Thursday, September 1, 2016

quantum satellite

China made a splash on the scientific front recently by launching a “quantum satellite,” a 600 kilogram laboratory of quantum optics experiments. China has propelled itself to the forefront of quantum communications, hack-proof schemes that rely on the no-cloning theorem of quantum mechanics to communicate over large distances. With the satellite, they hope to establish a quantum channel between Beijing and Vienna (China is collaborating with the Austrian Academy of Sciences), far extending the current record of around 300 kilometers. Entangled pairs of photons will be generated via nonlinear crystal onboard the satellite and then fired towards Beijing and Vienna, along with some classical information on how to interpret the measurements (the requirement it be classical, i.e. no faster than the speed of light, prevents quantum nonlocality from violating Einstein’s special theory of relativity). From there, the standard experiments will be performed: Bell (or CHSH) tests to prove quantum entanglement over the 1200 kilometer distance by looking at statistical correlations that imply the state of one photon in Beijing depends on the other measured in Vienna, teleportation of a quantum state, and quantum key distribution by which private keys for encryption are shared publicly between two parties. [Full disclosure: Le’Veon Bell’s Joint Measurement is the name of a fantasy football team managed by yours truly].

 The 600 kilogram satellite itself [Cai Yang/Xinhua via ZUMA Wire]

The trick behind quantum encryption is that it relies on the property that measurement inherently destroys a quantum state. If an eavesdropper were to intercept some communication it would be immediately obvious that they had done so. This is in contrast to current encryption methods that are based on the supposed difficulty of mathematical problems such as calculating the factors of large numbers into primes (RSA, the universal method by which internet transactions take place), elliptic curves and discrete logarithms, being some other popular examples. RSA, by the way, is vulnerable to Shor’s algorithm, which could run on a quantum computer in the future. China’s foray into quantum encryption seems mainly to stem from, ahem, successful United States cyberespionage efforts penetrating Chinese networks. Successfully opening quantum channels between cities would secure communications (though it would not aid in their own cyber subterfuge).

Other groups getting into this quantum satellite business are universities from Italy, Canada, and a Singapore/British collaboration. What about these United States, you ask? Well it seems the US government canned funding for optical quantum information processing in 2010, purportedly because its application to quantum computing was overhypedUS funding for quantum computing is quite high at $200 million per year, although it largely neglects the communications and cryptology (well, at least publicly) aspects of quantum information. However, now that quantum information science is making it to the level of White House briefings, that may be changing.

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