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arXiv · 1910.05515

Mutually unbiased bases containing a complex Hadamard matrix of Schmidt rank three

Mengyao Hu·Yize Sun·Lin Chen
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Abstract

Constructing four six-dimensional mutually unbiased bases (MUBs) is an open problem in quantum physics and measurement. We investigate the existence of four MUBs including the identity, and a complex Hadamard matrix (CHM) of Schmidt rank three. The CHM is equivalent to a controlled unitary operation on the qubit-qutrit system via local unitary transformation $I_2\otimes V$ and $I_2\otimes W$. We show that $V$ and $W$ have no zero entry, and apply it to exclude examples as members of MUBs. We further show that the maximum of entangling power of controlled unitary operation is $\log_2 3$ ebits. We derive the condition under which the maximum is achieved, and construct concrete examples. Our results describe the phenomenon that if a CHM of Schmidt rank three belongs to an MUB then its entangling power may not reach the maximum.

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Mengyao Hu, Yize Sun, Lin Chen. 2019-10-12. Mutually unbiased bases containing a complex Hadamard matrix of Schmidt rank three. https://doi.org/10.1098/rspa.2019.0754

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