A Compact Gray-Code Quantum Read-only Memory for the NISQ Era

Hao Yu Lu1, Yu-Ting Kao2, Yeong-Jar Chang2, Chao-Hung Wang1, Darsen Lu1
1National Cheng Kung University, 2Industrial Technology Research Institute


Abstract

We propose a programmable quantum read-only memory based on Gray code encoding, termed GQROM, designed to efficiently load classical data into quantum circuits. This architecture mitigates critical bottlenecks in near-term quantum computing by reducing initialization overhead and gate-induced errors. By utilizing Gray-code, where consecutive addresses differ by only a single bit, GQROM minimizes the state transition complexity. We demonstrate that this method reduces the required gate count to about one-third of conventional implementations for the 5-bit address (data size equal to 32) case and beyond. Furthermore, the architecture's flexibility in accessing targeted data via initial state modification is also demonstrated. The entire design, including a systematic EDA flow, was implemented and validated on the Qiskit platform, confirming its practical feasibility. These results underscore GQROM's potential as a scalable and hardware-friendly solution for efficient state preparation in quantum circuits.