Answer by DaftWullie for Density matrix after measurement on density matrix
It is important to emphasise that a density matrix may not be absolute; it represents the state of somebody's knowledge of the system.To see this, consider 3 parties: Alice, Bob and Charlie. Alice...
View ArticleAnswer by ahelwer for Density matrix after measurement on density matrix
So, Bob is given the following state (also called the maximally-mixed state):$\rho = \frac{1}{2}|0\rangle\langle 0| + \frac{1}{2}|1\rangle\langle 1| = \begin{bmatrix} \frac{1}{2} & 0 \\ 0 &...
View ArticleAnswer by Dripto Debroy for Density matrix after measurement on density matrix
So Alice sends Bob a qubit with the density matrix$$\rho = \frac{1}{2}|0\rangle\langle 0| + \frac{1}{2}|1\rangle\langle 1| = \begin{bmatrix} .5 & 0 \\ 0 & .5 \end{bmatrix}$$as you said. (I've...
View ArticleDensity matrix after measurement on density matrix
Let's say Alice wants to send Bob a $|0\rangle$ with probability .5 and $|1\rangle$ also with probability .5. So after a qubit Alice prepares leaves her lab, the system could be represented by the...
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