Joint Seminar on Quantum Information and Technologies

A linear optics-based scheme to implement various quantum information processing tasks is of paramount importance due to ease of implementation and low noise. Many information-theoretic tasks depend on the successful discrimination of Bell states. A no-go theorem has been proved in literature which tells that it is not possible to perfectly discriminate among the four Bell states by restricting measurement apparatus to linear optical elements. The success probability is only 50%. Through using extra resources such as hyper entanglement, ancillary entanglement, and even a minimum amount of non-linearity complete Bell-state discrimination can be achieved. The success probability for Bell-like state discrimination is only 25%. We find that this can be boosted up to 50% using hyperentanglement in polarization, momentum, or OAM degrees of freedom of the photons which is in contrast to the Bell-state discrimination scenario where 100% can be achieved. Furthermore, we find that by using correlation in time of the photons all four Bell states can be distinguished with 100% success probability while for the Bell-like state discrimination, it strictly lies between 25% and 50% depending on the state parameter with only three Bell-like states being distinguishable. We also observe a similar contrast when we use ancillary entangled photons. While the success probability for all four Bell-state discrimination increases as $1 − 1/2^N$ where $N$ is the number of ancillary photons for Bell-like states it depends again on the state parametersand can be less than 25% in some cases. Also adding further ancillary photons decreases the success probability. We then show that using non-linear gadgets namely SFG 100% success probability can be achieved even forBell-like state discrimination.[Based on the joint work arXiv:2402.00832 (quant-ph) with Jatin Ghai]