# For a fast and secure future of communications … Learn about quantum networks and how they work

Quantum networks are an important component of quantum computing and quantum communication systems. Information in the form of quantum bits, also called “qubits”, is facilitated between separate quantum processors with no physical links between them.

And quantum processor; It is a small quantum computer that contains quantum logic gates through which a certain number of qubits passes. Quantum networks operate in a similar way to classical networks. The main difference is that quantum networks, like quantum computing, are faster, safer, and better at solving some problems, such as modeling quantum systems.

# What is quantum cryptography?

It can be called “quantum key distribution” as well; It is the essence of quantum communication. Which uses quantum states of particles – such as photons – to form a series of zeros and ones, while any eavesdropping between the transmitter and the receiver will change this thread or key and notice immediately, and until now, the most common quantum key distribution technique uses optical fibers to transmit over a range of several hundred Kilometers, with high stability but large channel loss, while another key quantum switch distribution technique uses the free space between satellites and earth stations for transmissions at the level of a thousand kilometers.

Encryption in general is the process of encrypting data, or converting plain text into scrambled text so that only those who have the correct “key” can read it. Whereas quantum cryptography, by extension, simply uses the principles of quantum mechanics to encode and transmit data in an impenetrable manner.

While the definition appears simple, the complexity lies in the principles of quantum mechanics behind quantum coding, such as;

The particles that make up the universe are inherently uncertain and can exist simultaneously in more than one place or more than one state of existence.

You cannot measure a quantitative property without altering or subverting it.

You can reproduce some of the quantum properties of a particle, but not the entire particle.

All of these principles play a role in how quantum cryptography works.

The development stages of quantum networks and their mechanism of action

Quantum networks will go through various stages of development until reaching their full functionality. Recently, researchers from the Netherlands’ QuTech Institute for Quantitative Research proposed a roadmap towards a full quantitative Internet, detailing six key stages of development determined by the jobs available to the final nodes in the network.

## Zero phase; Pre-quantum networks:

The initial stage is reliable retransmission networks. In these networks, directly connected terminal nodes can distribute quantum keys, and terminal nodes connected to a series of intermediate repeaters can create a secure key, provided they are trusted; They are devices that receive signals and retransmit them as they are or encrypted. This stage can be thought of as a pre-quantum network, or the zero phase, in which no quantitative information is exchanged between the final nodes.

The quantum node must also contain a quantum memory that can store qubit states powerfully, and it should be possible to process quantum information with high precision within the quantum node. Quantum nodes must also be able to communicate over the fibers currently used for the classic Internet.

## The first stage; Experimental quantum networks:

It is the first true quantum stage, in which networks are set up and measured, and complete delivery of qubits is possible allowing, for example, to perform quantum key distribution between any two terminal nodes or secure login to any of them.

## The second phase; Interlocking Distribution Networks:

In which the entanglement is distributed between random nodes in the network. At this stage it becomes possible to implement a device-independent version of the quantum switch distribution, based on entanglement.

The first and second stages can be considered as phases of experimental quantum networks as they allow the use of the initial applications of quantum internet. While the next three phases allow more applications, they can be considered advanced quantum networks.

## The third stage: memory networks:

It requires nodes to be able to hold quantum information in quantum memory for a certain period of time. At this point, simultaneous transmission and quantum computation becomes possible, provided the remote quantum computer is connected to the quantum network.

At this point, implementation of quantum clock synchronization protocols, broadening of the receiving device baseline, and anonymous quantum-encoded transmission becomes possible as well.

## The fourth stage:

To access them, networks must be few qubits, free of errors, local operations, and memory ages so good that the work of a quantum computer connected to the network or distributed by connecting nodes from the network can be performed

## The fifth and final stage; Quantum computing networks:

There is now a complete quantum computer at every point in the final nodes. At this point, all the quantitative applications that we currently envision can be implemented

## Quantum Networks: Between Computing and Communication

Grid-connected quantum computing, or distributed quantum computing, works by connecting multiple quantum processors over a quantum network by sending qubits between them.

Doing so creates the quantum computing cluster, and thus creates more computing potential. Less powerful computers can also be linked in this way to create a single, more powerful processor. It’s a bit like connecting several classic computers to form a computer cluster in classical computing.

And like classical computing, this system is scalable by adding more and more quantum computers to the network. Until now, quantum processors have been separated by short distances.

In the field of quantum communication, one has to send qubits from one quantum processor to another over long distances. In this way, local quantum networks can be connected internally to the quantum internet, which supports many applications, and which derives its power from the fact that by creating interlocking quantum qubits, information can be transferred between remote quantum processors.

Most quantum internet applications require very modest quantum processors. For most quantum internet protocols, such as quantum key distribution in quantum cryptography, it suffices if these processors are able to prepare and measure only one qubit at a time. This is because quantum entanglement can only be achieved between two quantum bits.

This is in contrast to quantum computing, where interesting applications can only be achieved if built-in quantum processors can simulate more qubits than a classic computer.

## Applications and uses of quantum networks

The quantum internet supports many applications, which are enabled by quantum entanglement.

Examples of these applications include quantum key distribution; What we explained above, clock stabilization, baseline extension of telescope connection, plus location verification, secure identification, and binary coding in a noisy storage model. The quantum internet also enables secure access to a quantum computer in the cloud.

In particular, the quantum internet enables very simple quantum devices to communicate with a remote quantum computer in such a way that calculations can be performed without the quantum computer discovering what these calculations are in reality (quantum input and output states cannot be monitored without destroying the computation, but rather the circuit structure is known. Used only).

Secure communications as well; When it comes to communicating in any way, the biggest problem has always been preserving the privacy of those communications. But quantum networks allow information to be created, stored, and transmitted, with a high level of privacy, security, and computational leverage that is impossible to achieve with the Internet today.

By applying the quantum factor chosen by the user to the information system, the information can then be sent to the receiver without the opportunity for the eavesdropper to be able to accurately record the sent information without the knowledge of the sender or the recipient. The quantum information used in quantum networks uses quantum bits (qubits), which can contain both values 0 and 1 at the same time, being in a state of superposition, unlike classic information that is sent in bits and is assigned either 0 or 1.