Experiments on quantum entanglement (where several particles behave as a single unit even though they are separated) that won the 2022 Nobel Prize in Physics were a major success for Indian scientists who found an easier way to quantify the amount of entanglement in higher-dimensional systems. The study could help potentially allow a better assessment of the effectiveness of the entangled state for technological applications such as quantum teleportation (a technique for transferring quantum information from a sender at one location to a receiver at a distance), where the success and accuracy of the process depend. on the amount of entanglement just like other quantum communication protocols.
The entangled state is a key state of quantum mechanics and can be used as a resource for quantum communication, quantum computing and information processing tasks that are impossible for classical systems. Higher dimensional systems (dimension greater than two) have been shown to have advantages in both quantum computing and quantum communication. Thus, the experimental realization of higher dimensional entangled states together with the study of entanglement quantification is of fundamental importance.
To date, all relevant investigations aimed at quantification of entanglement have mainly focused on establishing thresholds (maximum/minimum) for measures of entanglement. An existing quantum state characterization method is quantum state tomography (QST), which can then be used to quantify entanglement. As the dimension of the system increases, it requires the determination of an increasing number of parameters.
A method for empirically estimating entanglement for any arbitrary dimensional entangled state was not available. Scientists from the Raman Research Institute (RRI), an autonomous institute of the Department of Science and Technology, in collaboration with scientists from the Institute for Quantum Computing in Canada, have formulated analytical relationships between statistical correlation measures and known entanglement measures for any arbitrary dimensions. Using just two sets of measurements, they experimentally quantified the amount of entanglement in a pair of three-dimensional photonic qutrites at the Quantum Information and Computing Laboratory at RRI, led by Prof. Urbasi Sinha.
Their research, published in the journal Quantum Science and Technology, provides a more experimentally friendly and less cumbersome alternative to QST. It examines the percentage deviation of the entanglement of a given state from the maximally (100% entangled) entangled state quantified by two different entanglement measures. It experimentally demonstrates for the first time this nonequivalence between different degrees of entanglement in a higher dimensional quantum state. The results may initiate a series of studies that may aim to illuminate not only a deeper understanding of how entanglement should be quantified, but also how to better assess the effectiveness of the entangled state for a given technological application.
The central technological importance of the research lies in the context of quantum interconnected information processing, quantum computing and quantum communication protocols, which are the core of quantum technologies of the 21st century. For applications in quantum teleportation and remote state preparation, the fidelity of the process depends on the degree of entanglement given by the respective degree of entanglement. Thus, given any experimentally prepared entangled state, an a priori assessment of how much entangled the state is is critically useful. It is this requirement that this research deals with.
