Friday, June 16, 2017

Chinese send entangled photons

The LA Times reports:
Chinese scientists have just set a record in quantum physics.

For the first time, pairs of entangled photons have been beamed from a satellite in orbit to two receiving stations almost 1,500 miles away on on Earth.

At the same time, the researchers were able to deliberately separate the entangled photon pairs along a greater distance than has ever been recorded.

The experiment, described Thursday in the journal Science, represents the first measurable proof of an idea that has long been theorized but never tested, experts said.

“This is the first time you have a quantum channel between a satellite and the ground that you can actually use,”
No, this is not something useful.
Although the experiment was successful, the rate of sending and receiving entangled photons described in the paper was still quite low. Of nearly 6 million entangled photon pairs generated by Micius each second, only one pair was detected at stations here on Earth.

“The communication rates here are not yet sufficient for a practical application,” said Wenjamin Rosenfeld, a physicist at the Ludwig-Maximilians University in Munich.

However, he added that the mission represents a proof-of-principle demonstration of a quantum communication protocol that could be available in the near future.
So it sends one bit per second?!

The slowness is not the main problem. The security depends on accounting for all the photons. The system does not really stop eavesdropping, but alerts the parties if any photons are unaccounted for, as that might be a symptom of an attack.

But the Chinese can only account for one out of 6M photons anyway?!

Meanwhile, there are terabits of encrypted data being transmitted on satellites every second, and the method does not suffer the vulnerabilities of this quantum method.
That’s neat, but is this going to affect my life in anyway?

Not immediately, but eventually, it probably will.

For example, distributing entangled photons over large distances could be used to establish unhackable communications via what’s known as quantum cryptography.

This application relies on another strange aspect of quantum mechanics — namely that the simple act of observing a photon disturbs it and causes it to change its orientation.
So if an evesdropping observers a photon, he changes it, and might get exposed.

But no, this has no practical value. Who wants a system that can be sabotaged by someone observing a photon?
“One measurement alone doesn’t tell you they are entangled, you need to repeat it many times,” he said. “With entangled photons no matter what you measure, or how many times you measure, or which side of the pair you measure, you always get perfect correlation.”

How is this possible?

Another great question. This one is more difficult to answer.

Scientists have not been able to explain why entanglement occurs. All they know is that it exists.

Einstein referred to the phenomena of entanglement as “spooky action at a distance.” Others have said it is kind of like the physics version of voodoo.
The correlations are perfect is the equipment is perfectly aligned and a perfectly parallel measurement is done.

In practice, these things are not perfect, and some photons are lost. And you can't really detect one photon being stolen, you can only make a statistical conclusion if a lot of your data has been stolen.

On the other hand, the non-quantum cryptographic technologies work just fine.

I would think that if the LA Times asked expert opinion from physicists and cryptographers, at least half of them would know that this whole field is a scam. Why don't any of them tell the LA Times?

1 comment:

  1. Roger, why do you act puzzled? It seems simple to me:

    "Disappointing indeed, but the reality is rich countries have been dealing with this problem for decades. A staggering 96 per cent of America’s net job growth since 1990 has come from sectors known to have low productivity (construction, retail, bars, restaurants, and other low-paying services were responsible for 46 percentage points of total growth) and sectors where low productivity is merely suspected in the absence of competition and proper measurement techniques (healthcare, education, government, and finance explain the remaining 50 percentage points)"

    The anthill conspires and there are a lot of ants in China. Newspapers are just impression management.