No, the physical shares held by a single holder cannot be dematerialised into a joint demat account. Dematerialisation requires the names on the share certificate and of the demat account to be the same. This is to avoid any legal discrepancies by maintaining consistency of the ownership details.

If you currently hold a joint demat account and wish to dematerialise physical shares registered under a single holder's name, you will need to open a new individual demat account in the same name as on the share certificates. Through this individual account, you can dematerialise the shares.