Quantum Repeaters: Building the Global Quantum Internet

Quantum Repeaters Can Power the Global Quantum Internet

A new chapter in information technology is beginning. Up until now, the data revolution has unfolded based almost entirely on what a physicist would call a classical model of information. Just as there are two models of physics, classical and quantum, computing has two versions. Quantum computers are machines that use quantum physics to store data and perform computations and the analogous quantum internet is in the making. This can be extremely advantageous for certain tasks where they could vastly outperform even our best supercomputers.

The field of quantum technology has witnessed remarkable advancements many of which push the boundaries of what is possible in computing, communication, and information processing. Quantum networking should be added to list of world-altering technologies that are right now advancing faster, perhaps, than society can deal with reasonably. One of the most promising and captivating frontiers in this domain is the development of a quantum repeater which may make this all a reality sooner than expected.

The idea of a metaverse is abstract and varies depending on whom you ask, but a quantum internet is a physical reality that can be achieved. Progress toward 'the Metaverse' is still hard to measure or to even define.

With the potential to revolutionize global communication, the quantum internet promises secure and efficient transmission of information applying the principles of quantum mechanics. Thankfully, you don't need a course in physics to understand the quantum internet.

entanglement distribution localized in red and blue
Entangled particles. H. Ritsch/University of Innsbruck

In this article, we will delve into the intricacies of the quantum internet and quantum computing (QC), exploring its key components, underlying principles, and its transformative impact on various sectors. Let's embark on this journey into the world of quantum communication and discover how it can reshape the future starting with its components.

Bridging the Gaps With Quantum Repeaters:

At its core, the quantum internet aims to establish a global network of interconnected quantum computers, quantum processors, and other quantum-enabled devices. It will facilitate the transmission of quantum bits or qubits, the fundamental units of quantum information. Unlike classical bits, which can represent either 0 or 1, qubits can exist in a superposition of states, enabling exponential parallelism and computational power. What it means is that in situations where there are a large number of possible combinations, quantum computers can consider all of them simultaneously. Examples include trying to find the prime factors of a very large number or the best route between two places. There are countless ways there but only one desired outcome.

classical bit vs qubit or quantum bit
Classical Vs Quantum bit (Qubit)

This opens up new frontiers for quantum computation and communication. In fact, the notion a thinking computer is almost inconceivable without quantum computing. Quantum networks will serve as the backbone of an inevitable global quantum internet, enabling the transmission of quantum information across vast distances.

These networks are designed to harness the principles of quantum mechanics, allowing for secure and high-speed communication. By leveraging quantum phenomena such as entanglement and superposition, quantum networks pave the way for unprecedented capabilities in information transfer and processing.

The quantum internet is a network of interconnected quantum computers that enables the transmission, computation, and reception of information encoded in quantum states. It is important to note that the quantum internet does not aim to replace the existing classical internet but rather offers additional functionalities such as quantum cryptography and quantum cloud computing.

While the complete implications of the quantum internet are still being explored, several applications have been theorized, and some are already in use, such as quantum key distribution. The timeline for deploying a global quantum internet on a large scale remains uncertain, but researchers estimate that interstate quantum networks will be completed within the United States in the next 10 to 15 years but that time span is shrinking fast.

a globe in a computer controlled environment colorful
"World Entangled" Rendered in Midjourney

What Will the Quantum Internet Be?

The quantum internet is a highly sought-after network that connects quantum computers, allowing for the transmission, computation, and reception of information using quantum technology. Its purpose is not to replace the current internet but to exist alongside it, addressing specific problem types.

What are Quantum Computers:

Powering the Future: Quantum computers, with their immense processing capabilities, form a critical component of the quantum internet ecosystem. These computers leverage the principles of quantum mechanics to perform complex calculations and solve problems that are beyond the reach of classical computers. Harnessing phenomena such as quantum entanglement and superposition, quantum computers have the potential to revolutionize fields such as cryptography, optimization, and drug discovery.

How does the Quantum Internet work?

For example, one quantum state used for encoding information is the property called "spin," which represents the intrinsic angular momentum of an electron. Manipulating this spin allows for the encoding of information in the electrons themselves, leveraging a combination of possible states. Qubits can exist in a superposition, simultaneously representing both 0 and 1, as well as neither.

This enables quantum computers to process information in a fundamentally different way, offering the potential to solve complex problems more efficiently. How to move these qubits across vast distances is now solved with repeaters, scalability is the issue.

