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Research Highlights

Getting more for less from a Majorana quantum computer

Campbell K. McLauchlan and Benjamin Béri

The proposed hardware, composed of a network of superconducting islands.

The proposed hardware is composed of a network of superconducting islands, shown in blue, in proximity to spin-orbit nanowires (yellow). Majorana zero modes (dashed circles) appear at junctions where three wires meet. Switching on/off the couplings (red) between islands allows one to perform arbitrary multi-Majorana measurements.

New theoretical research expands the capacity of so-called Majorana-based quantum computers, while eliminating key challenges for their operation.

A major obstacle in developing a large-scale quantum computer is decoherence, a mechanism compromising the state of the qubits used by the computer. Majorana zero modes (MZMs), exotic objects emerging in certain superconducting devices, are promising candidates for quantum computing because they offer a hardware-level protection of quantum information from decoherence. Despite this promise, building programmable devices with large numbers of MZMs remains a significant challenge.

In this work, the researchers describe how to achieve a “virtual” increase in the number of MZMs at one’s disposal, by supplementing the quantum parts of a computation with classical processing. The approach not only proposes to compress the size of quantum devices, but also to operate without logic gates: except for an initialisation step and measurements, it eliminates the need to perform quantum operations altogether. In particular, it completely avoids having to exchange (or "braid") MZMs, a highly challenging operation central to existing methods. However, to achieve these resource savings, quantum measurements must be performed on several MZMs simultaneously, another potential challenge. To address this, the authors introduce a hardware design that is well-suited to this type of measurement. With their hardware, one can perform all required measurements without the extra ingredients required by other designs, such as supplementary braids or ancillary MZMs.

This work points towards new avenues for research into resource-efficient methods for MZM quantum computing, enhancing the long-term feasibility of this technology.

Fermion-Parity-Based Computation and Its Majorana-Zero-Mode Implementation, Campbell K. McLauchlan and Benjamin Béri, Phys. Rev. Lett. 128, 180504 (2022).

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