# Tag Info

## New answers tagged density-matrix

### State tomography with Pauli basis measurements for a high number of qubits

32 qubits give you a Hilbert space dimension of $d=2^{32} = 4\,294\,967\,296$. A recent paper has done tomography of $d=20$ dimensional state, with the highest infidelities for tomography made so far ...
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### Is there an expression for the partial trace of a vectorized density matrix?

Let $\rho$ be a bipartite linear operator (it doesn't really matter here whether it's Hermitian, positive, or anything else). Denote with $\operatorname{vec}(\rho)$ its vectorisation. The partial ...
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### Action of a channel on an "unphysical" state

A quantum channel sends states to states, which are positive semidefinite matrices. But it is a linear map. There's no problem in extending its action to all matrices by linearity, since every matrix ...
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### How simulation of noisy quantum circuits is done in Qiskit using the statevector method

Trajectory - the simulator draws in random (probability depends on the quantum state and noise) one of the Kraus operators, applies it, and normalizes the state. For a large number of shots, if you ...

### CNOT gate an elementary example of a single qubit quantum operation

My understanding about CNOT gate is that the control qubit remains the same and only the target qubit flips iff the control qubit state is $|1\rangle$. This is a reasonable intuition but it is ...
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### CNOT gate an elementary example of a single qubit quantum operation

First let's clarify the configuration of the system described in the book - Given a principal system in inital state $\rho$ and the environement being simplified to a system in an initial state \$|0\...
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