Crypto Quantum Leap
Better Quantum Codes May Be Indicated by New Entanglement Results
They demonstrated that even when two entangled quantum particles are separated by enormous distances, they must be seen as a single system since their states are inextricably linked.
This "nonlocality" phenomenon actually means that something that is thousands of kilometers away can instantly affect the system you are currently looking at.
Computer scientists can create uncrackable codes thanks to entanglement and nonlocality.
A pair of particles are entangled and then distributed to two people using a method called device-independent quantum key distribution.
Now that the shared characteristics of the particles may act as a code, communications will remain secure even from quantum computers, which are capable of defeating traditional encryption methods.
However, why stop at only two particles? The number of particles that can simultaneously be in an entangled state has no upper bound in theory.
A fully distributed quantum-protected internet has long been a goal of theoretical physicists, who have long imagined three-way, four-way, and even 100-way quantum links.
Recently, a lab in China appears to have created nonlocal entanglement between three particles simultaneously, which could strengthen quantum cryptography and expand the potential of quantum networks in general.
According to Peter Bierhorst, a quantum information theorist at the University of New Orleans, "Two-party nonlocality is weird enough as it is." However, it turns out that when there are three parties involved, quantum mechanics is capable of things that even go beyond that.
More than two particles have been entangled before by physicists. Depending on who you ask, the record is between 14 and 15 trillion particles.
However, these were simply a few centimeters or perhaps closer apart. Scientists must prove nonlocality in addition to multiparty entanglement, which is "a tough hurdle to achieve," according to Elie Wolfe, a quantum theorist at the Perimeter Institute for Theoretical Physics in Waterloo, Canada.
Once the particles are sufficiently separated that nothing else could be responsible for the effects, the question of whether the properties of one particle coincide with the properties of the other — the hallmark of entanglement — must be answered.
A particle that is still physically near its entangled twin, for instance, may generate radiation that affects the other particle.
However, if they are a mile away and measured almost instantly, they are probably just connected by entanglement.
The experimenters exclude all other explanations for the related properties of the particles using a set of equations known as Bell inequalities.
Similar steps are taken to establish nonlocality with three particles, but there are more scenarios to rule out.
This increases the difficulty of the measurements and mathematical hurdles that the researchers must clear to demonstrate the nonlocal relationship between the three particles.
You need to think of a unique strategy, according to Bierhorst and have the technology to set the ideal conditions in the lab.
In August, findings from a team in Hefei, China, represented a significant advancement. First, they entangled three photons and spread them out over a vast distance within the research center by firing lasers through a particular kind of crystal.
Then they measured a random characteristic of every photon at the same time. After examining the observations, the researchers concluded that three-way quantum nonlocality provided the most comprehensive explanation of the link between the three particles. It represented the most thorough proof of three-way nonlocality to date.
Technically, there is still little possibility that the outcomes were produced by anything else. One of the study's key authors, Xuemei Gu, acknowledged that there are still some unresolved issues.
However, by separating the particles, scientists were able to discount the most obvious competing theory for their observations: physical proximity.
The authors also used a more stringent definition of three-way nonlocality, which has gained popularity in recent years, as the foundation for their experiment.
Gu's three devices were unable to communicate, in contrast to earlier experiments where the devices that measured the photons could work together.
Renato Renner, a quantum physicist at the Swiss Federal Institute of Technology Zurich, explained that this restriction might be helpful in cryptography settings where any communication could be compromised. (In 2014, a Canadian team proved three-way nonlocality at a distance using the previous paradigm.)
Researchers using the new definition can now concentrate on extending the distance since they have successfully linked particles that are this far away.
Saikat Guha, a quantum information theorist at the University of Arizona, said that the experiment was a significant first step toward conducting farther-reaching, larger-scale studies.
According to Renner, this technology can immediately support more extensive quantum key distribution. The same Bell inequalities that physicists use to check for nonlocality may guarantee that your secret is totally secure if you employ entangled particles as the key to the encryption.
Then, even if your deadliest enemy deliberately manipulates the device you use to send or receive a message, they won't be able to determine your quantum key. Those are your personal secrets, shared only with the owner of the other entangled particle.
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