Six army regiments each have six officers of six different ranks. Can the 36 officers be arranged in a 6-by-6 square so that no row or column repeats a rank or regiment?
This problem was first posed by the Swiss mathematician Leonhard Euler in 1779 has puzzled mathematicians and scientists for centuries! Thanks to quantum physics, the problem has now got a solution. The work was done by two physicists from IIT Madras, Prof. Arul Lakshminarayana and Suhail Ahmad Rather in collaboration with polish researchers Adam Burchardt, Wojciech Bruzda, Grzegorz Rajchel-Mieldzioć and Karol Życzkowski from Jagiellonian University, and the Polish Academy of Sciences.
The paper on the complete solution can be found here.