As we move further into the digital age, securing your online accounts has never been more critical. One of the most effective ways to protect your accounts from unauthorized access is by using Two-Factor Authentication (2FA). This extra layer of security adds a second step to your usual login process, making it harder for hackers to gain access to your sensitive data. In 2025, setting up 2FA is…

Apple in December introduced three advanced security features focused on protecting against threats to user data in the cloud, representing the next step in its ongoing effort to provide users with even stronger ways to protect their data. With iMessage Contact Key Verification, users can verify they are communicating only with whom they intend. With Security Keys for Apple ID, users have the…

Physical security keys, a small external device that looks like a thumb drive or tag, provide extra protection for your Apple ID against phishing attacks. A security key is used for verification when signing in with your Apple ID using two-factor authentication and make your Apple ID more secure. Security Keys for Apple ID is an optional advanced security feature designed for people who want…

EFF lauds Apple for Advanced Data Protection end-to-end encryption for iCloud

The Electronic Frontier Foundation (EFF) is applauding Apple for its about-face on its misguided, ill-conceived plans to install photo-scanning software on its devices and for launching Advanced Data Protection which delivers end-to-end encryption to protect important iCloud data, including iCloud Backup, Photos, Notes, and more. Joen Mullin for EFF: We applaud Apple for listening to experts,…

Apple brings end-to-end encryption to iCloud Backup, Photos, Notes, and more

Apple today introduced three advanced security features focused on protecting against threats to user data in the cloud, representing the next step in its ongoing effort to provide users with even stronger ways to protect their data. With iMessage Contact Key Verification, users can verify they are communicating only with whom they intend. With Security Keys for Apple ID, users have the choice to…

“This is the realization of a goal that has been pursued by our quantum science and engineering community for more than two decades.” — Mikhail Lukin

Entanglement — what Einstein called “spooky action at a distance” — allows bits of information to be perfectly correlated across any distance. Because quantum systems can’t be observed without changing, Alice could use entanglement to message Bob without any fear of eavesdroppers. 

This notion is the foundation for applications such quantum cryptography — security that is guaranteed by the laws of quantum physics.

Quantum communication over long distances, however, is also affected by conventional photon losses, which is one of the major obstacles for realizing large-scale quantum internet. But the same physical principle that makes quantum communication ultra-secure also makes it impossible to use existing, classical repeaters to fix information loss.

How can you amplify and correct a signal if you can’t read it? 

The solution to this seemingly impossible task involves a so-called quantum repeater. Unlike classical repeaters, which amplify a signal through an existing network, quantum repeaters create a network of entangled particles through which a message can be transmitted.

In essence, a quantum repeater is a small, special-purpose quantum computer. 

At each stage of such a network, quantum repeaters must be able to catch and process quantum bits of quantum information to correct errors and store them long enough for the rest of the network to be ready. Until now, that has been impossible for two reasons: 

First, single photons are very difficult to catch. 

Second, quantum information is notoriously fragile, making it very challenging to process and store for long periods of time.

Lukin’s lab, in collaboration with Marko Loncar, the Tiantsai Lin Professor of Electrical Engineering at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), Hongkun Park, Mark Hyman Jr. Professor of Chemistry at the Harvard Faculty of Arts and Sciences (FAS), and Dirk Englund, associate professor of electrical engineering and computer science at MIT, has been working to harness a system that can perform both of these tasks well — silicon-vacancy color centers in diamonds.

“We plan to create large networks of entangled quantum memories and explore the first applications of the quantum internet.” — Ralf Riedinger

These centers are tiny defects in a diamond’s atomic structure that can absorb and radiate light, giving rise to a diamond’s brilliant colors.

“Over the past several years, our labs have been working to understand and control individual silicon-vacancy color centers, particularly around how to use them as quantum memory devices for single photons,” said Mihir Bhaskar, a Graduate School of Arts and Sciences (GSAS) student in the Lukin group.

