Finding Short Vectors in Structured Lattices with Reduced Quantum Resources

Leading protocols of post-quantum cryptosystems are based on the mathematical problem of finding short vectors in structured lattices. It is assumed that the structure of these lattices does not give an advantage for quantum and classical algorithms attempting to find short vectors. In this work we focus on cyclic and nega-cyclic lattices and give a quantum algorithmic framework of how to exploit the symmetries underlying these lattices. This framework leads to a significant saving in the quantum resources (e.g. qubits count and circuit depth) required for implementing a quantum algorithm attempting to find short vectors. We benchmark the proposed framework with the variational quantum eigensolver, and show that it leads to better results while reducing the qubits count and the circuit depth. The framework is also applicable to classical algorithms aimed at finding short vectors in structured lattices, and in this regard it could be seen as a quantum-inspired approach.