Noise tolerance of photonic entanglement can be significantly enhanced

Quantum measurements are prone to noise, which can enter the system in many ways. For quantum communication, increasing the system’s dimensionality – the number of available encoding levels – can increase its resistance to noise.

Zhu et al. studied the noise performance of high-dimensional entanglement, and found the effects are more nuanced than expected. Rather than using a theoretical quantifier for noise, they studied how realistic sources of noise, such as those from loss or background, affect photonic entanglement. They showed that these parameters can be condensed into a single, routinely measured single-to-noise parameter, which is sufficient for predicting the upper bound of how well the system can operate.

“If you know the signal-to-noise ratio, it’s an incredibly powerful predictive measure for future experiments, and it gives you an idea of where you need to get to with your system if you want to have any particular performance,” said author Jonathan Leach.

The group found that modest increases to the size of an entangled photonic system can improve its noise tolerance by multiple orders of magnitude. If the size of the entangled state is kept constant, just doubling the operational dimensions of the system would allow entanglement to be measured with detectors that are hundreds of times less efficient or noisier.

“It shows that by increasing the space by a little bit, we can get away with worse detectors and more lossy channels,” said author Mehul Malik. “If you want to do quantum communication over any realistic distance, you need to tolerate loss.”

Scaling up quantum communication systems for widespread use will require enhanced sensitivity. Leach and Malik say their theory can help achieve this.

Source: “Is high-dimensional photonic entanglement robust to noise?,” by F. Zhu, M. Tyler, N. Valencia, M. Malik, and J. Leach, AVS Quantum Science (2021). The article can be accessed at https://doi.org/10.1116/5.0033889 .