How does writing and erasing memory change entropy?
Picture is from here I think I have serious misunderstanding of the topic, and hope that somebody could point out where the mistakes in my reasoning are. Having looked through many other related posts,...
0votes
2answers
79views
Why is it possible to tell with certainty whether a qubit is disturbed but not whether it is intact?
Consider a qubit ${\mid}\psi\rangle = a{\mid}0\rangle + b{\mid}1\rangle$. Assume we know what $a$ and $b$ are. It then goes through a black box and we want to determine in a single shot whether it was ...
- 1,425
1vote
0answers
55views
In the Bekenstein bound, is $E$ and/or $R$ meant to be a strict upper bound or an average? (how to fit with position/momentum uncertainty?)
In the Bekenstein bound, $S\le2\pi R E/\hbar c$, where $E$ is the energy of the system (including mass energy etc.), and $R$ is the radius of a ball containing the system, which of these is strict (if ...
- 11
3votes
1answer
89views
What is the meaning of divergent quantum fisher information?
I've recently come across this example, and it has me confused. I've computed the quantum fisher information (QFI) for a qubit initialized along the $\hat x$ axis ($|\uparrow_x\rangle=\frac1{\sqrt{2}}\...
- 107
-4votes
1answer
106views
Transmitting Data faster than the speed of light using entangled particles [duplicate]
If we have a pair of super-asymmetrical entangled particles, and move them a light year away so that they retain their quantum entanglement, and we set a clockwise spin (or vertical polarization) as 0 ...
- 11
0votes
1answer
71views
Are all types of noise a result of lack of complete knowledge about the given system? What does this say about the physicality about information?
I am currently studying the basics of quantum information theory. When we study a system (classical or quantum), any undesirable influence out of our control is usually referred to as noise, and this ...
2votes
1answer
144views
Proving that a positive partial transpose (PPT) state is non-distillable
I am attempting to prove the following statement: A positive partial transpose (PPT) state cannot be distilled. I would like to do so using the following facts: Let $\rho$ represent a bipartite ...
- 21
2votes
1answer
92views
Fisher information of parametric channel
Suppose $\Phi_\theta$ is a quantum channel whose action can be written for any state $\rho\in \mathcal S(\mathcal H_S)$ in the Stinespring representation as $\Phi_\theta(\rho)= \text{Tr}_E(U_\theta (\...
2votes
0answers
43views
Is the optimal POVM of a mixed state the same as the optimal POVM of the pure states in its ensemble?
If I have a mixed state, where each pure state in the ensemble has the same optimal POVM (by optimal I mean POVM for which the classical Fisher information is the same as the quantum Fisher ...
0votes
0answers
186views
The difference between classical and quantum entropies
The von Neumann entropy $-\mathrm{Tr}(\rho\ \log\rho)$ of a quantum thermal state with $\rho=\frac{1}{Z}e^{-\beta H}$ gives the thermal entropy, see e.g. this question. The von Neumann entropy is a ...
- 165
0votes
0answers
26views
Communication via entanglement [duplicate]
For years now i have in my haed a thought experiment for information exchange via quantum entanglement. And i am aware that something must be wrong with it but i can't figure out what it is. The ...
-1votes
1answer
132views
Faster than light communication by entangled photons [duplicate]
Faster than light communication is not possible. If I measure the polarization of an entangled photon and it turns out to be right circularly polarized. In that instant, dont I know that someone ...
0votes
0answers
25views
How can entanglement entropy be quantified between lattices of differing structures?
Suppose there are two 1 dimensional particle lattices, both with differing distances between particles and not necessarily the same number of particles. Each particle exists in a superposition of spin ...
- 23
8votes
2answers
684views
Accounting for computation time in Counterfactual Computers
After researching some stuff about Turing Machines and Automaton Theory I stumbled upon the concept of "counterfactual computers". Having little experience with quantum physics (and usually ...
- 337
1vote
0answers
54views
Is my "Tentative Note on the origin and the evolution of information in the universe" correct? [closed]
As a teacher of physics I got many questions asked by my students when aboarding the subject of information in quantum mechanics and the content of information in the universe. Based on my reading of ...
- 1,006
