Linear optical demonstration of quantum speed-up with a single qudit.

Quantum algorithm acts as an important role in quantum computation science, not only for providing a great vision for solving classically unsolvable problems, but also due to the fact that it gives a potential way of understanding quantum physics. We experimentally realize a quantum speed-up algorithm with a single qudit via linear optics and prove that even a single qudit is enough for designing an oracle-based algorithm which can solve a certain problem twice faster than any classical algorithm. The algorithm can be generalized to higher-dimensional systems with the same two-to-one speed-up ratio.