In 2016, Purdue University and Microsoft have signed a five-year agreement to develop a useable quantum computer. Purdue is one of four international universities in the collaboration. Michael Manfra, Purdue University’s Bill and Dee O’Brien Chair Professor of Physics and Astronomy, professor of materials engineering and professor of electrical and computer engineering, will lead the effort at Purdue to build a robust and scalable quantum computer by producing what scientists call a “topological qubit.”
The team assembled by Microsoft will work on a type of quantum computer that is expected to be especially robust against interference from its surroundings, a situation known in quantum computing as “decoherence.” The “scalable topological quantum computer” is theoretically more stable and less error-prone.
“One of the challenges in quantum computing is that the qubits interact with their environment and lose their quantum information before computations can be completed,” Manfra says. “Topological quantum computing utilizes qubits that store information “non-locally” and the outside noise sources have less effect on the qubit, so we expect it to be more robust.”
The theory of quantum computation can be constructed from the abstract study of anyonic systems. In mathematical terms, these are unitary topological modular functors. They underlie the Jones polynomial and arise in Witten-Chern-Simons theory. The braiding and fusion of anyonic excitations in quantum Hall electron liquids and 2D-magnets are modeled by modular functors, opening a new possibility for the realization of quantum computers. The chief advantage of anyonic computation would be physical error correction: An error rate scaling like e−αℓ, where ℓ is a length scale, and α is some positive constant. In contrast, the “presumptive” qubit-model of quantum computation, which repairs errors combinatorically, requires a fantastically low initial error rate (about 10^−4) before computation can be stabilized.
Manfra says that the most exciting challenge associated with building a topological quantum computer is that the Microsoft team must simultaneously solve problems of material science, condensed matter physics, electrical engineering and computer architecture.
“This is why Microsoft has assembled such a diverse set of talented people to tackle this large-scale problem,” Manfra says. “No one person or group can be expert in all aspects.”
Purdue and Microsoft entered into an agreement in April 2016 that extends their collaboration on quantum computing research, effectively establishing “Station Q Purdue,” one of the “Station Q” experimental research sites that work closely with two “Station Q” theory sites.
Purdue’s role in the project will be to grow and study ultra-pure semiconductors and hybrid systems of semiconductors and superconductors that may form the physical platform upon which a quantum computer is built. Manfra’s group has expertise in a technique called molecular beam epitaxy, and this technique will be used to build low dimensional electron systems that form the basis for quantum bits, or qubits.
The work at Purdue will be done in the Birck Nanotechnology Center in the university’s Discovery Park, and well as in the Department of Physics and Astronomy. The Birck facility houses the multi-chamber molecular beam epitaxy system, in which three fabrication chambers are connected under ultra-high vacuum. It also contains clean-room fabrication, and necessary materials characterization tools.