What
is the physical nature of information? Recent research has shown that the answer
is profoundly connected to quantum theory. Information is physical and can exist
in superpositions, or become entangled. These are unique quantum features, which
make the study of quantum information much more interesting and challenging
then classical information.

My research
interests are primarily in the related field of quantum information processing.
The ultimate information processor is a quantum computer: a computer that uses
quantum bits ("qubits") and quantum circuitry to perform calculations.
Quantum computers can tackle problems that would stymie their conventional (i.e.,
classical) counterparts. For instance, cracking the most sophisticated encryption
schemes, performing many-body correlated-electrons simulations, or searching
large random lists. Small quantum computers can act as nodes in a perfectly
secure quantum communications network. These applications, and many others,
have led to an explosive multidisciplinary effort to understand what it would
take to build quantum computers.

The toughest
problem is the process of decoherence. This is the result of the interaction
of a quantum system with its environment. The environment "measures"
the system and collapses superpositions. A quantum computer must be protected
from decoherence, since this process introduces computational errors and causes
a slowdown to classical speeds. One project I am very interested in is the design
of "quantum error correction" methods that circumvent the decoherence
problem.

Another
fundamental problem is to identify the optimal physical system to serve as a
quantum computer. Many proposals have been made, some have even been implemented
experimentally on a very small scale (e.g., NMR), but so far it is unclear if
these implementations can be scaled up to construct a truly useful quantum computer.
A very promising architecture are quantum dots: artificially patterned semiconductors
that confine electrons in three spatial dimensions on a nanometer scale. Each
confined electron can serve as a qubit, with the quantum information encoded
into the electron spin, position, or energy level. A second project of great
interest to me is the study of quantum dots as a medium to implement quantum
computers. Quantum dots may not be optimal either, however, and I am considering
other media as well.

A third
major research interest of mine is the extension of the theory of quantum control
to deal with open quantum systems. Contrary to the popular textbook view, quantum
systems are not closed, since any real system interacts with its environment
in some uncontrollable way (and thus decoheres). Quantum control aims to steer
a quantum system along a desired trajectory, e.g., in order to optimize the
yield of a chemical reaction, or to process information. While quantum control
theory is well developed for closed systems (governed by the Schrodinger equation),
very little is known about quantum control in the presence of decoherence and
noise. This is a fascinating open field, with many potential applications.

**Selected publications**

1. | A. Hamma and D.A. Lidar, "Adiabatic Preparation of Topological Order", Phys. Rev. Lett. 100, 030502 (2008). |

2. | R.L. Kosut, A. Shabani, and D.A. Lidar, "Robust Quantum Error Correction via Convex Optimization", Phys. Rev. Lett. 100, 020502 (2008). |

3. | A. Mizel, D.A. Lidar, and M. Mitchell, "Simple Proof of Equivalence Between Adiabatic Quantum Computation and the Circuit Model", Phys. Rev. Lett. 99, 070502 (2007). |

4. | M. Friesen, A. Biswas, X. Hu, and D.A. Lidar, "Efficient multiqubit entanglement via a spin-bus", Phys. Rev. Lett. 98, 230503 (2007). |

5. | M. Mohseni and D.A. Lidar, "Direct Characterization of Quantum Dynamics", Phys. Rev. Lett. 97, 170501 (2006). |

6. | M.S. Sarandy and D.A. Lidar, "Adiabatic Quantum Computation in Open Systems", Phys. Rev. Lett. 95, 250503-4 (2005). |

7. | K. Khodjasteh and D.A. Lidar, "Fault-Tolerant Quantum Dynamical Decoupling", Phys. Rev. Lett. 95, 180501-4 (2005). |

8. | L.-A. Wu, P. Zanardi, and D.A. Lidar, "Holonomic Quantum Computation in Decoherence-Free Subspaces", Phys. Rev. Lett. 95, 130501-4 (2005). |

9. | M. Mohseni and D.A. Lidar, "Fault-Tolerant Quantum Computation via Exchange Interactions", Phys. Rev. Lett. 94, 040507-4 (2005). |

10. | L.-A. Wu, M.S. Sarandy, and D.A. Lidar, "Quantum Phase Transitions and Bipartite Entanglement", Phys. Rev. Lett. 93, 250404-4 (2004). |