New answers tagged density-matrix
6
votes
Accepted
Finding the eigenvalues of a qutrit state
Maybe you forgot about the coefficient $\frac{1}{\sqrt{2}}$. The correct reduced density matrix is $$\frac12 (\left|1\right>\left<1\right| + \left|2\right>\left<2\right|)$$
- 208
2
votes
How to find density matrix of 3 qubit W state?
We can get the density matrix $\rho$ for a pure state $|\psi\rangle$ using
$$\rho=|\psi\rangle\langle\psi|$$
And to write $\rho$ using the Pauli basis $\left\{ P_i \right\}$,
$$\rho = \sum_{i=0}^N \...
- 9,132
4
votes
Accepted
Is possible to write a separable state as a finite or countable infinite sum of product states?
Yes, you can always write an integral of separable states as a (finite) convex combination of product states, owing to the fact that the set of separable states is compact.
A quick way to see this is ...
- 5,158
1
vote
QISKIT: ValueError: too many subscripts in einsum DensityMatrix()
Try to transpile your circuit into 1- and 2-qubit gates:
qc = transpile(qc, basis_gates=['cx', 'u'])
rho = DensityMatrix(qc)
This issue happens because Numpy ...
- 9,132
2
votes
Accepted
Derivation of Choi-Jamiolkowski isomorphism
It's easier to work with matrix units $E_{ij} = |i\rangle \langle j|$. In particular, we have
$$
|\Omega\rangle \langle \Omega| = \sum_{i,j}c_i\overline{c_j} E_{ij} \otimes E_{ij}\tag{1}\,.
$$
The ...
- 6,721
1
vote
Accepted
How to get the Kraus operator $M_0=\sqrt{1-p}\, I$ for the depolarizing channel, from its isometric representation?
The unitary representation specifies how the isometry $U$ acts on pure states. The channel $\Phi$ is related to $U$ by $\Phi(\rho)=\operatorname{tr}_E[U\rho U^\dagger]$. Notice that on pure states ...
glS♦
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