| 研究実績の概要 |
This academic year we worked on various problems related to quantum algorithms and post-quantum cryptography.
We investigated the problem of graph coloring by distributed quantum algorithms. In particular, for the problem of 3-coloring a circle, prior to our work, no nontrivial limitations on the power of quantum algorithms were known. We managed to show that there is a certain correlation among the colors of non-adjacent vertices that holds for every 3-coloring. As a result, we proved that one round of one way quantum communication is not sufficient to solve the problem.
In cryptography, random permutations, random functions, and various computational problems on them play important roles. However, unlike for random functions, for random permutations we currently do not know many techniques to prove quantum hardness results. We studied the problem of inverting a permutation, and showed how the recently-introduced compressed oracle framework can be used to prove optimal query lower bounds for the problem.
We also studied the computational power of shallow-depth quantum circuits for parity that permit controlled single-qubit gates of unbounded number of control bits. While these unbounded gates might make the model much more powerful, we obtained some preliminary results suggesting that that is not the case. In particular, we classified topologies of all depth-2 circuits in few classes, and for most of them we already showed that they cannot compute the parity of more than 4 input bits, which is already achievable by one and two qubit gates.
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