  Continuous-time quantum walk is one of the alternative approaches to quantum
computation, where a universal set of quantum gates can be achieved by
scattering a quantum walker on some specially-designed structures embedded in a
sparse graph [Childs, Phys. Rev. Lett. 2009]. Recent advances in femtosecond
laser-inscribed optical waveguides represent a promising physical platform for
realizing this quantum-walk model of quantum computation. However, the major
challenge is the problem of preparing a plane-wave initial state. Previously,
the idea of quantum slide has been proposed and experimentally realized for
demonstrating the working principle of NAND tree [Wang et al. Phy. Rev. Lett.
2020]. Here we show how quantum slide can be further applied to realize
universal quantum computation, bypassing the plane-wave requirement.
Specifically, we apply an external field to the perfect-state-transfer chain,
which can generate a moving Gaussian wave packet with an arbitrary momentum.
When the phase is properly tuned, the universal gate set in Childs' proposal
can be realized in our scheme. Furthermore, we show that the gate fidelities
increase with the length of the slide, and can reach unity asymptotically.
