Majorana Qubit Decoherence Limited by Semiconductor Noise, Study Reveals.

The pursuit of stable quantum computation necessitates exploration of diverse qubit modalities, with Majorana zero modes (MZMs) emerging as a promising avenue due to their inherent topological protection against environmental disturbances. However, realising practical quantum devices utilising MZMs requires overcoming challenges related to qubit coherence, the duration for which quantum information remains stable. New research identifies a significant source of decoherence, the loss of quantum information, stemming from the pervasive presence of 1/f noise – a type of electronic noise exhibiting a frequency-dependent power spectral density – within the semiconductor materials hosting these qubits. This noise induces quasiparticle excitations, disrupting the delicate quantum states and limiting coherence times. A. Alase from the University of Sydney, alongside M. C. Goffage, M. C. Cassidy, and S. N. Coppersmith, all from the University of New South Wales, detail these findings in their article, “Decoherence of Majorana qubits by 1/f noise”, demonstrating that this mechanism poses a fundamental limitation on the performance of MZM qubits, potentially restricting coherence to less than a microsecond even in ideal nanowire structures.

Current research intensely focuses on utilising Majorana Zero Modes (MZMs) within superconductor-semiconductor nanowires as a promising platform for scalable quantum computation, benefiting from predicted low error rates stemming from the topological protection inherent in MZMs. Recent investigations reveal a significant limitation, however, as ubiquitous 1/f noise within semiconductor materials induces a previously unrecognised decoherence mechanism that challenges assumptions of exponentially suppressed decoherence based on nanowire length or temperature. 1/f noise, also known as flicker noise, is a phenomenon where the power spectral density of a signal is inversely proportional to frequency, meaning higher frequency fluctuations are less common, but present across a broad spectrum. This finding represents a substantial obstacle, as predicted decoherence times fall below those required for gate operations and are insufficient when compared to leading alternative solid-state qubit architectures.

Specifically, high-frequency components of 1/f noise generate quasiparticle excitations within the bulk of the topological superconductor, directly contributing to qubit errors and presenting a fundamental scaling challenge. Quasiparticles are excitations in a many-body system that behave like particles, even though they are not fundamental particles themselves. Calculations demonstrate that this noise-induced decoherence limits coherence times of MZM qubits to less than a microsecond, even in perfectly uniform nanowires devoid of disorder, highlighting that topological protection does not fully shield MZM qubits from all environmental noise sources. Topological protection refers to the inherent robustness of MZMs to local perturbations, arising from their non-local nature and the specific symmetries of the system.

Further investigation into the precise origins and characteristics of 1/f noise within these semiconductor-superconductor heterostructures is warranted, as understanding this mechanism is essential to realising the full potential of MZM-based quantum computation. Heterostructures are materials composed of multiple layers of different materials, each with distinct properties. Future work should explore the interplay between this noise-induced decoherence and other known decoherence mechanisms, such as those arising from material imperfections or charge fluctuations, to provide a more realistic assessment of achievable coherence times. A comprehensive understanding of these combined effects is crucial for developing effective strategies to mitigate decoherence and improve the performance of MZM-based quantum computers.