Colab Aims to Create a Secured Quantum Internet Using Quantum Key Distribution

October 18, 2021 by Abdulwaliy Oyekunle

Researchers and companies alike are investing time into quantum networks/internet. However, what is this technology, how is it secured with quantum key distribution, and what are TB Group and Toshiba creating?

Recently, the discussion of how researchers are addressing the challenges of developing a quantum internet has been floating around. Despite the benefits presented with the possibilities of creating a quantum internet, a challenge still resides in its security. However, one way to help surmount the security challenges in a quantum network is to use quantum cryptography to provide security for encrypted traffic.


One example of a quantum network.

One example of a quantum network. Image use courtesy of Quantum Xchange


In other words, quantum key distribution (QKD) based cryptography has researchers and companies adopting this form of security to build a safe quantum internet. One recent example comes from BT Group and Toshiba, who are hoping to use this security protocol for a quantum network in the world’s first quantum-secured commercial metro network across sites in London.

Though this concept of a quantum internet is interesting and has the potential to benefit society, there is still a lot to consider, especially concerning infrastructure and security. 

This article will address what roles quantum cryptography plays in enabling an ultra-secure quantum network and what a typical quantum internet infrastructure looks like.


Quantum Key Distribution Secures Quantum Communication

From secure communication between remote quantum computers to the development of quantum sensor networks to gather quantum data, quantum internet introduces our world to an advanced means of communication between two or more stations.

While the classical internet transmits binary bits of ones and zeros, taking only one of the values at a time, a qubit that can be a superposition of 0 and 1 simultaneously is transmitted as quantum data in a quantum network.

In quantum communication, a single photon (which carries the encrypted bit) is emitted and channeled through an optic fiber (which is regarded as the quantum channel) to a receiver. Quantum cryptography protocols, based on the Heisenberg uncertainty principle, are used to securely transmit the photon successfully in such a way that an eavesdropper does not know the contents of the data.


Schematic diagram of the QKD-based Cambridge's quantum network.

Schematic diagram of the QKD-based Cambridge quantum network. Image used courtesy of Dynes et al


For instance, the BB84 quantum key distribution protocol employs the polarization states of the photons to encode bit values over the optic fiber quantum channel. 

Polarization states for a 0 may either be 135° or a horizontal state, and a 1 may either be 45° or a vertical state. A randomly selected polarization state corresponding to a photon is then emitted over the quantum channel. 

The receiver employs filters to detect the states of the received photons and records the qubit values generated after detection. A rectilinear filter correctly detects horizontal and vertical states, while a diagonal filter detects the 135° and 45° states.

Once the transmission is completed, both the emitter and receiver announce the states they used to send and receive the photons, which is done over a public channel (say, classical internet). 

Then the emitter gives the receiver the polarized state of the photons, thus matching the filter state by which they were received. Finally, all photons recieved with the wrong filter will be discarded.

In a BB84 quantum key distribution protocol, errors in the channel are attributed to the actions of the eavesdropper. Key distillation is further done to mitigate the effect of the errors.


State-of-the-art Quantum Networks

In general, the BB84 protocol is widely used among researchers building quantum networks. The protocol is adopted in the state-of-the-art quantum network infrastructure, such as the Cambridge Quantum Network extending from Cambridge to Bristol. 

The Cambridge Quantum Network utilizes a QKD system that achieves secure bit rates of up to 3 megabits per second over short distances.

The quantum network built by researchers at Toshiba Research Europe Limited can support many users with key rates up to 1000 bits per second.

Scalable quantum computers and networks run sophisticated application protocols. Thanks to simulation software to test and run quantum networks before deployment. Like in the Cambridge Quantum Network, the researchers simulated the BB84 protocol with two decoy states to choose a practical value (0.4 photons per pulse for strong decoy states and 10-4 photons per pulse for the weak decoy states) for the intensities of the signal before deployment.

Furthermore, researchers have recently introduced a simulation software called SeQUeNCe, which is capable of running quantum network prototypes that capture the breadth of current and future hardware technologies and protocols.


An abstraction of a quantum network infrastructure featured in SeQUeNCe quantum network simulator.

An abstraction of a quantum network infrastructure is featured in the SeQUeNCe quantum network simulator. Image used courtesy of Wu et al


The SeQUeNCe is optimized to perform a scalable quantum network's entanglement management, resource management, and network management functions. 

Typical hardware requirements of a quantum network that can be supported by this tool include quantum channels, classical channels, quantum gates, and photon detectors. Plus, the tool features quantum memories which is important for long-distance quantum communication.


More Quantum Networks Infrastructure Ahead

Apart from SwissQuantum, the first international QKD-based network built in the Geneva metropolitan area, BT and Toshiba aim to develop the world's first quantum-secured metro network that will connect three different sites: London's Docklands, the City and the M4 Corridor. All situated in London.

The collaboration between BT and Toshiba aims to serve many users across a wide metropolitan area. While BT will provide the quantum network infrastructure services, Toshiba will provide quantum key distribution hardware and key management software.

Customers could enjoy quantum-secured network services which protect their data from retrospective attacks with a quantum computer, says Taro Shimada, Corporate Senior Vice President and Chief Digital Officer at Toshiba Corporation. 

This collaboration is just one step towards making the quantum internet a more widespread technology. It will be interesting to see what develops next. 



Interested in other quantum-related news? Learn more in the articles down below.

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