generate maximally mixed state

ITensor Julia Questions
1

Hi,

Is there a way to generate a mixed state of N qubits such that the initial density operator of the total system is \begin{pmatrix} 1/2 &0\\0 &1/2\end{pmatrix}^{\otimes N}?

Thanks

2

You could use the following:

julia> using ITensors

julia> n = 4
4

julia> s = siteinds("Qubit", n);

julia> rho = MPO(s, "Id");

julia> rho = rho ./ 2;

The syntax rho = rho ./ 2 divides each tensor in the MPO by 2 using Julia’s broadcasting syntax.

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3

Hi, guys I have a further question. How to realize the time evolution of MPO? I am thinking the case that P_1U_n\dots U_1 \rho U_1^{\dagger}\dots U_n^{\dagger}P_1 where U is some unitary operator and P represents projective measurement.

4

Oh I just find this https://github.com/ITensor/ITensors.jl/blob/main/examples/gate_evolution/mpo_gate_evolution.jl, it may be what I need.

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