The researchers integrated an individual color-center into a nanofabricated diamond cavity, which confines the information-bearing photons and forces them to interact with the single color-center. They then placed the device in a dilution refrigerator, which reaches temperatures close to absolute zero, and sent individual photons through fiber optic cables into the refrigerator, where they were efficiently caught and trapped by the color-center.

The device can store the quantum information for milliseconds — long enough for information to be transported over thousands of kilometers. Electrodes embedded around the cavity were used to deliver control signals to process and preserve the information stored in the memory.

“This device combines the three most important elements of a quantum repeater — a long memory, the ability to efficiently catch information off photons, and a way to process it locally,” said Bart Machielse, a GSAS student in the Laboratory for Nanoscale Optics.  “Each of those challenges have been addressed separately but no one device has combined all three.” Harvard Quantum Initiative Co-Director Lukin on ‘quantum supremacy’ and Google’s announcement of its achievement

“Currently, we are working to extend this research by deploying our quantum memories in real, urban fiber-optic links,” said Ralf Riedinger, a postdoctoral candidate in the Lukin group. “We plan to create large networks of entangled quantum memories and explore the first applications of the quantum internet.

“This is the first system-level demonstration, combining major advances in nanofabrication, photonics and quantum control, that shows clear quantum advantage to communicating information using quantum repeater nodes. We look forward to starting to explore new, unique applications using these techniques,” said Lukin.

The research was co-authored by Bhaskar, Riedinger, Machielse, David Levonian, Christian Nguyen, Erik Knall, Park, Englund, Loncar, Denis Sukachev, and Lukin.

It was supported in part by the National Science Foundation, the Department of Defense, the Department of Energy, the Air Force Office of Scientific Research and Office of Naval Research.

Quantum-Encrypted Keys

With entanglement, an object can be put into a quantum superposition of multiple states—like Schrödinger’s cat, both alive and dead at once—and that superposition can be shared with another object. In theory, these objects will maintain that connection even when separated, so that measuring one reveals the state of the other, no matter how far away. 

This isn’t merely of interest to quantum physicists. A quantum internet would allow ultra-secure communication of sensitive messages. One technique is to encrypt a pair of digital keys, a technology known as quantum key distribution (QKD). If two people both have these keys, they can talk without fear of being snooped on, because an eavesdropper would change the state of the keys and be found out.

But QKD relies on measuring the state of the quantum-encrypted keys, and since that measurement can be affected by conditions in the sending and receiving devices, you need to know their exact physical conditions. That can be impractical, because even tiny physical fluctuations can throw off the measurements.

That’s why the oddities of quantum entanglement have been seized upon to form the basis of an even better approach. Entanglement is much harder to pull off but in the long run could provide a more useful quantum internet than quantum keys. By entangling nodes on a network, you set up a connection between the entangled particles that bypasses the devices themselves, avoiding the unrealistic requirement that you know their exact state.

At least in principle. In practice, entanglement also requires ideal conditions. Quantum systems are sensitive to the tiniest disturbances: a change in temperature or a slight movement can throw everything off. A groundbreaking experiment in 2015 showed that quantum entanglement worked across a distance of just less than a mile (1.3 kilometers). In the years since, researchers have separated entangled particles by sending them down optical fibers and even up to a satellite and back. But the reliability has been very low.

In a paper in Nature today, Pan Jian-Wei at the University of Science and Technology of China, in Hefei, and his colleagues describe an experiment in which they demonstrate entanglement through more than 30 miles of fiber coiled in a lab, with lower transmission errors than previous attempts. “This is a big improvement,” says Pan, who is sometimes called the “father of quantum.” The trick was to find efficient ways to entangle two particles. The team used an atom, which stayed put, and a photon, which was sent down the fiber. They found that they were able to create an entangled pair of nodes much more reliably than was demonstrated in previous experiments—including the one setting the mile benchmark, which it beat by five orders of magnitude. 

