x**2 should work as well.
a = torch.randn(2, 2)
print a

>> 0.4616  0.2764
>> -0.4579  0.9157
>> [torch.FloatTensor of size 2x2]

print a**2

>> 0.2131  0.0764
>> 0.2096  0.8384
>> [torch.FloatTensor of size 2x2]

Is this what you are looking for?
As @Xinge mentioned, torch.mul(a, a) gives the same result.