Nanowires are virtually one-dimensional objects with only one dimension measuring more than a few nanometers. Manufactured nanowires have numerous nanotechnology applications, including in quantum devices like quantum computers.
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What are Nanowires?
Nanowires are a class of nanostructure, along with nanoparticles, nanotubes, and thin films. Nanowires are tiny wire shapes whose diameter measures between 0.1 and 100 nanometers and can be thousands of times longer than they are thick.
Nanowires are made out of many different types of material depending on their purpose and industrial use. For example, superconducting nanowires are synthesized from YBCO composites, metallic nanowires from silver, gold, and platinum, semiconducting nanowires made of silicon, and insulating nanowires made from silicon oxide or titanium. It is also possible to produce molecular nanowires by repeating organic molecular units (like DNA) or other inorganic molecules.
Due to the recent development of manipulation techniques over the past couple of decades, it is now possible to create complete mechanical characterizations of nanowires. Manipulation equipment used to achieve this includes the atomic force microscope (AFM), scanning electron microscope (SEM), and focus ion beam SEM (FIB-SEM). The introduction of micro-electromechanical systems (MEMS) technology to electron microscopy has also played a part 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 making good candidates for advanced composite additives.
Nanowires in Quantum Devices
At such tiny proportions, nanowires behave according to the peculiar laws of quantum mechanics, making them suitable for applications in quantum devices.
Quantum devices are any technology with at least one feature that manipulates phenomena of quantum mechanics. Quantum computers, which use quantum superpositioning to encode qubits of data, are one example of a quantum device.
Quantum computers encode qubits (instead of bits, “binary units”) with information. These systems manipulate quantum mechanical phenomena such as superpositioning and quantum entanglement to process more data simultaneously than conventional binary computers are capable of. The result is, in theory, much faster computing power in much smaller processor chips.
Quantum dots are used as the qubits in quantum computers. Because they are quantum particles, phenomena like quantum entanglement and superposition can be induced or manipulated in them.
At present, the majority of quantum devices that employ nanowires to manipulate features of quantum mechanics are quantum electrical devices.
However, nanowires are also under investigation for use in optical quantum devices. Nanowires could be employed as photon ballistic waveguides in well photon logic arrays (a kind of optical computing) that use quantum dots to encode information. Photons are sent through the nanowire, with electrons traveling alongside them on the outside shell.
In this example, the nanowires acting as photon waveguides are crossed over one another, making a quantum dot at their juncture. Quantum dots are quantized semiconductor particles with important applications in quantum computing, where they can be encoded as qubits.
Quantum dots formed this way can be used to make pairs of photons exhibiting quantum entanglement. In this phenomenon, two quantum particles (photons in this case) become entangled, so physical stimuli affecting one particle also appear to affect its pair even when they are physically separated.
Currently, quantum computing is limited by the extremely unstable nature of quantum states. It is difficult to create a controllable array of qubits and reliably maintain their quantum states in normal conditions, and many practical quantum computers need temperatures near 0 K to operate.
One proposed quantum computing method relies on topology to make qubits, and is theoretically much more stable. The Majorana state of a particle with an antiparticle can hold quantized 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 practical topological quantum computer.
In 2022, scientists grew indium arsenide (InAs) nanowires measuring only 20 nanometer across using molecular beam epitaxy. This method can be applied to build relatively highly stable topological quantum computers.
Future Outlook: Maturing Technology
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 entirely) limited to research. No company has yet made a commercially viable quantum computer, for example.
Recently, global technology firm Intel sought intellectual property (IP) protection for 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 locate the quantum dots in space with great precision.
Improved spatial accuracy would provide improved quantum dot manipulation control and makes electrostatic controls more responsive. As a result, Intel engineers should have more design freedom and flexibility in terms of where to put electrical connections and integrate quantum dots in 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 approaching maturity.
References and Further Reading
Dumé, I., (2022). Ultrathin nanowires could be a boon for error-resistant quantum computing. [Online] Physics World. Available at: https://physicsworld.com/a/ultrathin-nanowires-could-be-a-boon-for-error-resistant-quantum-computing/
Enrico, A., et al. (2019). Scalable Manufacturing of Single Nanowire Devices Using Crack-Defined Shadow Mask Lithography. ACS Applied Materials & Interfaces. doi.org/10.1021/acsami.8b19410.
Nanowire networks as a platform for quantum computing. (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 shaped semiconductor nanowires. Photonics for Quantum 2020. doi.org/10.1117/12.2611219.
Pan, D., et al. (2022). In Situ Epitaxy of Pure Phase Ultra-Thin InAs-Al Nanowires for Quantum Devices. Chinese Physics Letters. doi.org/10.1088/0256-307X/39/5/058101.
Patel, M. (2022). UK: Five Patents In Nanotechnology. [Online] Mondaq. Available at: https://www.mondaq.com/uk/patent/1151804/five-patents-in-nanotechnology
Wang, S., Z. Shan, and H. Huang (2017). The Mechanical Properties of Nanowires. Advanced Science. doi.org/10.1002/advs.201600332.
Yu, P., et al. (2016). Design and fabrication of silicon nanowires towards efficient solar cells. Nano Today. doi.org/10.1016/j.nantod.2016.10.001.