How big a deal is this result? 

“It’s nice, but not nearly as big as it sounds,” says Stephanie Wehner, a researcher at QuTech, a quantum computing and quantum internet research centre in Delft in the Netherlands. Pan’s team used 30 miles of coiled fiber, which still demands an impressive degree of control over the whole system, but demonstrating entanglement between two nodes in one location is much easier than when they are actually 30 miles apart. 

But distance is one thing. Pan’s team also claims that its set-up is more reliable than previous examples and thus lays better groundwork for an actual quantum internet. Having demonstrated the techniques with a coiled fiber, he thinks they can readily extend them to work in a straight line. The methods developed in this work could be used to build quantum networks between cities in the near future, he says.

Unhackable Communication Protocols

Photon entanglement, in itself, is not new. In fact, the technology is already used for secure communication over thousands of kilometres, for example for satellite-to-ground or satellite-to-satellite communications. Until now, however, photons were generated in a specific wavelength – between 700 and 1,550 nanometres – which means that the light produced is close to the brightness of the sun.

Sunlight peaks around 500 nanometres, explains Matteo Clerici, senior lecturer at the University of Glasgow, who led the research; as a result, during the daytime, photon detectors struggle to differentiate the photons generated as part of a given experiment from the sun's light.

A team of researchers has published details of a new way to reliably create particles that are well-suited to use in quantum communications, which could lead to the un-hackable communication protocols that have long been pitched as one of the most useful applications of the technology. 

The scientists generated entangled photons, a method that applies one of the most intriguing properties of quantum physics. Entanglement is a phenomenon that occurs when two quantum particles become inextricably linked, which means that the way one behaves immediately affects the other, regardless of the distance between them. 

As a simple explainer, says Adetunmise Dada, research associate at the University of Glasgow, who participated in the research, imagine that you are measuring your entangled particles in bits. If one entangled particle reads as "1", then the other will be "1" too. If you get "0", so will the other one read "0". Now make it a string of particles: when you measure them, you generate a string of bits on one end, that is exactly the same as the string of bits on the other side.

Combine such a property with particles that travel at the speed of light, like photons, and you have a method to share information between two bodies, even if they are far apart, in a way that relies on the mechanical behavior of particles, rather than traditional cryptographic keys – and is therefore much less likely to be cracked by malicious hackers.

"If you have a single entangled photon, combined with hundreds of photons coming from the sun at a really close wavelength, coming towards a detector, you cannot distinguish between them," explains Clerici. Needless to say, the mixup can pose some problems for satellite communication.

Of course, you could start generating photons at wavelengths as far removed from the brightness of the sun as you possibly can, but then other challenges come into play. In some wavelengths, for example, which may be less bright, photons can instead be absorbed by certain types of atmospheric gases.

What the research team at the University of Glasgow managed to do, was to find a "transparency window" in the atmosphere, where there aren't many absorbing gases, nor is the sunlight overwhelming. That window is further into the infrared spectrum, at two micrometres wavelength.

Generating photons at two micrometres had never been demonstrated before. A major challenge for the researchers was to get their hands on the appropriate technology to conduct their experiment. "You need detectors that are able to see single photons at two micrometres, and we had to develop the right technology for these measurements," says Clerici. "And on the other side, you also need a specific piece of technology to generate the photons."

In partnership with technology manufacturer Covesion and the National Institute of Communications and Technology (NICT) in Tokyo, Clerici and his team engineered a nonlinear crystal that was suitable for operating at two micrometers. Photons are generated when short pulses of light from a laser source pass through the crystal.

In theory, the entangled photons generated at the new wavelength should be able to travel as far as the photons generated through existing methods, and used for satellite communication. But the new experiment is still in its early stages, and Clerici said that the team hasn't yet identified how much information the new technology can communicate, or how quickly.

FAQ: What's a YubiKey? And Why Does Apple Compatibility Matter?