Abstract: A quantum computer can solve certain important classes of problems that are otherwise too difficult for a classical computer. A qubit, or quantum bit, can be encoded in the singlet and triplet states of two electron spins. Its states are represented as points on the unit sphere—Bloch sphere. A major obstacle to precise qubit manipulation is decoherence, the error arising from interactions with the environment. While techniques such as dynamical decoupling have been developed in other contexts to compensate such errors, constructing robust quantum gates remains particularly challenging for singlet-triplet spin qubits due to experimental constraints on available control. In this talk, I will discuss theoretically how one may meet this challenge by employing carefully designed composite pulse sequences. I will present composite pulses that serve as dynamically corrected single-qubit gates which are immune to both overhauser noise and charge noise, covering major sources of decoherence. I will further show how a two-qubit gate may be constructed in a noise-resistant manner, and how one can perform arbitrary quantum algorithm on a given spin chain robust against noise. This noise reduction comes with a cost of prolonging the gate time, but the long coherent times for these qubits renders such trade-off practical.

 

About the Speaker: Dr. Xin Wang graduated from Peking University with B.S. in 2005 before he came to the United States. In 2010 he received his Ph.D. from Columbia University in the City of New York. Working under Prof. Andrew J. Millis, his Ph.D. work was focused on theoretical and numerical studies of strongly correlated electron systems such as high-temperature superconductors and quantum dots. He then joined the Condensed Matter Theory Center at University of Maryland, College Park, directed by Prof. Sankar Das Sarma, as a postdoctoral research associate. His current research interests include spin-based quantum computation and strong correlation in cold atom systems.

Date&Time: July 21, 2014 (Monday), 10:30 - 11:30 a.m. 
Location: 606 Conference Room