# Hardware requirement

Hello, we would like to run simulations of algorithms on 40 qbits, what would be the minimum hardware requirements? Thanks and regards, Venkat Abhignan

Hi @venkat_abhignan , welcome to the Forum!

You would need something like 80 TB RAM. That’s a lot. Of course that depends on what exactly you’re simulating, how deep and how interconnected your circuit is, what techniques you’re using (like circuit cutting), etc.

This should give you a rough idea for a random circuit with a reasonable number of layers.

Dear Catalina Albornoz,

Thank you very much for your input. Have there been cases where 40 qbits simulations have been actually performed on 80 TB RAM. Is there some documentation regarding this based on what processors are also required. Or is there a documentation on how these hardware configuration values can be scaled based on number of qubits.

Thanks and regards,
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!