The advancements in quantum error-correction and fault-tolerant QIP have shown that in principle scalable quantum computation is achievable. This is a crucial result because it suggests that experimental efforts in QIP will eventually lead to more than a few small scale applications of quantum information to communication and problems with few qubits. However, the general techniques for achieving scalability that are known are difficult to realize. Existing technologies are far from achieving sufficient accuracy even for just two qubits--at least in terms of the demands of the usual accuracy threshold theorems. There is hope that more optimistic thresholds can be shown to apply if one considers the specific constraints of a physical device, better understands the dominant sources of errors, and exploits tailor-made ways of embedding quantum information into subsystems. Current work in this area is focused on finding such methods of quantum error control. These methods include approaches to error control not covered in this introduction--for example, techniques for actively turning off the error-inducing environmental interactions [35,36] and modifications to controlling quantum systems that eliminate systematic and calibration errors [37,38]. Further work is also needed to improve the thresholds for the more pessimistic error models and for developing more-efficient scalability schemes.
Acknowledgements: We thank Nikki Cooper and Ileana Buican for their extensive encouragement and editorial help.
Addresses:
| E. Knill: | Los Alamos National Laboratory | knill@lanl.gov |
| R. Laflamme: | University of Waterloo and Perimeter Institute | laflamme@iqc.ca |
| A. Ashikhmin: | Bell Labs, Lucent | aea@research.bell-labs.com |
| H. Barnum: | Los Alamos National Laboratory | barnum@lanl.gov |
| L. Viola: | '' | lviola@lanl.gov |
| W. H. Zurek: | '' | whz@lanl.gov |