Quantum information processing is the encoding of information in two-level quantum systems called qubits and the manipulation of this information through a series of unitary transformations which can be interpreted as logic gates. Building real quantum computers will require the ability to perform accurate unitary transformations on quantum systems in the presence of realistic errors. Such errors can be divided into two broad categories: random errors, arising from decoherence, which can be tackled by methods such as quantum error correction, and systematic errors, arising from imperfections in control fields. If systematic errors vary slowly in time, or if they vary over a spatial ensemble of qubits, it is necessary to design control sequences which are intrinsically tolerant of a range of error values.

One successful approach, adopted from Nuclear Magnetic Resonance (NMR) experiments, is the use of composite pulses. Here a single rotation about some axis in the xy plane is replaced by a sequence of rotations, such that the combined propagator implements the desired rotation in the absence of errors, while in the presence of small errors the errors in individual rotations do not accumulate but instead mostly cancel out. I will describe two methods to construct robust NOT gates, that is, π rotations about the x axis of the Bloch sphere, using only π rotations around axes in the xy plane. One group of solutions permits the correction of pulse strength errors to arbitrary accuracy using an analytic construction, while the second group seeks short and practical composite pulses which are still highly robust to both pulse strength and off-resonance errors in single-spin systems. Finally I will comment briefly on some recent practical developments in the use of gradient ascent pulse engineering to design control pulses in more complex NMR spin systems.

个人简历：
Prof Jonathan Jones is Professor of Physics at the Oxford Centre for Quantum Computation and Fellow and Tutor in Physics at Brasenose College, Oxford.  He is also affiliated to the Oxford Centre for Technology and Global Affairs and the Oxford Martin School.
After ten years doing research on the application of NMR (Nuclear Magnetic Resonance) experiments to tackle fundamental topics in Chemistry and Biochemistry he switched to using NMR to implement Quantum Information Processing devices, and in 1998 he demonstrated the first complete implementation of a quantum algorithm. For this he was awarded the Marlow Medal 2000 by the Royal Society of Chemistry.  His recent research concentrates on techniques for the precise control of quantum systems, which is essential to implement accurate quantum logic gates.
In addition to his principal research in Physics, Prof Jones believes that the construction of large scale quantum computers would have very major implications for society through its impact on computer security.  He has spoken on the effects of quantum computing on current electronic commerce and planned electronic governance to commercial and governance audiences.He is the author or co-author of eighty research papers and two books.