Microsoft’s Hunt for a Topological Quantum Computer Qubit
Microsoft is developing Majorana-based topological quantum computer qubits which will be higher-quality and lower error rate qubits. A high-quality hybrid system made of InSb nanowires with epitaxial-grown Al shells has revealed ballistic superconductivity and quantized zero-bias conductance peak. This holds great promise for making the long-sought topological quantum qubits.
Theorists have already begun designing solid-state qubits using the hypothesized quasiparticle. Researcher Pendharkar and his adviser, physicist Chris Palmstrøm of UCSB, say that it will likely be decades before anyone makes a topological qubit.
The key advantage of Microsoft's topological qubit is that fewer physical qubits are needed to make one logical qubit. One logical qubit will require 10 to 100 physical qubits with Microsoft's topological qubits. That compares to something like 1,000 to 20,000 physical qubits for other approaches. This would be for error-corrected qubits which would be needed for lengthy calculations that use many qubits. Non-error corrected qubits will top out at about 100 to 1000 qubits.
The building block for a topological qubit is a superconductor-semiconductor island hosting a pair of Majorana zero modes (called Majorana island). The state of the topological qubit is the combination of the even/odd parity of such Majorana islands. Systematic studies of a Majorana island are crucial to understanding the status of the topological qubit.
First, by performing tunneling spectroscopy measurements, researchers use the ballistic superconductivity and quantized zero-bias peak to support the high-quality and potential `Majorana' properties of the island.
Secondly, the even-odd ground state phase diagram as a function of chemical potential is mapped out and provides a guideline for the topological qubit.
Thirdly, how the superconducting gap and effective g-factor influence the phase diagram is also studied. Such a systematic mapping of the Majorana island is also suitable for double islands, leading towards topological qubits based on multiple islands.
Microsoft has been working on a qubit technology called a topological qubit that it expects will deliver benefits from quantum computing technology that today are mostly just a promise. After spending five years figuring out the complicated hardware of topological qubits, the company is almost ready to put them to use, said Krysta Svore, general manager of Microsoft's quantum computing software work.
“We've really spent the recent few years developing that technology,” Svore said Thursday after a talk at the IEEE International Conference on Rebooting Computing. “We believe we're very close to having that.”
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