Newswise — In March 2022, Microsoft released research findings on the achievement of a distinct particle variety that could potentially produce highly durable quantum bits. Presently, scientists at the University of Basel are challenging these findings regarding the alleged Majorana particles, casting uncertainty by demonstrating alternative explanations through calculations.
In 1938, a prodigy mysteriously vanished without a trace: subsequent to purchasing a ferry pass from Palermo to Naples, the Italian physicist Ettore Majorana, in his youth, seemingly evaporated from existence. Merely a few months prior, he had posited an exceedingly peculiar particle variety. These particles were believed to be self-antiparticles, devoid of any electric charge.
In recent years, physicists have experienced a renewed fascination with these enigmatic particles, bearing the name of their absent inventor (whose unexplained disappearance still remains a mystery). Remarkably, it has been discovered that these particles could potentially serve as highly resilient quantum bits in the realm of quantum computing.
The most significant hurdle in the development of these computers, which hold the potential for unimaginable computing prowess, lies in decoherence. In simple terms, this refers to the rapid destruction of delicate quantum states used for calculations due to external disturbances from the environment. However, if Majorana particles could be employed as quantum bits, this predicament could be swiftly resolved. These particles possess inherent resistance to decoherence owing to their unique properties, thus providing a built-in immunity against such disruptive influences.
Dampened expectations
In a recently published study in the esteemed scientific journal Physical Review Letters, scientists from the University of Basel have tempered the prospects of utilizing Majorana particles for practical computation in the foreseeable future. Led by Prof. Jelena Klinovaja, the research team has demonstrated that the outcomes presented by Microsoft in 2022, claiming the detection of Majorana particles in their laboratories, may not be as reliable as initially believed.
Richard David Hess, a PhD student and the primary author of the study, expressed his perspective by stating, "Microsoft's experimental approach is undoubtedly commendable. However, based on our calculations, it appears that the measurement data can also be attributed to alternative phenomena unrelated to Majorana particles."
The quest for exotic particles resembles an intricate detective investigation, where researchers must navigate with only a handful of clues. To uncover these particles, scientists employ a nanowire crafted from a semiconductor material, astonishingly thinner than a human hair, which is intricately connected to a superconductor. Within this system, a fascinating possibility arises: electrons and holes within the semiconductor might form partnerships, giving rise to quasiparticles that exhibit behaviors akin to those of Majorana particles.
Characteristic anomalies
By employing conductance measurements, the researchers at Microsoft successfully identified an anomaly that is indicative of the presence of Majorana states. Furthermore, they demonstrated that the superconducting characteristics of the combined superconductor-nanowire system exhibit a response to an applied magnetic field, implying the existence of a topological phase. These findings provided compelling evidence in support of the presence of Majorana particles within the system under investigation.
In mathematics, topology can be visualized by considering objects such as a coffee cup with a handle, which possesses a distinct "hole." Interestingly, this object can be conceptually transformed or deformed into a doughnut, which also exhibits a similar "hole." Both the coffee cup and the doughnut are considered topologically equivalent. However, a sphere, lacking a "hole," cannot be transformed into either of these shapes. In the context of Majorana states, topology plays a crucial role in providing them with the highly desirable property of being immune to decoherence, making them resilient and robust for quantum computing applications.
Henry Legg, a postdoctoral researcher within Klinovaja's group, elaborates on their approach, stating, "We have conducted mathematical modeling of the experiments conducted by Microsoft and endeavored to explore whether alternative, 'trivial' explanations, in scientific terminology, could account for the measurements." Interestingly, the researchers from Basel have arrived at the conclusion that both the observed anomaly and the superconducting properties can be replicated by introducing a minor level of disorder caused by impurities present within the nanowire.
Jelena Klinovaja emphasizes the significance of disorder in such experiments, stating, "Our findings unequivocally demonstrate the influential role of disorder in these experiments." To achieve unambiguous detection of Majorana states and effectively harness their potential in quantum computers, it will be necessary to advance towards even purer nanowires. This implies that the coming years will present a multitude of experimental challenges that need to be overcome.
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