# How to convert code from QISKIT to QuEST using QASM

I have been working on this project which requires a lot of qubits. Originally we have made the whole project in QISKIT as we have been using it for a long time. But the maximum number of qubits that can be simulated in qiskit can not be more than a 100 qubits. Due to which are planning to use QuEST which can simulate a lot more qubits. Now instead of converting the whole code which is taking a lot of time, we were thinking if we could convert the qiskit code for each case into QASM and then use the QASM code to convert to QuEST, this way we will be saving a lot of time. And we found another project which is based on this itself. But as there are not a lot of resources regarding this I am facing a lot of issues with this. I was wondering if you guys had some tips and tricks .

Thanks any help is greatly appreciated!!

• Have you tried using the matrix product state simulation method in Qiskit - qiskit.org/documentation/tutorials/simulators/…? Depending on the amount of entanglement you have in your circuit it should be able to simulate more qubits. Nov 5, 2021 at 14:49
• Yeah using simulator mps we can go upto 100 qubits. This is much more than what qasm simulator offers us. But we need about 250 qubits Nov 6, 2021 at 6:54

Developer of QuEST here. It sounds like QuEST isn't the right tool for your needs. QuEST is a 'full-state' simulator (the 'E' stands for 'exact'), so its memory requirements scale exponentially with the number of simulated qubits. A 250 qubit simulation (at double precision) would require ~10^64 TiB, which you could get by magicking every atom on Earth into a Titan supercomputer.
For a generic quantum circuit, 250 qubits is a very demanding simulation. Are you simulating a specific family of circuits that permit bespoke classical simulation?