From The Editor | January 30, 2024

John Bell, Quantum, And Faster Communication

John Oncea

By John Oncea, Editor

Global communications network-iStock-1255527368

Scientists from Russia and China have achieved a significant quantum communication milestone by establishing a secure link over a distance of nearly 2,400 miles utilizing China's quantum satellite, Mozi. Highly secure due to its resistance to hacking, quantum communication holds potential applications in fields like finance, government, and defense.

We recently looked at couples that worked together in the lab, starting with the Lavoisiers and ending more than 200 years later with the Mosers. We neglected to mention John and May Ross-Bell, two physicists who met while working on accelerator physics at the Harwell Science and Innovation Campus.

Mary, who died just shy of 100 in 2022, and John were married in 1954 and the two collaborated throughout their lives. Mary eventually joined the European Organization for Nuclear Research’s (also known as CERN) Accelerator Search Division, moved on to the Intersecting Storage Rings Division, and later still the Proton Synchrotron Division where she worked on electron linear accelerators and radio frequency separators. Towards the end of the 1980s, Mary expanded to accelerator physics, working on beamstrahlung, the accelerator analog of bremsstrahlung.

John, for his part, also took a position with CERN in Geneva. Linda Hall Library writes, “He got paid for designing particle accelerators, as did his wife, Mary. But in his off time, (John) thought long and hard about quantum mechanics.”

I Dabble A Little Bit

In 1964, Bell wrote On the Einstein–Podolsky–Rosen paradox, a paper that led to the famous Bell’s theorem which “states through an experimentally testable inequality that the predictions of quantum mechanics for the Bell’s polarization states of two entangled particles cannot be reproduced by any statistical model of hidden variables that shares certain intuitive features,” writes Frontiers.

The theorem also asserts that if certain predictions of quantum theory are correct, then our world is non-local, meaning there are interactions between events that are too far apart in space and too close together in time for the events to be connected.

“Bell's Theorem is regarded as an important idea in modern physics, but it conflicts with other well-established principles of physics,” Space.com writes. “For example, Albert Einstein had shown years before Bell proposed his theorem that information cannot travel faster than the speed of light. Perplexed, Einstein famously described this entanglement phenomenon as ‘spooky action at a distance’” since the particles seemed to be communicating faster than the speed of light.

“To explain the bizarre implications of entanglement, Einstein, along with Boris Podolsky and Nathan Rosen (EPR), argued that ‘hidden variables’ should be added to quantum mechanics to explain entanglement, and to restore ‘locality’ and ‘causality’ to the behavior of the particles,” writes Cal Tech.

The concept of locality implies that objects are only affected by their immediate surroundings. Causality, on the other hand, suggests that an effect cannot take place before its cause and that any causal signaling cannot travel faster than the speed of light. Niels Bohr famously challenged the EPR argument, while Erwin Schrödinger and Wendell Furry, in response to EPR, independently proposed that entanglement disappears with wide-particle separation.

Are You With Me So Far?

“In the opinion of many, Bell’s theorem is the most important contribution to quantum mechanics (some say to physics as a whole) made in the entire 20th century, since it confirms the nature of the quantum world,” writes Linda Hall Library. “It has been said that we live in the age of a Second Quantum Revolution, one that was begun by Bell.

“Experiments to test Bell’s theorem have been performed thousands of times, and Bell’s theorem has been confirmed in every instance. All those ‘quantum’ things that you have heard about, such as quantum computing and quantum cryptography, are the direct results of the work of John Stewart Bell. He would surely have received a Nobel Prize, had he not died, unexpectedly, in 1990, at the age of 62. He deserves to be as widely known as Einstein. Perhaps, in a hundred years, he will be so.”

Long story short, “quantum entanglement has been experimentally verified through tests such as Bell’s Theorem experiments,” writes Brainly. “In these experiments, entangled particles were separated by large distances, and measurements on one particle instantaneously affected the state of the other particle, even though they were far apart.”

The connection between entangled particles, which exist regardless of distance, has perplexed scientists and defied our intuitive understanding of how information and causality operate. Nevertheless, it highlights the distinctive behavior of quantum mechanics and has potential applications in fields such as quantum computing and secure communication.

I Told You That Story To Tell You This Story

So, if John Bell and his theorem are responsible for all things quantum it is he we have to thank for the recent announcement that scientists from Russia and China successfully established a quantum communication link over a distance of nearly 2,400 miles.

Quantum communication is a type of communication that uses qubits. Qubits are capable of holding binary information just like traditional bits. However, qubits are extremely sensitive to external interference. This makes it very easy for a quantum computer to detect any interference or interception with the qubits.

The communication, which spanned between Moscow and Urumqi in China, was encrypted using secure keys transmitted by China’s quantum satellite, Mozi, writes The South China Morning Post. A communication channel this secure would be used “for applications where the highest level of security is essential, such as in transmitting sensitive information in fields like finance, government, and defense,” adds Interesting Engineering.

As part of an experiment, a secret key was exchanged to decrypt two coded messages. The keys were based on a quote from Chinese philosopher Mozi and an equation from Soviet physicist Lev Landau.

“Quantum communication provides a secure way to transfer information, making it resistant to eavesdropping by hackers,” Interesting Engineering writes. “The encrypted data is transferred as ones and zeros along with a quantum key, ensuring that unauthorized individuals cannot access the information.

“Quantum communications are — in theory, at least — the most secure possible form of data transmission, exploiting quantum mechanics to be unbreakable without detection,” Tom’s Hardware writes. “The main drawbacks are the limited adoption/evolution of quantum computing and fundamental range weaknesses in current qubit transmission technologies— reportedly about 1,000 kilometers due to photon loss over long-distance wiring.”

Mozi helps overcome this limitation by allowing for long-distance quantum transmission and has allowed China to establish a national quantum network spanning thousands of miles.

While quantum communications via satellite is an accomplishment it isn't likely to become a dominant form of communication in the foreseeable future. However, Tom’s Hardware notes, “The rapidly approaching future of quantum computing may still be full of surprises, though, so who knows?”

Many think the world’s militaries will make use of this technology once it is up and running, but Alexey Fedorov of Russia’s National University of Science and Technology and the Russian Quantum Center says, “Quantum communication networks could have many uses, but for now, quantum systems would ideally be suited to scientific research.”

Tom’s Hardware adds, “While the technology is developing, it still seems there will be some time before it’s used on a large scale for any real purpose. But Fedorov did speak of interest in quantum computing from the Russian finance sector and even alluded to the possibility of a quantum communication network between BRICS nations (Brazil, Russia, India, China, and South Africa) in the future.”