**Spring Semester
2002**

**Instructor: Dr.
Lomonaco**

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** ****Speaker:**** ****Carl Williams --
NIST**

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** ****Speakers:**** ****Gavin Brennen
& David Song – NIST**

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** ****Speaker:**** ****Bryan Jacobs – JHU/APL**

** ****Title:**** An Optical Approach to Quantum Information
Processing**

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**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.

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** ****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.**

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** ****Speaker:**** ****Sam Osofsky – Metron, Inc.**

** ****Title:**** Fault-tolerant quantum computation**

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**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.**

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