Single Photons Bounced Off Orbiting Satellite

KentuckyFC writes "If we're ever going to benefit from the perfect security of quantum communication, we're going to need ways of transmitting entangled photons around the globe and certainly further than the current record of 144km through the atmosphere. Anton Zeilinger at the University of Vienna and colleagues have taken an important step towards this by bouncing individual photons off the Ajisai geodetic satellite (essentially a space-based disco ball) which is orbiting at 1400km. The group says the experiment is an important proof of principle for satellite-based quantum communications."

Comments

Re:Other than supposed security improvements...

[kelpless]

no cloning principle are exactly right. You cannot read and then reemit a photon with the same polarization Hmm. I think you meant you cannot read and reemit with 100% fidelity. http://www.icfo.es/images/publications/J05-055.pdf, "Quantum Cloning", Valerio Scarani, Sofyan Iblisdir, and Nicolas Gisin. This is a late 2005 review and of eavesdropping techniques for QKD. Much of the terminology of quantum physics is unfamiliar to me but I think the paper states that Eve could theoretically get 5/6 of the bits through cloning and to keep this from happening, Alice and Bob have to assume an eavesdropper if more than 11% of the bits have errors. When dealing with single photons, read errors will happen. There is also work at the University of Tokyo, the Japan Science and Technology Agency, and the University of York (Sam Braunstein and Akira Furusawa) on telecloning (combined quantum teleportation and quantum cloning) that I have a reference to an experiment done two years ago where they cloned 58% of the photons successfully out of a theoretical 66%.

Others have created quantum crypto systems that take the possibility of cloning into account, http://w3.antd.nist.gov/pubs/Mink-SPIE-One-Time-Pad-6244_22.pdf

'basic' quantum cryptography that is taught can be hacked This is true but I think not for the reasons you believe. Basic quantum crypto provides confidentiality only. To keep from being hacked, you must provide authentication as well (Alice must be able to prove she is communicating with Bob and not Eve). I haven't heard of a way to do this without falling back onto more conventional cryptographic techniques such as RSA signatures - at least when doing quantum crypto over fiber. Maybe sending photons through the atmosphere means you can actually just see if somebody is acting as a man-in-the-middle.