Spring Semester 2002
Instructor: Dr. Lomonaco
Speaker: Carl Williams -- NIST
Speakers: Gavin Brennen & David Song – NIST
Speaker: Bryan Jacobs – JHU/APL
Title: An Optical Approach to Quantum Information Processing
Abstract: Knill, Laflamme, and Milburn recently showed that non- deterministic quantum logic operations involving photonic qubits can be performed using only linear optical elements, additional ancilla photons, and post-selection based on the output of single-photon detectors [Nature 409, 46 (2001)]. These operations give the desired result with certainty when a specific output from the detectors is obtained, but that will only occur for some fraction of the events.
I will talk about recent experimental demonstrations of two basic logic devices of this kind, a quantum parity check and a destructive controlled-NOT gate. These two devices can be combined with a pair of entangled photons to implement a conventional controlled-NOT gate that succeeds with a probability of 1/4. The use of fast "feed-forward" and controlled single-qubit operations to increase the success probability of the gates will also be discussed.
Speaker: Dennis Lucareli – JHU/APL
Title: Holonomic Quantum Computation with
Squeezed Coherent States
Abstract: When a quantum system undergoes adiabatic evolution subject to a periodic Hamiltonian it acquires a phase after one complete cycle. Berry's surprising discovery was that in addition to the well known dynamical phase associated to the evolution, there is a phase of purely geometric origin. Recently, non-Abelian geometric phases have been proposed as a way of constructing logic gates in a quantum computer. In this talk, I will introduce Holonomic Quantum Computation from the perspective of geometric control theory. Universality, entanglement, and decoherence will be discussed for a model in which adiabatic squeezing and displacing devices are employed to control the quantum information.
Speaker: Sam Osofsky – Metron, Inc.
Title: Fault-tolerant quantum computation
Abstract: Quantum algorithms are predicted to perform certain calculations much faster than classical computers, but in their simplest form the predictions assume that states can be prepared, maintained, manipulated with unitary operations, and have measurements made on them, all without error. However, it is likely that each of these steps will be beset by noise in at least the first generation of quantum computers. Once realistic noise processes are included in the performance predictions for quantum algorithms, will they will still beat classical algorithms? The answer appears to be yes: it has been shown that quantum computations can be made "fault-tolerant" -- in effect, able to successfully perform a large calculation with a reasonable probability of success -- given reasonable assumptions about the noise processes, as long as the probability of error for quantum gate is below a certain threshold. Furthermore, fault tolerance can be achieved without sacrificing the ability of quantum computers to outperform classical machines. This class will survey some of the key concepts in fault-tolerant quantum computation.