Controlling Majoranas for Next-Gen Quantum Computing

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Ettore Majorana, Italian theoretical physicist

Researchers struggle to find ways to increase the potential power of future quantum computer systems. In an intriguing step on that path, a team from the University of Surrey, UK, and Ben-Gurion University, Israel, has found a way to detect and potentially control solid-state Majorana fermions—quasiparticles that could serve as stable units of quantum information and significantly increase computing power for future quantum information systems (Nature Comm., doi: 10.1038/ncomms5772). The researchers’ proposed hybrid device, which combines different subsystems, presents new methods for better understanding the quasiparticle and harnessing the power of its quantum variables.

Majorana fermions differ from other quantum particles, such as bosons and traditional fermions, in that when they move, their quantum state changes in a way that reflects their path history. Bosons and traditional fermions, by contrast, return to their original state. Majorana fermions’ ability to “remember” their path could be used to encode information for quantum computers. Quantum bits (qubits) made with Majorana fermions could also be less fragile than current real-world qubits that lose their ability to carry data when disturbed by environmental variables, like heat. It’s believed that the woven structure of qubit arrays constructed of Majorana modes—braided like fibers of a rope—would make them more robust carriers of information.

But taking advantage of these characteristics requires ways to detect Majorana signatures and manipulate the fermion’s quantum state, a difficult feat. To crack that problem, the British and Israeli team has designed a proposed a hybrid superconducting device that includes a Cooper-Pair-Box containing a topological nanowire, placed near the Josephson junction between two superconductors. The nanowire is where the scientists believe the Majorana particles exist under specific conditions. Using this hybrid device, the team says, detectible experimental signatures of Majorana fermions could be found by looking for specific patterns via microwave spectroscopy. By using special gate bias points in the device, the researchers believe they can also “switch” the photon-qubit coupling off with quantum interference, thereby controlling the quantum behavior of the Majorana.

The team believes that with further research, Majorana qubits could enable topological superconductors which would exponentially outperform existing eight-qubit quantum computers. They hope their method will undergo performance trials within the next year.

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