  This is the second paper in a series of two. Using a multi-particle
continuous-time quantum walk with two internal states, which has been
formulated in the first paper (arXiv:2112.08119), we physically implement a
quantum random access memory (qRAM). Data with address information are
dual-rail encoded into quantum walkers. The walkers pass through perfect binary
trees to access the designated memory cells and copy the data stored in the
cells. A roundabout gate allocated at each node serves as a router to move the
walker from the parent node to one of two child nodes, depending on the
internal state of the walker. In this process, the address information is
sequentially encoded into the internal states so that the walkers are
adequately delivered to the target cells. The present qRAM, which processes
$2^n$ $m$-qubit data, is implemented in a quantum circuit of depth
$O(n\log(n+m))$ and requires $O(n+m)$ qubit resources. This is more efficient
than the conventional bucket-brigade qRAM that requires $O(n^2+nm)$ steps and
$O(2^{n}+m)$ qubit resources for processing. Moreover, since the walkers are
not entangled with any device on the binary trees, the cost of maintaining
coherence can be reduced. Notably, by simply passing quantum walkers through
binary trees, data can be automatically extracted in a quantum superposition
state. In other words, any time-dependent control is not required.