About Qubits:

The delicate nature of quantum states poses a challenge for qubits, as they are susceptible to disruptions caused by external factors like vibrations or temperature fluctuations. When a quantum state is disturbed, it loses the valuable information it carries. To mitigate this issue, many quantum computers require isolation and cooling to near absolute zero, resulting in significant costs.

qubits explained quantum internet computing


An alternative approach to cryogenic storage involves utilizing a different type of qubit that operates at room temperature. One promising candidate is the defect spin qubit, which can be implemented using exceptionally robust materials like diamond or silicon carbide. These materials are engineered with specific defects in their molecular structure, and quantum information is stored within molecules present in these defects.

Notably, David Awschalom, the Liew Family Professor in Molecular Engineering and Physics at the University of Chicago, as well as a senior scientist at Argonne National Laboratory, has achieved remarkable advancements in this domain.

For instance, in February 2022, Awschalom and his team achieved a significant breakthrough by maintaining the quantum state of a spin defect qubit for an impressive duration of five seconds at a temperature of 5 Kelvin or five degrees above absolute zero. This accomplishment set a new record for this type of device and also demonstrated the ability to retrieve information stored in the qubit as needed, marking a substantial step forward in the field of quantum computing.

By leveraging such advancements, researchers are making notable progress in developing qubits that can function effectively at room temperature, thereby alleviating the need for costly cryogenic environments and expanding the feasibility of practical quantum computing applications.

Optical Fiber:

Enabling Quantum Communication: Optical fiber serves as the medium for transmitting quantum information in the form of photons over long distances. The low-loss properties make optical fibers an ideal choice for maintaining the fragile quantum states of photons. Furthermore, advancements in fiber optic technology and the development of specialized fibers, such as those designed for telecom wavelengths, have significantly contributed to the progress of quantum communication.

When it comes to transferring qubits from one location to another, particularly in the early stages of development, the use of fiber optic cable has been error-ridden.

In recent years, two primary options have emerged as the most promising contenders: satellite transmission and fiber-optic cable. Between these two choices, fiber optics have emerged as the more cost-effective and widely available solution versus satellites.

Single Photons:

Single photons like the ones entangled like envisioned above are the fundamental carriers of quantum information in the quantum internet. These are particles of light used to encode and transmit qubits between different nodes in a quantum network. Generating just one photon reliably and efficiently is a significant technological challenge that researchers are actively addressing.

Because a photon and an anti-photon must be entangled in physical space, the distribution of entangled particles matters.  Various sources, such as quantum dots and other advanced technologies, are being explored to achieve the controlled generation of single photons with high fidelity and scalability. These efforts aim to enhance the performance and reliability of quantum communication systems and contribute to the development of a robust quantum internet infrastructure.

Quantum Repeaters:Extending Quantum Reach:

In quantum communication, repeater nodes play a crucial role in extending the reach of quantum signals. These quantum nodes enable the distribution of entanglement across long distances by employing quantum error correction techniques.

Overcoming Long Distances in Quantum Communication

The successful realization of a quantum internet hinges on the ability to transmit quantum information over long distances. Conventional communication channels face challenges when it comes to maintaining the delicate quantum states of particles over extended fiber optic links. However, recent breakthroughs in the field have paved the way for long-distance quantum communication by employing techniques such as entanglement swapping and photonic quantum repeaters.

Expanding beyond a regional network, like the ongoing development in Chicago, presents a significant challenge in the amplification of quantum signals. Unlike classical signals, quantum states are inherently delicate, making the task of signal amplification particularly difficult. In the classical internet, when a signal weakens, repeaters can capture and retransmit it to maintain its strength. However, the situation is different in the quantum realm due to the "no-clone theorem," which dictates that attempting to duplicate an entangled photon will result in its destruction.

qubit representation in colorful swirl the quantum internet
A representation of a Qubit in color.

To overcome this obstacle, researchers are actively exploring various approaches to repeat a quantum signal without compromising its integrity. One promising avenue involves the deployment of quantum memories, as suggested by Tian Zhong, an assistant professor at the Pritzker School of Molecular Engineering (PME) at the University of Chicago. Quantum memory has the potential to shield quantum information from decoherence, acting as quantum relays that preserve qubits until they reach their intended destination. The implementation of such a system could theoretically enable global quantum communication by ensuring the integrity of qubits throughout their journey.

As quantum information tends to degrade quickly due to environmental factors, repeater nodes serve as intermediate points that refresh and amplify the fragile quantum signals. These nodes employ advanced techniques such as entanglement swapping and entanglement distillation to overcome the limitations imposed by noise and signal loss.

