A transmonbased quantum halfadder scheme
Abstract
A fourlevel qubit system is applied to realize quantum halfadder operation. The halfadder circuit is obtained in terms of a quantum CPHASE gate realized by the qubits comprised of four energy levels [C. P. Yang, Prog. Theor. Phys. 128, 587 (2012)], and such a CPHASE gate is demonstrated using the transmon. Commonly, higher energy levels are very sensitive and are easily perturbed by the noise sources. Compared to other qubit systems, the higher energy levels of the transmon are less prone to noise such as charge noise, flux noise and other noises. Further, the order of the dephasing time of the higher energy levels (third and fourth energy levels) is nearly the same as that of the lower energy levels of the transmon when the ratio between the Josephson energy and the charging energy ≫ 1. A system of three transmons coupled to a single high qualityfactor superconducting coplanar resonator is demonstrated to obtain two and threequbit CPHASE gates which are in turn used to obtain the quantum halfadder operation. The main advantage of this quantum halfadder scheme is the reduction in the number of required elementary gates, leading to a significant increase in operational speed and robustness compared to the other existing halfadder schemes. The operational time of a complete halfadder operation is ∼ 37 ns. The methods presented in this article can also be implemented for more complicated quantum circuits.
 Publication:

Progress of Theoretical and Experimental Physics
 Pub Date:
 September 2015
 DOI:
 10.1093/ptep/ptv122
 Bibcode:
 2015PTEP.2015i3A02C
 Keywords:

 A61