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# Questions tagged [density-matrix]

For questions about density matrices and related concepts and ideas, e.g. procedures for computing properties of quantum states from their density matrices.

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### Can we use a Werner state for quantum teleportation? [duplicate]

Some background: The quantum teleportation protocol requires first that Alice and Bob share an entangled state, say a Bell state $|\psi^{+}\rangle_{AB}$. There is another state $|\psi\rangle_{A'}$ to ...
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### How do I find the reduced density matrix of a system where two people share one qubit and have one qubit of their own?

I have the following problem and have attempted to find a solution to it, but to no avail. Alice and Bob have one qubit each, say $|\psi\rangle$ with Alice and $|\phi\rangle$ with Bob. They also share ...
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### Can density matrices of multipartite systems always be written as product states?

suppose the density matrix $\rho_{ABC}$ with the subsystems {A,B,C} can we write $\rho_{ABC}$ as below? $\rho_{ABC}=\rho_A \otimes \rho_B \otimes \rho_C$ if the answer is yes please share a ...
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### Tf.einsum vs matmul for computing density matrix from a set of Cholesky decomposed matrices

I am trying to construct a density matrix of shape 256x256 from a set of T matrices. These T matrices are all Cholesky-decomposed matrices. But I am not sure if the ...
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### Is it possible to apply a quantum gate to a density marix from a partial trace?

To apply a gate(matrix) to a 2 qubit partial trace(4x4 matrix) I have this function: ...
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### Operator qubit ordering not matching circuit qubit ordering

I tried constructing a cx gate manually using tensor products and one using QuantumCircuit in qiskit followed by converting it ...
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