Tuesday, February 2, 2016

functional analysis - A linear map from mathbbCnotimesoverlinemathbbCn to Mn(mathbbC)

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I am trying to establish some properties of the linear map: T:\mathbb{C}^n \otimes \overline{\mathbb{C}^n} \to M_n(\mathbb{C}) given by: T(\ket{i} \otimes \ket{j}) = \ket{i}\bra{j} \text{ , } 0 \leq i,j \leq n-1.




Where \otimes denotes the tensor product, \overline{\mathbb{C}^n} is the conjugate space of the complex (finite) Hilbert space \mathbb{C}^n, and M_n(\mathbb{C}) is the set of n\times n matrices over \mathbb{C}.



I want to show the following:




(i) T is a bijection that preserves inner products (under the
Hilbert-Schmidt inner product on M_n(\mathbb{C})



(ii) T(\ket{\psi}\otimes\ket{\varphi} = \ket{\psi}\bra{\varphi} for
every \ket{\psi}, \ket{\varphi} \in \mathbb{C}^n.





I think part of my trouble is figuring out the Dirac notation / how the outer product works. I'm not sure exactly what \ket{i}\bra{j} looks like as a matrix (obviously it's a matrix in M_n(\mathbb{C}) but I'm not quite sure what the entries look like).



Also, I think part (ii) of the question is an immediate consequence from the fact that T is a linear, inner product preserving bijection, but I'm a bit confused about why \ket{\varphi} is now coming from \mathbb{C}^n rather than \overline{\mathbb{C}^n}.



Any help is appreciated.

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