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Quantum-encrypted communication and quantum computing promise to be safer and more secure ways of communicating, but a variety of challenges are keeping these goals from being achieved.

But new research has taken us an inch closer to the goal.

Quantum communication involves the sharing of quantum information over long distances. But in order to crack this, first the concept of quantum memory needs to be addressed.

Quantum memory means an interaction between light and matter that allows quantum information, stored in light, to be retrieved in a similar way to the memory in a classical computer.

Previous attempts at building a quantum memory storage system have been too big to be of use at the scale needed, the size of a computer chip.

Now researchers in China and the US have come up with quantum storage box, small enough to be used on a chip. The device is a nano-sized cavity, around one thousandth of a millimetre, filled with the element neodymium inside a crystal structure. The paper is published in the journal Science.

The photons are stored in an ensemble of rare-earth neodymium atoms, says Andrei Faraon, from the California Institute of Technology, and co-author on the paper.

Inside, the atoms are trapped in a crystal called yttrium orthovanadate (YVO4). The ensemble is small, and by itself would not be able to absorb the photons, says Faraon. This is why we make an optical cavity, or resonator, in the YVO crystal, that enhances the interaction between the atoms and the light, so the absorption of photons by the atoms becomes efficient.

Dr. Tian Zhong

To store the photons, the cavity is prepared in a special way using a sequence of laser pulses. This preparation means that after the photons are absorbed they are automatically re-emitted after a certain short amount of time, or 75 nanoseconds to be precise. To implement a quantum memory using this device, we store photons that are shaped as two pulses, early and late pulse, says Faraon.

Quantum mechanically the photon exist in a superposition of early and late. This means they exist as a combination of the two phases at the same time. After the pulses are retrieved, it closely resembles the stored pulses, meaning the memory works.

Faraon hopes this new device, which is much smaller than anything made previously, will help us to crack quantum communication. In the future it could be used to transfer information at the quantum level at long distances via optical fibres, Faraon says. A quantum memory is essential in most schemes to transfer quantum information at long distances.

Quantum-encrypted communication would be much more secure than the mathematical algorithms used currently. This is because of the properties of quantum mechanics called Heisenbergs uncertainty principle.

Currently, information can be encrypted with techniques based on mathematical algorithms. It is difficult to figure out the exact algorithm used to encrypt a piece of data, making the approach largely safe for now.

However, experts anticipate computers powerful enough to crack the codes will surface in the next 10 to 20 years. This development would mean current encryption methods would be redundant as they could easily be broken.

Last year, researchers at Chatham House's International Security Department said satellites and other space communications technology are at significant risk from hackers and cyber attacks.

But there is a potential solution and this is where quantum mechanics comes into it. Heisenbergs uncertainty principle means the act of observing a particle creates certain changes in its behaviour.

Specifically, it means we cannot know both the momentum and position of a particle to the same degree of certainty at once. Quantum encryption uses this to create encoded data in the form of light that, if intercepted, will change its behaviour. This can alert the people communicating that the security key is not safe to use.

Continued here:
Quantum encrypted box hints at unhackable communication - Wired.co.uk