Simulating Large Quantum Circuits on a Small Quantum Computer.

Area of Science:

• Quantum Computing
• Computational Physics
• Quantum Information Science

Background:

• Limited quantum memory hinders near-term quantum device capabilities.
• Simulating larger quantum systems on smaller devices is a key challenge.

Purpose of the Study:

• To introduce a novel cluster simulation scheme for quantum circuits.
• To enable simulation of quantum systems exceeding available qubit counts.

Main Methods:

• Decomposition of quantum circuit tensor networks into clusters.
• Development of a cluster simulation scheme based on parameters K (inter-cluster communication) and d (cluster size).
• Application to simulating clustered quantum systems and variational eigensolvers.

Main Results:

• A cluster simulation scheme for (K,d)-clustered quantum circuits on d-qubit machines in time complexity roughly 2^{O(K)}.
• Successful simulation of clustered quantum systems, including large molecules.
• Experimental demonstration of a quantum variational eigensolver achieving desired performance with half the qubits for BeH2 molecule energy estimation.

Conclusions:

• The proposed cluster simulation scheme effectively addresses quantum memory limitations.
• This approach facilitates the simulation of complex quantum systems and algorithms on resource-constrained quantum devices.
• Experimental validation confirms the practical applicability for molecular simulations.