Gate Optimization of NEQR Quantum Circuits via PPRM Transformation

Quantum image representation (QIR) is a key challenge in quantum image processing (QIP) due to the large number of pixels in images, which increases the need for quantum gates and qubits. However, current quantum systems face limitations in run-time complexity and available qubits. This work aims to compress the quantum circuits of the Novel Enhanced Quantum Representation (NEQR) scheme by transforming their Exclusive-Or Sum-of-Products (ESOP) expressions into Positive Polarity Reed-Muller (PPRM) equivalents without adding ancillary qubits. Two cases of run-time complexity, exponential and linear, are considered for NEQR circuits with m controlling qubits ($m \rightarrow \infty$), depending on the decomposition of multi-controlled NOT gates. Using nonlinear regression, the proposed transformation is estimated to reduce the exponential complexity from $O(2^m)$ to $O(1.5^m)$, with a compression ratio approaching 100%. For linear complexity, the transformation is estimated to halve the run-time, with a compression ratio approaching 52%. Tests on six 256$\times$256 images show average reductions of 105.5 times for exponential cases and 2.4 times for linear cases, with average compression ratios of 99.05% and 58.91%, respectively.