Scientific Progress and Accomplishments -

a. Fault-tolerant quantum computing -

Professor John Preskill’s group has developed new methods for error avoidance that work effectively even when the quantum computer makes occasional mistakes (e.g., due to dissipation to the external environment). In these methods, quantum information is redundantly encoded so that errors that are sufficiently infrequent can be systematically corrected, and the processing of the information follows a strict protocol to prevent the propagation of errors throughout the device. Hence, an arbitrarily long quantum computation can be performed reliably, provided that the average probability of error per logic gate is below a certain critical value.

b. Capacity of a noisy quantum channel -

Professor Seth Lloyd has analyzed the limits to the amount of quantum information that can be transmitted reliably down a noisy, dechorent quantum channel. This work addresses the quantum analog of Shannon’s bound for capacity of a noisy classical channel. Drs. Chris Adami and Nicolas Cerf have also investigated this problem as an application of their quantum information theory of entanglement.

c. Distributed quantum computation and communication -

In collaboration with Professors I. Cirac and P. Zoller, Professor Jeff Kimble and graduate student Hideo Mabuchi have proposed and analyzed a realistic scheme for the distribution of quantum entanglement. Their scheme exploits internal atomic states as quantum nodes with photons serving to transport entanglement along quantum channels among the nodes of a quantum network.

d. Impact of errors on quantum computer architectures -

Professor Alvin Depain and graduate student Kevin Obenland have implemented large-scale simulations of quantum circuits which employ detailed models of physical processes relevant to the operation of actual quantum gates. Beyond an assessment of the fidelity of quantum gates required for extensive quantum calculations, their work allows simpler models to be validated, which can in turn be used to study yet more complex calculations and circuits.

e. Quantum circuits as a many-body problem -

Professor Steve Koonin and his group have applied quantum many-body techniques to the 3-SAT problem in an attempt to obtain efficient simulation algorithms.