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Is it possible to approximately compile Toffoli using H and CSWAP?

TL;DR: Nope. The triple tensor product of the $+1$ eigenstate of the Hadamard gate is a $+1$ eigenstate of every product of the controlled-SWAP gate and the Hadamard. This is not the case for Toffoli, ...
Adam Zalcman's user avatar
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Is it possible to approximately compile Toffoli using H and CSWAP?

You can exactly implement a Toffoli using CSWAPs catalyzed by a singlet state: The singlet state is the -1 eigenstate of the swap gate, and you can get phase kickback from a swap by using cswap, so ...
Craig Gidney's user avatar
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