Quantum Random Access Memory

TLDR

RAM uses n bits to address 2^n memory cells, whereas QRAM uses n qubits to address any superposition of 2^n cells. The authors propose an architecture that reduces memory‑call requirements from N to O(log N) switches. This architecture is implemented with a quantum optical system that employs O(log N) switches. The design yields a more robust QRAM algorithm that requires exponentially fewer entangled gates and reduces addressing power exponentially.

Abstract

A random access memory (RAM) uses n bits to randomly address N=2(n) distinct memory cells. A quantum random access memory (QRAM) uses n qubits to address any quantum superposition of N memory cells. We present an architecture that exponentially reduces the requirements for a memory call: O(logN) switches need be thrown instead of the N used in conventional (classical or quantum) RAM designs. This yields a more robust QRAM algorithm, as it in general requires entanglement among exponentially less gates, and leads to an exponential decrease in the power needed for addressing. A quantum optical implementation is presented.