NMR quantum computing

Abstract:

Composite pulses have found widespread use in both conventional Nuclear Magnetic Resonance experiments and in experimental quantum information processing to reduce the effects of systematic errors. Here we describe several families of time symmetric and antisymmetric fully compensating composite pulses, inspired by the previous Fn, Gn and BB1 families family developed by Wimperis. We describe families of composite 180° pulses (not gates) which exhibit unprecedented tolerance of pulse strength errors without unreasonable sensitivity to off-resonance errors, and related families with more exotic tailored responses. Next we address the problem of extending these methods to other rotation angles, and discuss numerical results for 90° pulses. Finally we demonstrate the performance of some 90° and 180° pulses in NMR experiments.

Abstract:

Generic models of two and three coupled two-level system (TLS) entangled through their interaction with a single mode field sustained in an ideal cavity, including other interactions among TLS, exhibit violation of Bell's and Mermin's inequality periodically in the interaction time of theTLS with the field mode. The effect of the initial states of TLS on the violation of these inequalities are discussed. The entanglement measure in terms of concurrence for these systems is also calculated which matches very well with the violation of Bell's inequality results. These systems can be employed for quantum logic gate implementations useful in quantum computing. © 2012 Old City Publishing, Inc.

Abstract:

We briefly describe the use of gradient ascent pulse engineering (GRAPE) pulses to implement quantum logic gates in nuclear magnetic resonance quantum computers, and discuss a range of simple extensions to the core technique. We then consider a range of difficulties that can arise in practical implementations of GRAPE sequences, reflecting non-idealities in the experimental systems used.