Category: quantum cryptography

China Just Used a Quantum Satellite to Send Data from Space to Earth

Quantum Leap For Communication

In a huge first for China and the world of quantum communication, researchers at the Quantum Experiments at Space Scale (QUESS) project have used a quantum satellite and quantum cryptography to transmit data to Earth from space. This data is potentially unhackable, thanks to quantum key distribution (QKD) technology. This was the first such transmission from the satellite, which was launched in August of 2016.

Today, encryptions are based on traditional mathematics. For now, they are mostly safe from hacking, but quantum computing would be able to completely change encryption as we know it now. Therefore, China is hoping to use transform encryption using quantum cryptography, and QKD technology in particular. QKD uses photons to transmit data, allowing two users in different places to, together, produce a common string of random bits called a secret key.

Image Credit: Chinese QUESS Research Team
Image Credit: Chinese QUESS Research Team

This kind of encryption is unhackable because there is no way to copy a photon in a precise enough way for hacking purposes, and measuring a photon would disturb it, clueing in the users about the disruption.

An Unhackable Future

This technology could have huge implications in cybersecurity. Businesses would be safer online, and e-commerce would be free of problems caused by hacking and identity theft. The tech would also make it far more difficult for governments to spy on private communications — something that global leaders and agencies around the world have a vested interest in.

China’s breakthrough transmission traveled about 1,200 kilometers to Earth from space, making it up to 20 orders of magnitudes more efficient than an optical fiber of the same length would be. This transmission is also much further than the previously understood limits of several hundred kilometers. This advancement is part of China’s overall push to become a major presence in space by 2030, a plan that includes reaching Mars by 2020.

China envisions a future with ground-based QKD networks and a global satellite system interacting to form a powerful, worldwide secure network. This transmission is the first step toward making this vision a reality.

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Physicists Take One Large Step Towards Proving Quantum Entanglement

New Loophole-Free Bell Test

One of the most interesting (and confusing) phenomena in quantum physics is quantum entanglement. We observe this quantum effect when we see entangled particles affect each other regardless of distance. For example, when we measure the state of one particle at a distance from another and the measurement of the state of the first instantly influences the state of the other, we have quantum entanglement.

Einstein was disturbed by this, and didn’t like the idea that quantum entanglement might violate the speed of light if the particles were somehow sending each other information faster than light could travel. Therefore, he developed the idea of local realism, which assumes a pre-existing value for any possible measurement of a particle — an objective value a particle must have. This theory is based on the idea of locality, the principle that there is a minimum amount of time it takes for distant objects to influence each other, and realism, the idea that objects exist whether or not they are measured.

In the 1960s, Physicist John Bell developed a famous test to determine whether particles really do influence each other in the way quantum entanglement suggests. In the Bell test, a pair of entangled particles are sent in different directions toward different locations. A device measures the state of each particle in each location, and the settings of each device are set at random; this way it’s impossible for device one to know the setting of device two at the time of measurement, and vice versa.

If quantum entanglement is real, then local realism shouldn’t work, and the Bell inequality test should be violated. If scientists do observe violations of the Bell inequality test, it means that quantum mechanics violates locality, realism, or both — making local realism incorrect. In recent research, physicists have reported some of the best evidence to date that quantum entanglement exists, and the quantum world is free of the constraints of local realism. Researchers performed a Bell inequality test that was, essentially, loophole-free, and demonstrated that two atoms one-quarter of a mile apart shared correlations probably caused by quantum entanglement. According to local realism, this should be impossible.

Image Credit: Rosenfeld et al. Published by the American Physical Society
Image Credit: Rosenfeld et al. Published by the American Physical Society
The only way the observed correlations could be explained by local realism would be if there were unknown “hidden variables” instead of quantum entanglement. And, according to the researchers, the odds of this being the case are less than one in a billion. The odds drop even further once all seven months of their accumulated data is accounted for, dipping to about one in ten quadrillions. The team concluded that the laws of the quantum world violate locality, realism, or possibly both.

Closing Loopholes

Although the test in this research was essentially loophole-free, all loopholes are not completely closed. One of the last possible loopholes that remain for most Bell tests has to do with how particle states are measured. It is critical that hidden variables are not somehow allowing particles to synchronize their properties by influencing the choice of measurement. This is called the freedom of choice or free-will loophole. In this research, the team used a high-speed quantum random number generator to eliminate this loophole, but the minuscule possibility of communication between random number generators or with other experimental elements technically remains possible.

