# Questions tagged [quantum-information]

Quantum information is the study of the informational content of quantum states. The most common object of study is the "qubit", the information in a two-state quantum system such as spin-1/2 or photon polarization.

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### Grover's Algorithm — Quantum Oracles with different amplitudes

According to https://qiskit.org/textbook/ch-algorithms/grover.html, an oracle creates states like $|\psi⟩=\frac{1}{\sqrt2}|101⟩+|110⟩$, and picks out certain states with equal probability. But if I ...
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### Is partial trace method valid for highly entangled state?

Suppose there are four wires of qubits and the state vector is highly entangled. I want to know the density matrix (or state vector) of wire-$1$ only. In this case, is it available to use partial ...
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### What is an example of a system with non-vanishing topological entanglement entropy at finite temperatures?

In this paper: https://doi.org/10.1088/1367-2630/14/3/033044 it is show that for Kitaev toric code looses topological entanglement entropy over long times if it is thermally opened. What is an example ...
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### Question about DIY Quantum Computer Prototype [closed]

I recently came across these 2 videos on Coursera which show how to build a simple quantum computer that can implement the simplest case of the Deutsch-Jozsa algorithm (which uses only 2 qubits). ...
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### How to specify a general quantum measurement?

I know that a general quantum measurement is described by a set of measurement operators $\{M_j\}$ satisfying the completeness relation $\sum_j M_j^\dagger M_j = 1$ and that the outcome j occurs with ...
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### Quantum Entanglement and transfer of time information, is it possible? [duplicate]

If two particles are quantum entangled...let’s call them particle A and particle B. You measure the state of particle A. At this point, can you know the exact time at which the particle B goes from ...
Fidelity is measure of distance between density operators. it is a measure of the "closeness" of two quantum states, the input state $\rho_{in}$ and the teleported state $\rho_{out}$. where ...