How far off is the Quantum Internet?

While a sustained large-scale quantum network has not been achieved yet, significant progress has been made. It is the construction of a worldwide quantum information network. Researchers have successfully transmitted entangled photons between a satellite and ground stations, showing the potential use of satellites in quantum networks. Additionally, experiments involving quantum entanglement over several miles and the establishment of a quantum network testbed have been conducted.

Entanglement is essential to the workings of quantum computers, which can in theory solve problems no conventional computer ever could. But they have limitations classical computers don't have so the future internet will likely be a hybrid of both.

In January 2020, a 54-mile quantum loop was tested using an existing fiber-optic cable. This project demonstrated the core functionality required for a quantum network line, and subsequent expansions have increased the scale of the network. The extended Chicago network, comprising six nodes and 124 miles of optical fiber, represents a significant step towards larger, interstate quantum systems.

Fibers or Satellites?

The Chinese made a satellite for sending quantum data. The experimental satellite contains a quantum key communicator, quantum entanglement emitter, entanglement source, processing unit and a laser communicator. It will orbit at an altitude of 1,000km and is expected to live two years. We already know from this research fiber optic networks, not satellites, will ferry the majority of qubits. So far, it appears, that optical fibers will be the scaffolding.

Other Countries are Racing Toward the Global QI

Other countries, however, are vigorously pursuing the technology as it will benefit the first to reach it the most. Austria is perhaps in the lead with a group from the University of Innsbruck making major advances. Being hesitant to call it an arms race since the AI arms race began, this is more of a collaborative effort being a global network. Russians along with scientists from Sweden and the US have made progress by returning a quantum computer to a state a fraction of a second in the past. By doing this, they have one observation that may violate the second law of thermodynamics.

"We have artificially created a state that evolves in a direction opposite to that of the thermodynamic arrow of time," Gordey Lesovik


Lesovik, a Russian quantum physicist from the Moscow Institute of Physics and Technology announced the finding in a press release. A multi-qubit processor or repeater with low error running quantum algorithms is around the corner as many countries get closer every year.

This will be a state of Quantum Advantage. Also known as quantum supremacy, it sounds much bigger than it is: the point at which a quantum computer can solve a specific problem that is infeasible for a classical computer to solve and the algorithm used. In recent years multi-qubit processors of several dozen to 50 qubits have been built. Intel is distributing its 12 qubit quantum processor the Tunnel Falls chip  to a few academic research labs and its quantum SDK (software development kit) to sprout a community.

What else is needed?

While significant progress has been made in the development of the quantum internet, further advancements and refinements of essential hardware components are necessary to fully unlock its vast potential. Scientists and researchers are diligently working on perfecting the generation, transmission, and synchronization of qubits, which serve as the backbone of this revolutionary network.

They are addressing technical challenges to create a strong, scalable, and efficient quantum internet infrastructure. Their goal is to connect quantum computers over long distances, revolutionizing communication, cryptography, computing, and scientific discovery. The convergence of these technologies is remarkable.

A Glimpse into the Future of the Quantum Internet

The concept of a quantum internet represents a significant leap forward in the field of communication. It aims to establish a network capable of transmitting quantum information between distant computers and devices, enabling the realization of applications that were previously unimaginable to theoretical physicists.

Harnessing the principles of quantum mechanics, this groundbreaking network promises to enable secure and ultra-fast communication, however work must be done to scale it up and to reduce errors. Promising research includes:

- Ion Trap, transmons, and Nitrogen-Vacancy centers are considered some of the most promising systems for practical quantum computing.

- Basic requirements for universal quantum computing (QC) have been demonstrated with ions, and quantum algorithms using few-ion-qubit systems have been implemented.

- Efforts are being made to increase the scale of trapped ion quantum computers while mitigating decoherence and control errors.

In addition to its applications in cryptography and computing, the quantum internet also revolutionizes scientific research. By enabling the seamless sharing of quantum information, researchers can collaborate and analyze data across various fields such as quantum chemistry, material science, and fundamental physics. The quantum internet empowers scientists to explore new frontiers and make groundbreaking discoveries that were previously hindered by geographical limitations.

A global quantum internet is probably closer than we think. 

As researchers continue to solve the problems of making a quantum internet, we can anticipate a future where the quantum internet plays an inevitable role in transforming industries and reshaping the way we communicate, compute, and study the mysteries of the universe.

Much of this research is if from the United States Department of Energy and published in: Physical Review Letters

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