Other research has used humans to randomly choose numbers, relying upon the randomness of unique human minds. The physicists in this study felt that an extraterrestrial random number generator is the only way to truly close the loophole since such massive distances would prevent covert communication. There are several such extraterrestrial random number generators under development in physics labs now, intended for this purpose.

Closing the loopholes matters, because scientists hope to use quantum entanglement to safely encode messages. The demands of quantum cryptography would mandate further refinement of the measurement process. Ultimately, the hope is that quantum entanglement will allow us to transmit quantum information over long distances almost instantaneously, making quantum computing and interstellar communication possible.

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China’s New Quantum Communication Network Will Be “Unhackable”

Securing the Internet

For a country notorious for its restrictive internet policies, China seems to be taking the lead on developing next-generation internet communications. The city of Jinan is set to become the hub of this quantum communications network that will boost Beijing-Shanghai internet when the project is launched by the end of August. It is set to become the world’s first “unhackable” internet communications network.

Unlike encryption methods that hide the key under difficult mathematical problems, quantum communication and cryptography use entanglement to do the trick. Concretely, the key is embedded in photons (light particles) and sent ahead of the encrypted message — a method called quantum key distribution (QKD).

Communication becomes “unhackable” this way because any attempt to intercept the key would be obvious to the sender and the intended recipient. What’s even more impressive is that China has the technology to extend quantum communications up to 400 kilometers (about 250 miles), as previously demonstrated in a quantum cryptography research in Hefei.

Favoring Entangled Particles Over Numbers

As technology becomes increasingly more complex, computers are becoming increasingly more powerful. This puts current encryption methods in danger, as number-crunching becomes easier with powerful computing power. Number-based keys need to be prolonged and constantly updated to keep up. QKD potentially solves all of this.

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Yet, for the most part, it seems China is leaving the West behind in pursuit of this technology. “For a long time people simply didn’t think it was needed,” Myungshik Kim from Imperial College, London, told the BBC. “The mathematical difficulty of the current coding system was so high that it was not thought necessary to implement the new technology.”

Recent security breeches and hacks, of course, reveal the error of this thinking. That’s one reason why China is pursuing quantum communication, but the tech has a number of other possible applications as well.

“We plan to use the [Jinan] network for national [defense], finance, and other fields, and hope to spread it out as a pilot that if successful, can be used across China and the whole world,” Zhou Fei, Jinan Institute of Quantum Technology assistant director, previously told the Financial Times.

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Physicists Develop Method to Send Secure Messages Using Quantum Memory

A Quantum Future

In a rather remarkable demonstration, physicists from the University of Science and Technology of China and the Nanjing University of Posts and Telecommunications have developed a way to use quantum memory for quantum secure direct communication (QSDC). They published the results of their experiment in the journal Physical Review Letters.

Whenever one encounters the word quantum, it’s not uncommon to feel a bit unsure of what it means. Since quantum refers to the smallest types of matter — usually particles — the concept shouldn’t be too fundamentally difficult to explain. Quantum physics, in essence, deals with “the physics of the small.”  Other theories or applications describe some behavior of particles. Quantum communication, the exchange of information using quantum particles, is one such application.

QSDC is a secure form of quantum communication; what’s commonly known as quantum cryptography.

“Quantum communication provides an absolute security advantage, and it has been widely developed over the past 30 years.” the researchers wrote in the study’s abstract, adding that “[QSDC] promotes high security and instantaneousness in communication through directly transmitting messages over a quantum channel.” Usually, QSDC protocols rely on fiber delay lines to transmit information, which have their limitations. The use of quantum memory, however, may be able to break through those limitations.

Long Distance Quantum Communication

As quantum communication is more secure, physicists have been working on ways to extend its usual reach. This requires quantum memory, which would allow it to effectively control information transfer in the quantum networks of the future. One method for quantum memory relies on using entangled photons. Entanglement is a quantum state that allows for particles to be linked even when separated by huge distances. In the case of quantum memory, the particles would be stored to establish entanglement between separated memories.

Researchers have demonstrated the necessary steps in a QSDC protocol: generating entanglement, having a secure channel, and the ability to distribute, store, and encode the entangled photons. To bypass the usual difficulty in decoding entangled photons, the researchers opted for an alternative method that was easier to implement.

While they were able to demonstrate QSDC effectively using quantum memory, the researchers hope to extend its distance further: perhaps up to 100 km (62 miles) if not more. Quantum teleportation and entanglement have already been shown to be capable of bridging such distances. This would be an important step to realize the future of long-distance, satellite-based and global-scale QSDC for a more secure transfer of information around the world.

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