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Dr. Frank Gaitan: Working Toward a Functional Quantum Computer

by Editor1 last modified February 28, 2008 - 22:39

For a number of years, Frank Gaitan, an associate professor in Southern Illinois University's (Carbondale, Ill). Department of Physics, followed the field of quantum computing from a distance. But, today, he is actively involved in one of the area’s most intriguing research areas – the hunt for the quantum computer. talks with Dr. Gaitan about his work.

Dr.  Frank Gaitan: Working Toward a Functional Quantum Computer

The Bloch sphere is a representation of a qubit, the fundamental building block of quantum computers.

Dr. Gaitan explains his impetus for becoming involved: “The deciding factor for me was the proof of the accuracy threshold theorem, which showed that quantum computation was possible under appropriate conditions, even in the presence of noise and imperfect quantum gates. … Approximate calculations of this threshold value found that it was small, though non-zero, which indicated that building a quantum computer would be technically challenging, but not impossible.”

The Search for Quantum Computers
Wikipedia posits the following definition of a “quantum computer” A classical computer has a memory made up of bits, where each bit holds either a one or a zero. The device computes by manipulating those bits, (i.e. by transporting these bits from memory to logic gates and back).  In contrast, a “quantum computer” maintains a vector of qubits (or quantum bit) A qubit can hold a one, a zero, or, crucially, a superposition of these. A quantum computer operates by manipulating those qubits, i.e. by transporting these bits from memory to (possibly a suite of) quantum logic gates and back.

It is widely believed that if large-scale quantum computers can be built, they will be able to solve certain problems exponentially faster than any classical computer. Quantum computers are different from other computers such as DNA computers and traditional computers based on transistors, even though all transistors are ultimately based on quantum mechanical effects (for example depletion regions). Some computing architectures such as optical computers may use classical superposition of electromagnetic waves, but without some specifically quantum mechanical resource such as entanglement, they do not share the potential for computational speed-up of quantum computers.

State of Dr. Gaitan's Research
This definition leads researchers such as Dr. Gaitan to look for answers to a yet-unsolved problem in physics. Is it possible to construct a practical computer that performs calculations on qubits.

This motivation is fueling his work to overcome the challenges faced by the construction of a functional quantum computer. He explains, “Our work, as well as that of many others, is aimed at finding ways to implement a universal set of quantum gates that operate with error probabilities that fall below the accuracy threshold. This is one of the principal challenges that must be overcome if a working quantum computer is to someday be built.”

In addition, Dr. Gaitan is researching quantum control theory. “Our work is exploring the use of quantum interference effects to enhance the control of quantum systems. These interference effects arise in a class of non-adiabatic rapid passage sweeps known in nuclear magnetic resonance, but which can also be produced using electric fields. Computer simulations indicate that these sweeps can be used to produce a universal set of high fidelity quantum gates; however, high precision control of the sweep parameters is needed to fully realize the potential of these sweeps. Current work is aimed at increasing the robustness of these gates and exploring the manner in which noise and decoherence impact their performance.”

Another reason why Dr. Gaitan felt compelled to work in this research area was because of its interdisciplinary nature. “Research in this field has already established a highly developed theory of quantum error correcting codes and fault-tolerant quantum computing that extends the classical theories that have been studied and developed by mathematicians, electrical engineers, and computer scientists to include the new possibilities that arise when quantum systems are used in the storage and processing of information,” he said. “In a similar vein, interest in quantum communication and computing has given rise to the developing fields of quantum information theory and quantum control theory whose classical counterparts are well-known research areas in mathematics and electrical and mechanical engineering.”

With a clear grasp of the field and his continuing research in quantum computers, de-coherence, and condensed matter physics, Dr. Gaitan is sure to remain at the forefront in the quest for a working quantum computer—“the next frontier in computer technology.”**

**Frank Gaitan quoted in Rod Sievers, “SIUC on the cutting edge of computer research,” July 16, 2002.

Dr. Frank Gaitan has frequently published on quantum computers, including "Simulation of Quantum Adiabatic Search in the Presence of Noise," Int. J. Quantum Info. 4, 843 (2006).  He is also the author of the forthcoming book Quantum Error Correction and Fault Tolerant Quantum Computing (CRC Press, March 2008).