Resource Optimal Realization of Fault-Tolerant Quantum Circuit
Abhoy Kole, Indranil Sengupta
Encoding of quantum information and carrying out computation on encoded state is an essential requirement for improving the reliability of a quantum computer. Resource limitation in today's noisy intermediate scale quantum (NISQ) processors further restricts carrying out fault-tolerant quantum gate operations on such systems. Recent experiments conducted on physical qubits of superconducting transmon type and trapped atomic ions using the fault-tolerant scheme based on [[4, 2, 2]] code have shown a systematic improvement in the fidelity of all logical quantum gate operations except the logical controlled-NOT (CNOT) operation that requires 3 physical SWAP operations for fault-tolerant realization. In this present work we propose an optimal realization of logical CNOT operations on a single or two separate [[4, 2, 2]] code-words using 4 physical CNOT operations and an additional qubit. We further introduce logical two-qubit positive and negative controlled-phase operations with varying rotation angle, and also propose the fault-tolerant realization of logical 2-controlled-phase (C2Z) and 2-controlled-NOT (C2NOT) operations that are required for universal computation using [[4, 2, 2]] encoding. The implementation requires less number of encoded operations and one additional qubit. Through experiments conducted on the 15-qubit IBM Quantum Experience processor and QASM simulator the fidelity and validity of all these proposed gate operations have been verified.
IEEE International Test Conference India (ITC India)•Jul 1, 2020•2 citations