Quantum entanglement – once deemed by Albert Einstein as “spooky action at a distance” – continues to intrigue the public and challenge seasoned scientists alike.
However, for contemporary quantum researchers, entanglement is a more routine phenomenon: it’s a fundamental connection between particles that serves as a key attribute of quantum computers.
Despite being in their developmental stages, quantum entanglement facilitates tasks that are beyond the capabilities of classical computers, including more accurate simulations of natural quantum systems such as molecules, drugs, and catalysts.
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In a recent study published in Science, my colleagues and I revealed quantum entanglement demonstrated between two atomic nuclei separated by approximately 20 nanometres.
This distance might seem trivial, but our approach marks a notable advancement that could pave the way for quantum computers utilizing a highly precise and reliable method of storing quantum information.
Balancing Control with Noise
The primary challenge for quantum computer engineers lies in maintaining equilibrium between two conflicting requirements.
On one hand, the delicate components must be insulated from external disturbances and noise. On the other hand, they require operability to execute consequential computations.
This necessity fuels the variety of hardware still vying to become the first functional quantum computer.
Some systems excel in executing rapid operations but are plagued with noise. Others are well-shielded from noise but present operational and scalability challenges.
Facilitating Communication Among Atomic Nuclei
My team has been engaging with a platform that has, until now, been categorized in the latter category. We’ve incorporated phosphorus atoms into silicon chips, utilizing the spins of the core atoms for encoding quantum data.
To create an efficient quantum computer, we need to manage numerous atomic nuclei simultaneously. However, until now, the only viable method for interacting with several atomic nuclei was to situate them in close proximity within a solid medium, where they could be encased by a single electron.
While it is conventional to view an electron as significantly smaller than an atomic nucleus, quantum mechanics reveals that an electron can “spread out” across space, allowing it to interact with multiple atomic nuclei simultaneously.
Nevertheless, the electron’s range of influence is rather limited. Furthermore, increasing the number of nuclei sharing an electron complicates the individual control of each nucleus.
Electronic ‘Telephones’ Enable Remote Nuclei Entanglement
Previously, one could liken the nuclei to individuals confined in soundproof rooms. They could communicate effectively as long as they remained in the same enclosed space, but they were oblivious to outside voices, and only a limited number of people could fit within the room. As such, this communication method could not scale.
In our groundbreaking research, we have essentially provided these “people” with telephones, allowing them to converse with others in different rooms. Each room remains peaceful, yet now we can facilitate communication among a greater number of individuals, even if they are distanced.
By having each electron directly linked to an atomic nucleus, we have enabled the nuclei to communicate through their electron interactions.
Utilizing the electron channel, we generated quantum entanglement among the nuclei via a technique known as the “geometric gate.” This method was previously employed a few years ago to perform high-precision quantum operations with silicon atoms.
Notably, we have demonstrated that this technique can scale up for nuclei that are not merely paired with the same electron, a milestone achievement in the realm of silicon-based quantum technology.
Integrating into Standard Circuits
In our experiment, the phosphorus nuclei were spaced 20 nanometres apart. While this distance may seem small, it actually represents fewer than 40 silicon atoms between the two phosphorus atoms.
This separation is also on par with the scale at which conventional silicon transistors are manufactured. Achieving quantum entanglement at this 20-nanometre scale indicates that we can seamlessly integrate our stable, well-shielded nuclear spin qubits into the existing framework of standard silicon chips, such as those found in our smartphones and computers.
Looking to the future, we anticipate extending the entanglement distance even further, as electrons can be manipulated or shaped into more elongated configurations.
This latest achievement signals that advancements in electron-based quantum devices could transform quantum computing into a reality, utilizing lasting nuclear spins to ensure reliable computational outcomes.
Andrea Morello, Professor, Quantum Nanosystems, UNSW Sydney
This article is republished from The Conversation under a Creative Commons license. Read the original article.
