Searching for a pixel's position in a grayscale quantum image with Grover's algorithm

Abstract

This work proposes a circuit implementation of the encoding circuit for an N × N grayscale-based Flexible Representation of Quantum Images (FRQI). The implementation is tested on the Qiskit simulator before being executed on real IBM Quantum hardware. The encoded FRQI, with a searched pixel encoded by a single qubit, is considered an unsorted database with a single table, where the key of the table represents the pixel's position (x, y). The other columns represent the grayscale level at this position and the searched grayscale level, which are encoded by rotation angles and implemented using several multi-controlled rotation gates along the y-axis. Subsequently, Grover 's algorithm is used to retrieve the position from the FRQI after performing a comparison with the given grayscale level of an individual pixel. The physical constraints associated with the IBM quantum device used are discussed, and the limitations of Grover 's algorithm for searching the pixel are addressed.