Quantum network technology

Prof. Stephanie Wehner, Director of the European Quantum Internet Alliance, explains how quantum networking technology and a quantum internet could revolutionize communication and connectivity

The Internet, an intricate network connecting devices from all over the world with classical communication, has profoundly shaped our world. We are now on the verge of a new kind of internet. Imagine an evolution of the internet, intertwining the principles of quantum mechanics with our existing digital technology. This is the vision of a quantum internet, an innovation that promises to redefine our understanding of communication and connectivity.

Working in tandem with our traditional classical internet, a quantum internet would connect quantum devices globally. Such a network would unlock capabilities that are fundamentally unattainable through classical communication alone. Take, for example, Quantum Key Distribution (QKD), an impressive application of quantum communication. QKD allows two distant nodes to create an encryption key protected by the immutable principles of quantum mechanics.

This allows for future-proof secret communications; that is, it is secure even against an eavesdropper equipped with a large-scale quantum computer now or in the future. In a world where data security is paramount, this quantum edge could be very beneficial and is now commercially available in metropolitan areas.

Beyond secure communication, however, we already know of a number of transformative applications that highlight the potential of quantum network technology. The potential is immense, and the vision of a quantum internet is to build a universal quantum network that can be programmed to run any kind of future quantum networking application.

What is a quantum network?

At the heart of these applications are quantum bits, or qubits. Unlike classical bits which exist as 0 or 1, qubits can simultaneously inhabit a state of 0 and 1. Curiously, it is impossible to copy arbitrary qubits. Any duplication attempts can be detected, making them an ideal tool for secure communication. Two qubits can also be entangled, where the entanglement forms an inherently private connection that cannot be shared with anything else.

A quantum network allows the transmission of qubits or, more generally, the creation of entanglement between the nodes of the network (Figure 1). Such nodes can be simple photonic devices that allow only one qubit to be measured at a time or more sophisticated devices.

Unlike quantum computing, where real-world value can only be derived after building a quantum computer capable of outperforming classical (super)computers, the path to user advantage is more gradual in the domain of quantum networking. Simple photonic devices can already unlock applications such as secure quantum communication in metropolitan areas.

Today, quantum communication is commercially available in metropolitan areas (short distances up to 100 km in fiber) when limited to simple use cases enabled by QKD. No long-distance quantum networks are implemented today that allow end-to-end quantum communications and, therefore, secure end-to-end quantum communications.

Ongoing research and development efforts around the world work to advance the quantum network in three directions: (1) distance to connect users in different metropolitan areas and beyond using end-to-end quantum communication; (2) functionality to enable applications beyond secure communication; and (3) affordability to make devices cheaper. Global reach could eventually be achieved using a combination of quantum repeaters in ground-based fiber networks and quantum satellites.

Both are the subject of ongoing research and development efforts. Phases of functionality have been identified (Figure 2) for the development of a quantum internet, where each phase unlocks a larger class of possible user applications. ⁽¹⁾

What can be done with quantum network technology?

Using the stages of functionality as a guideline, we briefly provide more insight into the applications and potential use cases of quantum network technology.

Prepare and measure the phase

This stage contains QKD, which addresses the critical challenge of securing communications in transit and using keys to authenticate access.

Interestingly, many devices capable of performing QKD could, in principle, also be used to provide an advantage in other security-sensitive domains, including, for example, password identification or parsing for the protection of privacy.

Entanglement generation phase

This stage securely unlocks versions of the above use cases with the added assurance that quantum devices are not trusted, a feature known as device independence in quantum cryptography.

Additionally, this stage enables all use cases that take advantage of the fact that entanglement allows for stronger correlations ⁽⁴⁾ when measuring the qubit than allowed in the classical way. It has been shown that there are practical applications for this, allowing remote bridge players to gain an edge. ⁽³⁾

On a more speculative note, it might be interesting to explore whether pre-shared entanglement generated using a quantum network could improve efficiency in other tasks that require coordination, such as high-frequency trading.

Quantum memory stage

This stage can be achieved if the devices connected to the quantum network are quantum processors, i.e. quantum computers capable of storing and manipulating a few qubits. Examples of possible use cases at this stage include secure quantum computing in the cloud. ⁽²⁾

To highlight the breadth of potential use cases, we also point out that a Quantum Internet can combine remote sensors for high resolution imaging. ⁽⁵⁾ This has potential applications in astronomy, getting sharper celestial images, geological exploration, and identifying potential materials in the ground.

Fault-tolerant phase of a few qubits

This stage differs from the last one in that the quality of the qubits in the quantum processor is very high in particular, their quality is protected by fault-tolerant quantum computing.

For example, the Quantum Internet could reduce communication requirements to solve specific tasks. ⁽⁶⁾ This could, for example, enable faster scheduling of appointments across multiple calendars, comparison of data stored in different network sites, or faster image processing in image recognition tasks. Other examples at this stage include enabling data wipe trials. ⁽⁷⁾

Quantum Internet Alliance

The Quantum Internet Alliance (QIA) is a partnership of currently 40 members, including leading players from academia and industry in Europe, to build a prototype Quantum Internet. This prototype network will connect two metropolitan networks via a long-distance backbone.

QIA also provides a platform for Quantum Internet Innovation with connecting opportunities.

References

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6. Rev.mod. Phys. 82, 66, 2010
7. IEEE ISIT 2019, https://doi.org/10.1109/ISIT.2019.8849661