A random access memory, or RAM, is a device that, when interrogated, returns
the content of a memory location in a memory array. A quantum RAM, or qRAM,
allows one to access superpositions of memory sites, which may contain either
quantum or classical information. RAMs and qRAMs with n-bit addresses can
access 2^n memory sites. Any design for a RAM or qRAM then requires O(2^n)
two-bit logic gates. At first sight this requirement might seem to make large
scale quantum versions of such devices impractical, due to the difficulty of
constructing and operating coherent devices with large numbers of quantum logic
gates. Here we analyze two different RAM architectures (the conventional fanout
and the "bucket brigade") and propose some proof-of-principle implementations
which show that in principle only O(n) two-qubit physical interactions need
take place during each qRAM call. That is, although a qRAM needs O(2^n) quantum
logic gates, only O(n) need to be activated during a memory call. The resulting
decrease in resources could give rise to the construction of large qRAMs that
could operate without the need for extensive quantum error correction.

分析传统分叉结构和 “桶式队列” 两种随机存取器（RAM）架构，并提出了一些原型实现，显示出在每个 qRAM 调用期间只需要进行 O（n）个二量子比特物理互动，从而减少所需资源，可以构建大型 qRAMs，无需广泛的量子纠错。