Hi @venkat_abhignan ,
80 TB is based on the following calculation:
One state vector of N qubits has 2^N probability amplitudes. Complex numbers require two numbers (one for the real part and one for the imaginary part) of 8 bytes each. That means that you need 2^N*16 bytes of RAM to store a state vector of N qubits.
Let’s do the math for N=40.
2^40*16 bytes = 1.76e13 bytes = 17.6 TB
However in reality you can’t use 100% of your RAM just to store one state vector. A good rule of thumb is that you should only use about 25-50% of your RAM for this since your computer will need the additional RAM to do other processes and manipulate this number.
So if we go with 25% this means 4 * 17.6 TB = 70 TB
We have ran these very large simulations (see this paper for reference) by distributing the state vector into many GPUs.
I think the paper might answer more of your questions but please let me know if you have more questions after reading the paper!