**Quantum computing has emerged over the last few years as a more efficient and more secure computing option compared to classical computing. The realisation of quantum computers on a large scale is not feasible at the moment, and it may be some time before they are rolled out worldwide. However, if the advances in classical computing over the last couple of decades are any kind of marker, then it may not be long before they are having an impact on everyday society.**

## Complex Computing Algorithms

Complex computing algorithms which can be supported on quantum computers are already in development, and as it stands the software side of quantum computing is not presenting a huge barrier. It is the physical infrastructure, i.e. the hardware, which is currently undergoing a lot of development and is the piece of the quantum computing puzzle which is going to take a long time to develop. The main reason being that it is going to take a long time to find ways of holding the data signals together for long periods of time, so that data can be transferred and stored safely and efficiently. As it stands, the data signals can only be held together for a matter of tens of nanoseconds—so major hardware developments are needed. While these advancements are still needed, the real-world manifestation of quantum technologies will yield computers with much higher efficiencies, that can perform multiple operations simultaneously, with a much higher degree of safety.

## Quantum Bit. The Fundamental Building Block of a Quantum Computer

The fundamental building block of a quantum computer is the quantum bit (qubit). The qubit is much like the classical binary bit found in today’s computers with one fundamental difference. The binary bit can only adopt 0 and 1 states and can only adopt one state at any single time. Qubits can also adopt these 0 and 1 states, but they can also adopt a superimposable 0,1 state which can take either form. This means that qubits can perform operations in both states simultaneously. There are many different materials that have been touted as the best option for making qubits, but semiconductors are currently leading the way.

Where classical bits build up classical computing networks, qubits can be used to build quantum networks. Much like classical computers, these networks run between end nodes, but each qubit in a network needs to become quantumly entangled. When the qubits become quantumly entangled, they are indistinguishable from each other and form a continuum of states. This is a useful mechanism as it means that each network that is looking to transfer data is utilized as a complete system, rather than a series of individual qubits. The transfer and storage of data in qubits, and along quantum networks, is based around manipulating the spin of the electrons in the hardware material and changing the polarization of photons between the qubits.

## Quantum Entanglement Between Qubits

The quantum entanglement between qubits can extend over very long distances and if the properties of a quantum network is measured, the qubits which are entangled to the qubit being measured can also be analyzed. This means that individual quantum networks can be built with different values and properties, but each of the qubits in a single network hold the same information. Data can also be transferred between locations through quantum teleportation, which is a phenomenon similar to quantum entanglement and manipulates the electrons and photons to transmit the data. As mentioned, these quantum networks are capped at either end by nodes. These end nodes can be made from a number of things, including a quantum processor of at least a single bit, a beamsplitter, photodetector, telecommunication laser, quantum logic gate, or an ion trap.

To build up a quantum computer, there is other physical infrastructure that needs to be implemented alongside the qubits. Two of the key pieces of infrastructure are the communication channels between qubits and quantum repeaters. The communication channels act as a pathway between qubits where single photons are sent down either a free space network or a fiber optic cable. Quantum repeaters are a series of components that are utilized in the communication channels to prevent the signal from weakening or completely breaking down as the data is being transferred. Given the complexity of the signal, the efforts to keep the signal steady in quantum networks is much harder than in classical networks, so more components are required.

## Conclusion

All these different functions, from the qubits, to the infrastructure, to the quantum algorithms are key to realizing quantum computers. While aspects are already being trialled, there are other parts of quantum computing which are going to take time to become usable in real-world applications. But there is the potential for the computing industry to be disrupted if quantum computing lives up to its potential.

## Sources and Further Reading

- Semiconductor Qubits for Quantum Computation - Technische Universität München
- Semiconductor Devices for Quantum Computing - American Physical Society
- Quantum Computing Lecture 1 - Cambridge University
- “Quantum Internet: from Communication to Distributed Computing!”- Caleffi M. et al,
*NANOCOM '18 Proceedings of the 5th ACM International Conference on Nanoscale Computing and Communication*, 2018,** **DOI: 10.1145/3233188.3233224
- “Quantum networks: where should we be heading?”- Sasaki M.,
*Quantum Science and Technology, *2017, DOI: 10.1088/2058-9565/aa6994
- “Building the quantum network”- Elliot C.,
*New Journal of Physics*, 2002, DOI: 10.1088/1367-2630/4/1/346

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