# What is Fidelity: Definition and 11 Discussions

Fidelity is the quality of faithfulness or loyalty. Its original meaning regarded duty in a broader sense than the related concept of fealty. Both derive from the Latin word fidēlis, meaning "faithful or loyal". In the City of London financial markets it has traditionally been used in the sense encompassed in the motto "My word is my bond".

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1. ### I Is time continuous or discrete in quantum physics?

I was working on plotting fidelity with time for two quantum states. First I used discrete time( t= 0,1,2,3...etc) to plot my fidelity. I got constant fidelity as 1 with continuous value of time. Next I used discrete set of values ( t=0 °,30 °,60 °,90 °). Here I saw my fidelity decreases and...
2. ### A Max Fidelity at $$F=|\langle\psi|\phi\rangle|^2$$

$$F =|\langle\psi|\phi \rangle|^2$$ $$|\psi\rangle=|\alpha\rangle|0\rangle$$ $$|\phi\rangle= |\cos(t)\alpha\rangle|i\alpha\sin(t)\rangle$$ $$F=|(|\langle\alpha|\langle 0|)(|\cos(t)\alpha\rangle|i\alpha\sin(t)\rangle)|^2$$ Now simplifying $$\langle\alpha|\cos(t)\alpha\rangle$$...
3. ### A Fidelity for quantum state at t=0

fidelity for pure state with respect to t=0 is 1. My teacher told me this. But I am not getting this. This is my detailed question the initial state(t=0)##|\psi\rangle=|\alpha\rangle|0\rangle## the final state (t) ##|\chi\rangle= |i\alpha\sin(t)\rangle|cos(t)\alpha\rangle## Fidelity between the...
4. ### A Fidelity between initial and final states

I have a state |0>|alpha>. Now I want to evolve this state at any time t and find the fidelity between the initial and final states. Any ideas how to do that? My main problem is that I don't know how to evolve this state.
5. ### I PROOF: Quantum Fidelity with pure states

Hi, I'm currently working on showing the relation of quantum fidelity: The quantum “fidelity” between two pure states ρ1 = |ψ1⟩⟨ψ1| and ρ2 = |ψ2⟩⟨ψ2| is given by |⟨ψ1|ψ2⟩|^2. Show that this quantity may be written as Tr(ρ1ρ2). I've been following the wikipedia page on fidelity but can't...
6. ### Fidelity between a pure state and an arbitrary state

\Homework Statement Show that the Fidelity between one pure state |\Psi\rangle and one arbitrary state \rho is given by F(|\Psi\rangle , \rho)=\sqrt{\langle\Psi|\rho|\Psi\rangle} . Homework Equations The quantum mechanical fidelity is defined as \begin{equation*}...
7. ### Can a Free 2 Axis Gyro Model Account for Contact with a Stop?

I want to model a free 2 axis free gyro. I used to have a very detailed model, but cannot find it. It was cross coupled, and included many disturbance torques. All I am looking for is a great source on this topic. Thanks! Mike
8. ### Formalisms (in fidelity calculation for quantum teleportation)

Hi, I am trying to read a paper about quantum teleportation and got stuck with calculating the fidelity of the mixed(noisy) channel. Fidelity F := < \Phi^{(-)}_{12} | \rho_{1} \otimes \rho_{23} | \Phi^{(-)}_{12} > where \rho_{1} = | \phi_{1} > < \phi_{1} | and \rho_{23} = t |...
9. ### Best Teleportation Fidelity to date

Hello all, I am looking for references to experimentally measured quantum teleporation fidelities. In particular, I am trying to find what is the best fidelity to date. So far I have: Bouwmeester et al., Nature v390, p575 (1997), 0.70±0.3 (with polarization-encoded qubits, before subtracting...
10. ### What does it mean by having a quantum fidelity of 0.85?

What does it mean by having a quantum fidelity of 0.85?
11. ### Can Slow Glass or Optical Black Holes Be Used for Storing Photons?

In general teleportation protocol, an entagled pair is used as a source for teleporting an unknown quantum state and the fidelity, which depends on the source characteristics, is defined as the resemblance of final state to the teleportated state . Suppose we have given a density matrix for an...