Intrinsic Error Mitigation in the Cascaded Variational Quantum Eigensolver*

We present results obtained using the Cascaded Variational Quantum Eigensolver (CVQE) algorithm.  The results indicate the parameter optimization process within CVQE automatically and substantially mitigates the errors introduced during quantum circuit executions.  This is possible because all of the errors are introduced before the optimization process begins in the CVQE algorithm.  In contrast, these errors are introduced at every iteration of the optimization process in other Variational Quantum Eigensolver (VQE) algorithms.  Furthermore, because the entire ansatz in the VQE algorithm is implemented in a quantum circuit, the solution will necessarily be sensitive to quantum errors.  In CVQE, only a portion of the ansatz is implemented in the quantum circuit and the variational parameters are not implemented in this circuit.  Thus, the variational parameters are able to freely evolve to compensate for initial errors during the circuit executions.  Consequently, the CVQE algorithm could be capable of simulating systems within a certain error tolerance that would otherwise be impossible using present-day quantum computers.