Nanowires help shape future quantum devices

Nanowires are nearly one-dimensional objects with only one dimension measuring just over a few nanometers. Fabricated nanowires have many applications of nanotechnology, including in quantum devices such as quantum computers.

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What are nanowires?

Nanwires are a class of nanostructures, along with nanoparticles, nanotubes, and thin films. Nanowires are tiny wire forms with a diameter of between 0.1 and 100 nanometers and can be thousands of times longer than their thickness.

Nanowires are made from different types of materials depending on the purpose and industrial use. For example, superconducting nanowires are made of YBCO compounds, silver, gold and platinum metallic nanowires, silicon semiconducting nanowires, and insulating nanowires made of silicon or titanium oxide. It is also possible to produce molecular nanowires by duplicating organic molecular units (eg DNA) or other inorganic molecules.

Due to the recent development of manipulation techniques over the past two decades, it is now possible to generate complete mechanical characterizations of nanowires. Processing equipment used to achieve this includes atomic force microscopy (AFM), scanning electron microscopy (SEM), and focus ion beam SEM (FIB-SEM). The introduction of MEMS technology to electron microscopy has also played a role in the recent characterization of nanowires.

Possible applications for nanowires are relatively widespread. They can be used to build future nanoelectromechanical systems (NEMS) technology, as well as make good candidates for advanced composite additives.

Nanowires in quantum devices

At such small proportions, nanowires behave according to the laws of quantum mechanics, making them suitable for applications in quantum devices.

Quantum devices are any technology that has at least one feature that deals with the phenomena of quantum mechanics. Quantum computers, which use quantum superposition to encode bits of data, are one example of quantum devices.

Quantum computers encode qubits (rather than qubits, “binary units”) with information. These systems manipulate quantum mechanical phenomena such as superposition and quantum entanglement to process more data at once than conventional binary computers can do. The result, in theory, is much faster computing power in much smaller processor chips.

Quantum dots are used as qubits in quantum computers. Since they are quantum particles, phenomena such as quantum entanglement and superposition can be induced or manipulated.

At present, the majority of quantum devices that use nanowires to manipulate features of quantum mechanics are quantum electrical devices.

However, nanowires are also under investigation for their use in optical quantum devices. The nanowires can be used as a ballistic photon waveguide in photon logic arrays (a type of optical computing) that use quantum dots to encode information. Photons are sent through the nanowires, with electrons traveling next to them on the outer shell.

In this example, nanowires that act as a photon waveguide are crossed over each other, making a quantum dot at their junction. Quantum dots are quantum semiconductor particles that have important applications in quantum computing, as they can be encoded as qubits.

Quantum dots formed in this way can be used to make pairs of photons that exhibit quantum entanglement. In this phenomenon, two quantum particles (photons in this case) become entangled, so it appears that physical stimuli affecting a single particle also affect their pair even when they are physically separated.

Currently, quantum computing is limited by the highly unstable nature of quantum states. It is difficult to create a manageable set of qubits and maintain their quantum states reliably under normal conditions, and many practical quantum computers need temperatures close to 0 K to function.

One of the proposed quantum computing methods relies on topology to form qubits, which is theoretically more stable. The majorana state of a particle with an antiparticle can hold quantum information in a similar way to pairs of photons or quantum dots.

Researchers are currently developing a nanowire network that will be able to form controllable Majorana states and create the first working topological computer.

In 2022, scientists grew indium arsenide (InAs) nanowires measuring just 20 nanometers using a molecular beam. This method can be applied to build relatively highly stable topological quantum computers.

Looking Ahead: Technology Maturity

Nanowires and other elements of nanotechnology – not to mention their application in quantum devices – are still relatively immature technologies. This means that nanowires and quantum devices are largely (although by no means) limited to research. For example, no company has yet made a commercially viable quantum computer.

Recently, global technology company Intel sought to protect the intellectual property (IP) of a new quantum computing device that uses nanowires to create quantum dots. The benefit of this approach over others is that it is possible to identify quantum dots in space with great accuracy.

The improved spatial resolution will provide improved control over quantum dot processing and make electrostatic controls more responsive. As a result, Intel engineers must have greater design freedom and flexibility about where to place electrical connections and integrate quantum dots into large-scale quantum computers.

A new patent from the world’s leading processing chip manufacturer is a good indication that nanowires and quantum devices are nearing maturity.

Continue reading: Spintronics, 2D Materials, the Future of Quantum

References and additional reading

Domé, (2022). Ultra-thin nanowires could be a boon for error-resistant quantum computing. [Online] Physicist. Available at: https://physicsworld.com/a/ultrathin-nanowires-could-be-a-boon-for-error-resistant-quantum-computing/

Enrico, A.; et al. (2019). Scalable fabrication of single nanowire devices using slit-defined shadow mask lithography. Applied Materials and ACS Interfaces. doi.org/10.1021/acsami.8b19410.

Nanowire networks as a quantum computing platform. (2021) [Online] Eindhoven University of Technology. Available at: https://www.tue.nl/en/news-and-events/news-overview/18-06-2021-nanowire-networks-as-a-platform-for-quantum-computing/

Reimer, M.; (2021). Quantum photonic devices using semiconducting nanowires. Photonics for Quantum 2020. doi.org/10.1117/12.2611219.

Ban, d. and others. (2022). In-situ extrusion of pure-phase InAs-Al Nanowires for quantum devices. Chinese Physics Letters. doi.org/10.1088/0256-307X/39/5/058101.

Patel, M.; (2022). United Kingdom: Five patents in the field of nanotechnology. [Online] Mentor. Available at: https://www.mondaq.com/uk/patent/1151804/five-patents-in-nanotechnology

Wang, S., Z. Chan, and Huang Huang (2017). Mechanical properties of nanowires. advanced science. doi.org/10.1002/advs.201600332.

you, b. et al. (2016). Design and fabrication of silicon nanowires towards efficient solar cells. nano today. doi.org/10.1016/j.nantod.2016.10.001.

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