Always On Non-Nearest-Neighbor Coupling in Scalable Quantum Computing
  We investigate the non-nearest-neighbor interaction effect in 1-D spin-1/2 chain model. In many previous schemes this long-range coupling is omitted because of its relative weak strength compared with the nearest-neighbor coupling. We show that the quantum gate deviation induced by the omitted long-range interaction depends on not only its strength but also the scale of the system. This implies that omitting the long-range interaction may challenge the scalability of previous schemes. We further consider how to suppress this unwanted effect. We propose a quantum computation scheme. In this scheme, by using appropriate encoding method, we effectively negate the influence of the next-nearest-neighbor interaction in order to improve the precision of quantum gates. We also discuss the feasibility of this scheme in 1-D Josephson charge qubit array system. This work may offer improvement in scalable quantum computing. 
Yong Hu, Zheng-Wei Zhou and Guang-Can Guo