NED University of Engineering & Technology: Researchers Model Quantum Gate Fidelity with Light and Spatial Modulators

A thorough simulation of universal quantum gate sets implemented on photonic orbital angular momentum qubits has been demonstrated by Saleha Maqsood and colleagues at NED University of Engineering & Technology. The simulation utilises spatial light modulators to control Laguerre-Gaussian beams, achieving predicted gate fidelities between 0.9914 and 0.9936 through detailed modelling of realistic noise sources. Benchmarked against existing experimental results, the simulation identifies an optimal operating range of 450, 532nm and provides key insights into the practical implementation of high-fidelity quantum operations with this technology.

High-fidelity photonic gate simulations exceed established precision thresholds

Gate fidelities, ranging from 0.9914 to 0.9936, were achieved through detailed simulation, surpassing the previously established 99% threshold for two-qubit gates on a photonic platform. This level of precision was unattainable until now. NED University of Engineering & Technology carefully modelled quantum gate operations using a spatial light modulator, a device shaping light beams to encode information, and a realistic noise measurement totalled 92.4 mrad.

Laguerre-Gaussian beams, light beams shaped like donuts, were utilised in the simulation, which benchmarks competitively against six published experimental studies, indicating performance within a comparable range. The simulation detailed the noise affecting it, identifying three key sources: 8-bit quantisation noise inherent in the spatial light modulator, twisted-nematic electronic and thermal noise within the device, and errors caused by phase-wrap clipping during hologram creation. Universal single-qubit gates, including X, Y, Z, S, T, and H, were successfully modelled. Two-qubit entangling gates like CNOT, CZ, and SWAP were also modelled on a 512×512 grid, achieving Bell state preparation with a fidelity of 0.9914 after two interactions with the SLM. Analysis also revealed optimal performance within a 450-532nm wavelength range, demonstrating a clear understanding of device limitations and potential for optimisation.

Demonstrating 99% fidelity quantum gates with a component-limited noise model

The pursuit of stable, high-fidelity quantum gates using light offers a promising route to scalable quantum computers, yet translating simulations into reliable devices presents ongoing challenges. Achieving gate fidelities exceeding 99% depends on a carefully constructed noise model derived directly from component specifications; however, this model currently operates within a limited 450-532nm wavelength range. Verifying these predicted fidelities with physical experiments, and expanding beyond this spectrum, remains a significant hurdle, as real-world component behaviour often deviates from idealised simulations.

Precise characterisation of these noise sources allows efforts to focus on mitigating the most significant error contributors, which is particularly valuable as quantum systems scale up in complexity and become more susceptible to imperfections. These high fidelities currently apply only to a specific, relatively narrow range of visible light wavelengths, an important consideration for future development. This simulation establishes a key benchmark, and future advancements will likely begin by extending this fidelity beyond visible light and validating predictions with physical devices. Researchers at NED University of Engineering & Technology established a detailed simulation framework to assess the performance of spatial light modulators, devices which shape light to encode quantum information, in photonic quantum computing. Incorporating realistic noise factors directly from component specifications, limitations in the device’s digital resolution, electronic behaviour, and how it handles extreme phase shifts, enabled them to achieve predicted gate fidelities exceeding 99%, representing a key step towards building practical quantum technologies.

Researchers demonstrated predicted quantum gate fidelities of 0.9914, 0.9936 using a spatial light modulator and a detailed noise model. This level of accuracy is important because stable, high-fidelity gates are essential for building scalable quantum computers. The simulation incorporated realistic limitations of the device, including digital resolution and electronic behaviour, and identified an optimal operating range of 450, 532nm. The authors suggest validating these predictions with physical experiments and extending the fidelity beyond visible light wavelengths as next steps.