This exciting breakthrough today is clearly good news, as it should make quantum cryptography even more attractive.
"The researchers say that the relatively simple technology needed for such encryption could be incorporated into conventional communications satellites."
"Such cryptographic systems are already produced commercially, but they use fibre-optic cables. Losses in the cables limit the distance over which quantum keys can be sent to about 100 km, and that distance cannot be increased using repeaters, as is the case with classical data, because it is impossible to carry out the necessary amplification. Alternatively, quantum bits, or qubits, can be transmitted through the atmosphere, but this approach has a similar distance limit imposed by the curvature of the Earth."
I wonder if this was part of the infrastructure development that TGL was referring to last week? -
23/06/2015 08:30 UKREG Touchstone Gold Limited CQCL investment "... The Directors believe that QKE products will become essential for sensitive communications as soon as the requisite infrastructure is developed. ..." http://uk.advfn.com/news/UKREG/2015/article/67406777
In this latest research, the Italian group has gone one better, showing that it is possible to preserve the polarization state of those photons. Doing so is essential to quantum cryptography because it is the property of polarization – the orientation of a wave's oscillation – that is used to define the value of the qubits that make up a quantum key.
The researchers prepared the observatory's laser photons in one of four polarization states – horizontal, vertical, left-circular or right-circular – and beamed each of the states in 10-second bursts towards five satellites in orbits up to 2000 km above the Earth's surface. Their aim was to establish whether or not they could limit the fraction of qubits in each burst that had the wrong polarization after reflection to less than 11%. Above this figure, information theory dictates that no secret key can be established.
Villoresi and colleagues found, as hoped, that the error rates from four of the satellites were in single-figure percentages. These satellites employ corner-cube retroreflectors with metallic coatings, which are needed to preserve polarization states. The fifth satellite has uncoated retroreflectors and generated error rates of about 40%.
"Our results prove that quantum-key distribution from an orbiting terminal and a base station is not only a promising idea but nowadays is realizable," the researchers write.
Rotation on the fly
The tests did not involve the satellites transmitting qubits that could be used to make actual quantum keys, since the polarizations of the qubits were determined on the ground. But the researchers say that a straightforward modification of existing retroreflectors could make quantum-key generation a reality. All that is needed, they say, is to add a device known as a Faraday rotator and a random-number generator to each retroreflector in order to rotate the polarization of incoming photons on the fly.
Scientists in China have already developed a satellite that will generate quantum keys, and plan to launch it next year. This mission will create entangled pairs of photons in space and then send the two halves of each pair simultaneously to two communicating parties on the ground. The retroreflector-based scheme, on the other hand, involves transmitting the key to each user separately. According to Villoresi, the latter approach will be much cheaper and easier to implement and, he says, could "piggyback" on satellites due to be launched anyway.
The research will be described in Physical Review Letters and a preprint of the paper is available on arXiv.
About the author Edwin Cartlidge is a science writer based in Rome"
Exchanging messages with almost complete security by exploiting the strange laws of quantum mechanics should in future be possible on a global scale. That is the conclusion of physicists in Italy, who have found that the delicate states needed for quantum cryptography can be transmitted via laser beam from an orbiting satellite to a receiver on the surface of the Earth. The researchers say that the relatively simple technology needed for such encryption could be incorporated into conventional communications satellites.
Quantum cryptography involves two parties sharing a secret key that is created using the states of quantum particles such as photons. The communicating parties can then exchange messages by conventional means, in principle with complete security, by encrypting them using the secret key. Any eavesdropper trying to intercept the key automatically reveals their presence by destroying the quantum states.
Losses and curvature
Such cryptographic systems are already produced commercially, but they use fibre-optic cables. Losses in the cables limit the distance over which quantum keys can be sent to about 100 km, and that distance cannot be increased using repeaters, as is the case with classical data, because it is impossible to carry out the necessary amplification. Alternatively, quantum bits, or qubits, can be transmitted through the atmosphere, but this approach has a similar distance limit imposed by the curvature of the Earth.
This is where satellites could help. A single satellite, for example, could be used to send quantum data to two people on the Earth's surface to enable those people to share a secret key. To date, however, no device capable of generating or detecting quantum states – such as single photons – has been placed in orbit.
Paolo Villoresi of the University of Padua and colleagues have taken a creative approach to this problem by using the Matera Laser Ranging Observatory in southern Italy. This facility usually directs laser pulses at passing satellites and then measures the reflected pulses in order to measure tiny variations in the Earth's gravitational field. In 2008 Villoresi's team worked with a group of physicists at the University of Vienna to bounce very weak laser pulses from a satellite and then show that less than one photon per pulse could be detected on the ground (see "Single photons make the trek from space").
Just five US tech companies are sitting on over 400 billion dollars.
And what's more, there's an imperative for them to spend that money on non-US acquisitions, to avoid repatriating the money.
"These 5 tech companies are sitting on $430 billion in cash
By Charles Riley @CRrileyCNN
American tech companies are sitting on a massive pile of cash. Just five U.S.-based tech firms -- Apple, Microsoft, Google, Cisco Systems and Oracle -- had cash reserves of $430.3 billion at the end of 2014, the vast majority of which were held overseas, according to a new report from Moody's Investors Service.
Over the past five years, the tech sector at large accounted for 56% of the total increase in corporate cash. Apple, with at least $178 billion to its name, holds more greenbacks than many entire industries. It's a trend that is likely to accelerate. "Despite stronger returns of capital to shareholders, we expect the concentration of cash in the technology sector to grind higher over the next year," Moody's analysts wrote in the report. That's because most of the money is held overseas. Instead of bringing it back to the U.S., many firms choose to keep cash earned abroad beyond the reach of Uncle Sam, and his 35% tax rate on repatriated cash.
Roughly 90% of the total cash held by Apple, Microsoft, Cisco and Oracle is overseas. Google, meanwhile, keeps 60% of its $64 billion in cash abroad. As long as the companies don't bring that money home and reinvest it, they don't have to pay U.S. tax on it. The issue has long flummoxed policymakers in Washington, many of whom are inclined to offer the companies a one-time tax break in an effort to entice them to bring the money home. For now, Moody's said progress on the issue is unlikely. "At this stage in the political cycle and given strong differences on both sides of the aisle in Washington, we do not expect tax reform that would prompt overseas cash repatriation," the analysts wrote.
Here's a breakdown of the $430 billion in cash: Apple (AAPL, Tech30): $178 billion - 89% overseas Microsoft (MSFT, Tech30): $90.2 billion - 91% overseas Google (GOOG): $64.4 billion - 60% overseas Cisco (CSCO, Tech30): $53 billion - 94% overseas Oracle (ORCL, Tech30): $44.7 billion - 90% overseas
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