The internet is an inescapable part of our lives. A quantum internet would build on that, adding new capabilities and security.
Scientists have already made significant strides in developing quantum networks. They have demonstrated secure quantum key distribution (QKD) over long distances using existing fiber cables and satellites.
They have also tested quantum repeaters, the component technology needed for scaling a quantum network. Quantum repeaters rely on the phenomenon of entanglement to transmit quantum signals over long distances.
The quantum internet will someday link devices that send, compute and receive information encoded in quantum states. It won’t replace the modern or “classical” internet, but it will add new functions such as quantum cryptography and quantum cloud computing that promise unimaginably high speeds and unprecedented security.
Quantum information is encoded in quantum bits, or qubits, that can be in two different states at the same time — a phenomenon known as superposition. The quantum internet will rely on this to transmit information between distant locations, using quantum teleportation that exploits the particles’ entangled state. Such a network could offer perfect security, meaning it would be impossible to hack, revolutionizing fields such as finance, national security and healthcare, Spentzouris says.
Physicists have already made significant progress towards building such a quantum internet. Last year, researchers in Bristol created an on-demand quantum light source in silicon, a milestone that may help lower the cost of such networks. They also tested quantum repeaters, a key technology that would enable long-distance transmission of qubits, which require extremely low optical loss to be transmitted over large distances. The repeaters work by measuring a photonic signal and then sending out a stronger version of it. Optical losses can be minimized by using single-photon sources like nitrogen voids in diamonds, and by transmitting the signals over low-loss optical fiber.
Quantum mechanics imposes new constraints that have no analog in classical networks. Phenomena like no-cloning, quantum measurement, and entanglement require a network paradigm shift to leverage their specificities for breakthrough applications.
One of the biggest challenges is to create a network that can reliably send quantum information over long distances in the form of photon sequences. Scientists have made significant progress in this regard. For instance, Samsung’s Galaxy Quantum smartphone uses a single photon source to enable QKD and provide security with unbreakable codes. Nevertheless, this technology is not yet ready to serve as the backbone of a quantum internet.
In order to increase the efficiency of such a network, scientists are working on quantum repeaters, component technologies that would allow the transmission of entangled photonic states over long distances. However, these components must be highly efficient since the fidelity of entangled states degrades rapidly over physical links. They must also be designed to use the lowest possible energy per bit, a key requirement for cost-effectiveness.
Other key challenges include identifying the network boundaries between quantum and classical networks, and connecting quantum networks with different implementation basis. Scientists are also exploring ways to optimize the transmission of single photons over long distances. One such technique relies on nitrogen vacancy centers in diamond crystals (known as NV centers). This is an attractive option because it can be generated at low cost and enables point-to-point communication over large distances.
It’s possible that one day, we could send data encoded in quantum states across a network of devices — both on our laptops and in the cloud. This would be accomplished by leveraging the weird properties of quantum particles, such as their ability to be in two well-defined states (clockwise and anticlockwise spinning, for example) or entangled — sharing a single quantum state even when separated by vast distances.
The technology behind QKD is still very new, and current experiments are limited by a number of factors, including the fact that quantum signals get lost or scattered when sent over long distances like optic-fibre cables. But researchers are working hard to overcome these challenges by incorporating more elements of quantum theory, such as the phenomenon of entanglement.
In addition to developing the physical infrastructure, scientists will need to develop a way to store and transmit qubits from a quantum device to another. These capabilities are important because they enable the creation of quantum internet stages that can deliver on the promise of secure communications and computing.
Governments can play a key role in this effort by helping create the training and content needed to prepare for the quantum revolution. This is important because, unlike interstate highways, wireless spectrum or air traffic control, quantum is a highly disruptive technology that will require all public sectors to work together to ensure that it is successful.