Topological qubits are among the more baffling, and if practical, more promising ways to approach scalable quantum computing. At least that’s what Microsoft, Purdue University, and three other universities are hoping after having recently signed a five-year agreement to develop a topological qubit based quantum computer.
Qubits are strange no matter what form they take. The basic idea being that through superposition, a qubit can be in two states at once (0 and 1) and hence a quantum computer’s capacity scales exponentially with the number of qubits versus classical computers which scale linearly with the number of bits. Most quantum computing efforts rely on producing superposition in some material – IBM uses superconducting devices – and there have been many qubit schemes proposed.
Topological qubits are among the more mysterious. They rely on ‘quasi’ particles called non-abelian anyons which have not definitively been proven to exist. Using these topological qubits, information is encoded by “braiding” the paths of these quasi-particles. The benefit, say researchers, is topological qubits resist decoherence much better than other qubit types and should require far less error correction. At least that’s the theory.
Microsoft has been dabbling in topological qubit theory for several years. Last fall Microsoft quantum researcher Alex Boharov was interviewed by Nature (Inside Microsoft’s quest for a topological quantum computer, October 21, 2016) on why pursue such an exotic path.
“Our qubits are not even material things. But then again, the elementary particles that physicists run in their colliders are not really solid material objects. Here we have non-abelian anyons, which are even fuzzier than normal particles. They are quasiparticles. The most studied kinds of anyon emerge from chains of very cold electrons that are confined at the edge of a 2D surface. These anyons act like both an electron and its antimatter counterpart at the same time, and appear as dense peaks of conductance at each end of the chain. You can measure them with high-precision devices, but not see them under any microscope…” said Boharov.
As explained by Boharov, “Noise from the environment and other parts of the computer is inevitable, and that might cause the intensity and location of the quasiparticle to fluctuate. But that’s OK, because we do not encode information into the quasiparticle itself, but in the order in which we swap positions of the anyons. We call that braiding, because if you draw out a sequence of swaps between neighbouring pairs of anyons in space and time, the lines that they trace look braided. The information is encoded in a ‘topological’ property — that is, a collective property of the system that only changes with macroscopic movements, not small fluctuations.”
The upside is tantalizing he said, “So far, we’ve had an amazing ride in terms of creating more-efficient algorithms — reducing the number of qubit interactions, known as gates, that you need to run certain computations that are impossible on classical computers. In the early 2000s, for example, people thought it would take about 24 billion years to calculate on a quantum computer the energy levels of ferredoxin, which plants use in photosynthesis. Now, through a combination of theory, practice, engineering and simulation, the most optimistic estimates suggest that it may take around an hour. We are continuing to work on these problems, and gradually switching towards more applied work, looking towards quantum chemistry, quantum genomics and things that might be done on a small-to-medium-sized quantum computer.”
Now, Microsoft is further ramping up its quantum efforts with a collaboration that includes Purdue as well as a global experimental group established by Microsoft at the Niels Bohr Institute at the University of Copenhagen in Denmark, TU Delft in the Netherlands, and the University of Sydney, Australia. For Purdue, this is an extension of joint work on quantum computing with Microsoft begun roughly one year ago. Michael Freedman of Microsoft’s Station Q in Santa Barbara leads the effort.
“What’s exciting is that we’re doing the science and engineering hand-in-hand, at the same time,” says Purdue researcher Michael Manfra in an article on the project posted on the Purdue web site yesterday.
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, according to the article.
Purdue President Mitch Daniels noted in the article that Purdue was home to the first computer science department in the United States, and said the partnership and Manfra’s work places the university at the forefront of quantum computing. “Someday quantum computing will move from the laboratory to actual daily use, and when it does, it will signal another explosion of computing power like that brought about by the silicon chip,” Daniels said.
Link to Purdue article written by Steve Tally: http://www.purdue.edu/newsroom/releases/2017/Q2/microsoft,-purdue-collaborate-to-advance-quantum-computing-.html
Caption for feature image: Michael Freedman (left), Microsoft Corp. quantum computing researcher, and Suresh Garimella, executive vice president for research and partnerships, and Purdue’s Goodson Distinguished Professor of Mechanical Engineering, sign a new five-year enhanced collaboration between Purdue and Microsoft to build a robust and scalable quantum computer by producing what scientists call a “topological qubit.” (Purdue University photo/Charles Jischke)