Phys. Rev. Lett.

NMR Implementation of a Molecular Hydrogen Quantum Simulation with Adiabatic State Preparation

from Recent Articles in Phys. Rev. Lett. by Jiangfeng Du, Nanyang Xu, Xinhua Peng, Pengfei Wang, Sanfeng Wu, and Dawei Lu

It is difficult to simulate quantum systems on classical computers, while quantum computers have been proved to be able to efficiently perform such kinds of simulations. We report an NMR implementation simulating the hydrogen molecule (H₂) in a minimal basis to obtain its ground-state energy. Using an iterative NMR interferometer to measure the phase shift, we achieve a 45-bit estimation of the energy value. The efficiency of the adiabatic state preparation is also experimentally tested with various configurations of the same molecule.

Contrasting Spin Dynamics between Underdoped and Overdoped Ba(Fe_{1-x} Co_{x} )_{2} As_{2}

from Recent Articles in Phys. Rev. Lett. by F. L. Ning, K. Ahilan, T. Imai, A. S. Sefat, M. A. McGuire, B. C. Sales, D. Mandrus, P. Cheng, B. Shen, and H.-H Wen

Author(s): F. L. Ning, K. Ahilan, T. Imai, A. S. Sefat, M. A. McGuire, B. C. Sales, D. Mandrus, P. Cheng, B. Shen, and H.-H Wen

We report the first NMR investigation of spin dynamics in the overdoped nonsuperconducting regime of Ba(Fe_1-xCo_x)₂As₂ up to x=0.26. We demonstrate that the absence of interband transitions with large momentum transfer Q_AF∼(π/a,0) between the hole and electron Fermi surfaces results in complete suppression of antiferromagnetic spin fluctuations for x≳0.15. Our experimental results provide direct evidence for a correlation between T_c and the strength of Q_AF antiferromagnetic spin fluctuations.