Can someone else operate my demat account on my behalf on the basis of Power of Attorney?

Yes. If you authorize any person to operate your account by executing a power of attorney, that person can operate the account on your behalf. However, you need to submit a Notarised copy of the POA to your DP. Ensure that the POA has the signatures of both, the Donor and the Donee. The POA holder is also subject to KYC norms of the bank. However if the POA is submitted at the time of account opening, it is mandatory that the holder signs the account opening document.