Pulse optimization for multi-qubit gates in transmon system

Abstract

In transmon qubits, the leading source of errors for quantum gates is the existence of higher energy levels, besides the |0> and |1> states which form the computational subspace. Several methods have been developed to eliminate these errors systematically by clever use of the available experimental controls. In this bachelor thesis we focus on performing quantum gates on multiple qubits simultaneously, when transition frequencies of different qubits are close to each other. The existing solution is designed to perform a quantum gate on one qubit, while eliminating all the effects on the other one. We develop a procedure to create new analytic pulse shapes which produce low-error gates for single qubits and we generalize this approach to multi-qubit systems to apply multiple quantum gates at the same time. For both single- and two-qubit gates these new pulses reduce errors by several orders of magnitude compared to simple driving pulses. In addition we combine these optimal analytical pulse shapes with multi-parameter pulses. The parameters of this additional pulse are optimized numerically, to produce even lower gate errors.