Understanding How Quantum Technologies Can Work

Quantum technologies are an area, once manifested, that could change the face of many technology-based applications. Although quantum technologies are not quite there yet, scientists have already managed to create devices that can transmit data using quantum networks, albeit for a matter of nanoseconds at low temperatures. Nevertheless, gains are being made—with semiconductors currently leading the way as the fundamental building blocks—and if you look at the huge advances made in classical computing technologies over the past few decades, then quantum technologies might not be as far away as many think.

Quantum technology will be valuable for many reasons, especially for anything that uses a computer chip, as it will enable more operations to be performed simultaneously—and at a greater speed than modern-day computers—while providing an extra layer of encryption that is much needed in today’s online world.

Behind any quantum technology is the quantum bit—otherwise known as a qubit—and is similar, yet so very different, to a classic computing bit. Qubits are the building blocks of quantum networks, much like classical bits are in classical networks. Classical computing bits—known to many as binary bits– can take one of two forms. These are a 1 and 0. Qubits can also take the form of a 1 or 0, but there is a third form that is not possible with classical bits, and that is a superimposable form that can take the form of either a 1 or a 0. Because the superimposable form can take either form, operations can be performed in both values simultaneously—something not possible with classical networks. It is one of the fundamental reasons why quantum networks will be able to process multiple operations at much higher speeds than classical networks.

Figure 1: Qubits, the building blocks of quantum networks, can come in three forms and possess infinite value. (Source: Production Perig/Shutterstock.com)

Each qubit can possess an infinite value within each of the three forms. This leads to a continuum of states where each qubit becomes one and indistinguishable from each other. Although the individual qubit uses the spin of electrons and polarization of photons to store data, they can become entangled, which makes them act as a unified system. This means that each quantum network is described and used as a complete system, rather than a series of qubits.

Quantum entanglement is an important phenomenon in quantum networks. Electrons, photons, atoms, and molecules can all become entangled in these networks. The entanglement within a quantum network also extends over long distances. When one part of the quantum network is measured, the properties of the corresponding entangled qubit(s) within that specific network can be deduced as a definitive value. This enables many networks to be built up, all of which have different values and properties, but where all the qubits in a single network share the same information.

Quantum teleportation is another phenomenon that enables quantum technologies to function, and is similar in nature to quantum entanglement. Quantum teleportation is the process where the data and/or information held in the qubit—which is held there by the electrons spinning up or down, and by polarizing the photons in a vertical or horizontal orientation—is transported from one location to another without transporting the qubit itself.

Most qubits become entangled in these networks; however, if doubt exists that they haven’t become entangled, they can be tested using coincidence correlation. Coincidence correlation assumes that an entangled network can only emit one photon at a time. You can use multiple photodetectors to see how many photons are emitted by a single network. If more than one photon is recorded at any one time, then you can assume that the quantum network is not a single-photon system, and therefore not entangled.

The materials that make up the qubits are an essential part of establishing a quantum network. The quantum system is formed by manipulating physical materials, so the properties and characteristics of the materials used to build a quantum network is a major consideration. For any material to be considered as the building block of a quantum technology, it needs to possess long-lived spin states, which it can control, and be able to operate parallel qubit networks.

Many physical parts also go into designing a quantum network. One of the key features the quantum system requires is an arrangement of interconnected communication lines between each network. Just like in classical computing, these communication lines run between end nodes. These nodes are representative of the information held within an individual quantum network, and this becomes more important for larger and/or complex quantum networks where a lot of different types of information are held within the quantum system. These end nodes can take many forms, although the most popular choices at the moment are:

• Beamsplitters
• Photodetectors
• Telecommunication lasers
• Quantum logic gates
• Ion traps

Two other physical components are crucial if a quantum network is to function as it should. These are the communication lines and quantum repeaters. The physical communication lines currently take two main forms, which are fiber-optic networks and free-space networks, and both work differently. Physical communication lines made from fiber-optic cables send a single photon by attenuating a telecommunication laser, and the path of the photon is controlled by a series of interferometers and beam splitters before it is detected and received by a photodetector. Free-space networks, on the other hand, rely on the line of sight between both ends of the communication pathway. As it stands, both can be used over long distances, but free-space networks suffer from less interference, have higher transmission rates, and are faster than fiber-optic networks.

The other important component is the repeater, which ensures that the quantum network does not lose its signal or become compromised because of decoherence—which is the loss of information due to environmental noise. It is a straight-forward process in classical networks, because an amplifier simply boosts the signal. For quantum networks, it is much trickier. Quantum networks need to employ a series of trusted repeaters, quantum repeaters, error correctors, and entanglement purifying mechanisms to test the infrastructure, to keep the qubits entangled, to detect any short-range communication errors, and to minimize the degree of decoherence in the network.

An extra layer of security can be incorporated into quantum networks through quantum key distribution, which utilizes the principles of quantum mechanics to perform cryptographic operations. This will be a particularly useful tool for when two people are communicating via a quantum network, or data is being transmitted from location to another. The encryption process will utilize randomly polarized photons to transmit a random number sequence. These sequences then act as keys in the cryptographic system. The theory behind these cryptographic systems is that they will use two networks—a classical channel and a quantum channel—between two different communication points, where both channels play specific roles. The classical channel is there to perform classical operations and is a way of seeing if anyone is trying to hack into the network. However, the qubits containing the data will be sent over the quantum channel, which means that the classical system can be hacked, but the hackers will not obtain any information—as no information would exist in that channel. The way that these systems will be able to tell if a network has been hacked is down to the correlation of the signal. Classical networks are highly correlated, and if any imperfections occur between the source and the receiver in the channel, then the system will know if a hack has been attempted.

Although the realization of quantum technologies in everyday systems might be a while off yet, the potential is there for these technologies to revolutionize the computing and communication spaces. The ability for quantum networks to become one and be transmitted over long distances has many advantages over classical systems, which include the potential for faster data transmission types, the ability to perform multiple operations simultaneously, and for highly encrypted data communication channels.