  In the age of post-Moore era, the next-generation computing model would be a
hybrid architecture consisting of different physical components such as
photonic chips. In 2008, it has been proposed that the solving of NAND-tree
problem can be sped up by quantum walk. Such scheme is groundbreaking due to
the universality of NAND gate. However, experimental demonstration has never
been achieved so far, mostly due to the challenge in preparing the propagating
initial state. Here we propose an alternative solution by including a structure
called "quantum slide", where a propagating Gaussian wave-packet can be
generated deterministically along a properly-engineered chain. In this way, the
optical computation can be achieved with ordinary laser light instead of single
photon, and the output can be obtained by single-shot measurements instead of
repeated quantum measurements. In our experimental demonstration, the optical
NAND-tree is capable of solving computational problems with a total of four
input bits, based on the femtosecond laser 3D direct-writing technique on a
photonic chip. These results remove one main roadblock to photonic NAND-tree
computation, and the construction of quantum slide may find other interesting
applications in quantum information and quantum optics.
