Today, the conventional internet enatils a coherent stream of photons traveling down a fiber-optic wire, carrying a logical one or zero somewhere around eighty percent the speed of light. Tomorrow, a pair of entangled photons—each called qubits—are both one and zero (superposition) and send data in near-instantaneous time. That’s “quantum internet.”
The quantum system used by Delft University to connect “users” together in an “ultra-secure” network environment. Image used courtesy of Nature
The so-called quantum internet exchanges information by maximizing coordination and entanglement and interrogating the state of the qubit. This next-generation internet is described as “ultra secure,” owing to the nature of entanglement itself. Once fully entangled, qubits cannot be read by any third-party attempting to eavesdrop on a communication channel.
But just as there are many obstacles to make quantum computers a reality, research institutions worldwide face many roadblocks to bring the quantum internet to life.
Challenges of a Quantum Internet Channel
When considering the manifold applications of quantum computers, synchronicity and privacy are chief concerns. Any application requiring the alignment of time, such as satellite-to-earth communications, will benefit from maximum coordination. In simplest terms, maximum coordination allows the two entangled computers to know the exact state reference of the other.
However, there are several challenges associated with this technology, including:
- Entanglement over distances greater than a few hundred kilometers
- Linking more than two users together in a network while maintaining entanglement
- Maintaining coherent control of single photons
- Developing the hardware to actually facilitate quantum networks
The last three of these roadblocks have recently been addressed by researchers at three Universities: Delft University (Netherlands), the University of Cambridge, and Purdue University, respectively.
A Three-unit Quantum Network
At the Delft University of Technology, Netherlands, researchers have successfully created a three-way entangled network between three “users” by embedding one entangled pair in a “memory” element.
The research at Delft University created a three-party entanglement using a nitrogen atom inside a synthetic crystal structure to create a memory of the first entanglement. Image used courtesy of Nature
The qubit is stored inside a physical medium for up to one minute. This precursor network has the potential to allow data exchange between three users in an ultra-secure environment guaranteed by the laws of quantum mechanics.
Controlling a Single Electron in the Cloud
Controlling the state, or destiny, of a single photon is a daunting task. This is especially true when the photon is released into the “wild”—a physical network.
Researchers at the University of Cambridge have been able to direct the state of a quantum dot in the “cloud” by using a laser to communicate to an electron that has been inserted into the quantum structure. This brings order to the chaos of freely roaming particles because the nuclei shifts in response to the excited electron.
The schematic for the laser modulator used to induce “ordered chaos” on the 100,000 nuclei by controlling the spin of a single electron in the cloud. Image used courtesy of Nature
“We don’t have a way of ‘talking’ to the cloud and the cloud doesn’t have a way of talking to us,” says Mete Atature, the lead researcher from Cambridge’s Cavendish Laboratory. “But what we can talk to is an electron: we can communicate with it sort of like a dog that herds sheep.”
A Quantum-ready Hardware Switch
Another issue with the quantum internet is hosting multiple users on a quantum network with dissimilar bandwidth requirements sharing a quantum channel. Researchers at Purdue University are seeking to address this issue by varying the frequency allotment of users to alter the rate of entanglement between the users.
They have also “flexed the grid” of the network, much like networks do today to allocate additional bandwidth when needed, say for streaming future media.
Adaptive bandwidth network switch allows multiple users to share optical channels with varied slices of frequency and total used bandwidth. Image used courtesy of OSA Publishing
“We show a way to do wavelength routing with just one piece of equipment—a wavelength-selective switch—to, in principle, build a network of 12 to 20 users, maybe even more,” said Andrew Weiner, an ECE professor at Purdue.
A Protocol for the First Quantum Network
Researchers at the Kavli Institute of Nanoscience, Delft University of Technology, are tackling the early questions about what a quantum network protocol would look like.
A quantum network stack would run parallel to classical networks, extending the functionality of existing networks with enhanced cryptography and synchronization. Image used courtesy of Arxiv
In order to address the issues of photon decoherence and signal fidelity, the researchers investigated the concept of a repeater at some point in the network. Engineers familiar with the difficulties of sending PCIe data at high speeds will have experienced data decoherence.
A conceptual quantum repeater, overcoming the no-clone theorem by swapping entanglement states midway. Image used courtesy of Arxiv
A traditional electronic repeater samples the incoming data, amplifies it, and re-broadcasts a copy of that binary data to the next node in the network. This works well for data transmitted in traditional mediums. It’s different for quantum particles, however.
By performing an entanglement swap at a repeater, the state of the photons can be maintained without the loss of data and without having to clone the data, which is impossible in the quantum domain.
The proposed network stack capable of quantum communications. Image used courtesy of Arxiv
The end goal of all of this research is to reliably send qubits over long distances with high-fidelity, thereby creating a local network.
The Next Step in Advancing Quantum Networks
The next research step is to decipher the state of a single photon in a “cloud” of photons traveling along the network before processing it through a switching device to ensure it arrives at its destination.
It may be a few more years before that first distributed quantum network goes online. Strangely enough, when that happens one could argue that the system is both online and offline at the same time.
What are your thoughts on the development of quantum-level technology? Leave your comments below.