Quantum of solace as breakthrough looms

[cirr]

2013-10-17 08:26

New communications technology would have 'unconditional security'

Matter transfer, like the astonishing technology in Star Trek, is possible in real life.

Simply speaking, all you need is to convert an object into an energy pattern, transmit the energy, then reconvert it into matter.

Though transferring a person is still far away, we are stepping closer to transferring elementary particles.

"We're in the last step, connecting distant cities with quantum networks via satellite," Pan Jianwei, a professor at the University of Science and Technology of China and a leading quantum expert, said in an exclusive interview.

Within five years, he and his team plan to build a quantum network covering a wide area.

"The biggest advantage of quantum communication, compared with the current means of communication, is its unconditional security," Pan said.

He has built a metropolitan area quantum network in Hefei, Anhui province, linking 46 nodes, including government agencies and financial institutions, allowing real-time voice communication, messages and file transfer.

"The application of quantum communication is wide, it can be used on any confidential information," said Chen Kai, a professor who works with quantum networks.

Unique nature

The reason that information is safer on quantum networks lies in the properties of photons, Pan said.

Computer networks utilize binary code (a series of zeros and ones) to convey information. The messages can be copied if they are captured during transmission.

But photons, the smallest unit of energy, have a unique nature in that they can exist in many possible states at the same time.

"In other words, the state of a quantum photon could be zero or one, or both zero and one at the same time," Pan said.

So on a quantum network the information can neither be captured nor copied because an eavesdropper cannot duplicate the state of a photon. If the photons are disturbed, observable changes will be detected and expose the listener.

"The information, encoded in the photons, is like being locked in a safe box. The thieves do not know the information in the box and can't copy it if they don't open the box. But if they try to open it they have to smash the box, which will leave a trace," Pan said.

As for current network transmissions, Pan said that, "you thought you put the information in a safe box, but it turns out that your box is made of glass, so everybody can see the information inside and copy it, without opening it and leaving traces".

In March, Pan and his team started a project to build a 2,000-km quantum network linking Beijing and Shanghai. The network, expected to be put into service in three years, will mainly be used to transfer confidential banking information.

Yet metropolitan and intercity networks were never the ultimate goal of Pan's group. Their aim was to teleport quantum information across the planet by beaming the signal to a satellite and bouncing it back.

Yet there is no point in developing a satellite quantum communication network if you have no one to talk with. So Pan invited his doctoral tutor and one-time rival Anton Zeilinger.

This year, the team sent photons to an orbiting satellite and detected thousands of the photons back on Earth.

In June, MIT Technology Review's arXiv Blog reported the experiment as a "small victory in this quantum space race" between China and Europe.

"What is abundantly clear is that the quantum space race is rapidly heating up. But the embarrassing truth for American science is that the US isn't yet a player in the quantum space race (at least not publicly). Perhaps that's something that should change," the author wrote.

In 2016, China plans to launch a satellite dedicated to quantum experiments, the Chinese Quantum Science Satellite, that would put it ahead of the US and Europe.

"The satellite will provide scientific answers to the feasibility of intercontinental quantum teleportation—to make it simple, whether I can talk to my friend in Vienna from Beijing on a quantum phone," Pan said.

A report in Nature magazine said that teleporting photons to a satellite would "establish the first links of a‘quantum Internet' that harnesses the powers of subatomic physics to create a super-secure global communication network. It will confirm China's ascent in the field, from a bit player, little more than a decade ago, to a global powerhouse".

Although the practical application of quantum networks that link every corner on Earth would need more than just one satellite, Pan is happy to see China being "one step ahead of world competitors".

"There is fierce international competition in quantum communication, especially from the US and Germany," Pan said.

"Quantum communication represents a significant direction of technological development, and the best thing we can do is to think big, think ahead and plan in advance."

Quantum of solace as breakthrough looms-Eastday

 

[cirr]

First quantum communication，followed by quantum computer and then quantum internet。

All planned and in the pipeline。

 

[cirr]

Quantum memory, another piece in the jigsaw of quantum computing...

USTC Unveils the First Quantum Memory that Records the Orbital Angular Momentum of a Single Photon

[2013-10-13]

The cold atomic physics research group of Key Laboratory of Quantum Information, CAS, led by academician GUO Guangcan, has achieved significant progress for high-dimensional quantum memory: the group leader, Prof. SHI Baosen and his collaborators realize the storage and release of a single photon with a spatial structure, carrying the orbital angular momentum (OAM) in a cold atomic ensemble for the first time. This progress clearly demonstrates the possibility for high-dimensional quantum memories and makes the first important step towards realizing a long-distance quantum communication with large information-carrying capability based on high-dimensional quantum repeaters. The main results have been published in Nature Communications online on Oct. 2nd.

Usually quantum information is encoded in a two-dimensional space spanned for example by orthogonal polarizations of a photon, a robust quantum information carrier. In this case, each photon could carry at most a bit information. If the photon could live in a high-dimensional space, for example, spanned by the inherently infinite-dimensional OAM, then the information carried by each photon could be increased significantly (improved from a bit to log2d bits). Moreover, in comparison to a two-dimensional state, high-dimensional states show many interesting properties: enable more efficient quantum-information processing, and afford a more secure flux of information in quantum key distribution, etc. Quantum repeaters are indispensable for increasing the transmission distance and improving the quantum information processing efficiency, among which a quantum memory is the key component consisting of the quantum repeater. If we could realize the reversible transfer of a high-dimensional quantum state between a true single photon and a matter used as a quantum memory with high fidelity and reliability, then we may have the potential solution in enhancing the channel capacity significantly in addition to overcoming distance limitations of quantum communication schemes through transmission losses, a high-dimensional quantum network may become practical. Therefore many groups and researchers are devoted to performing the storage of a light lived in a high-dimensional space. Although some works have reported on the storage of a light carrying OAM or a spatial structure in different physical systems, these works involve bright lights. So far there is no any work reporting on the storage of a photon encoded in a high-dimensional space in any physical system. Constructing such a quantum memory is a hot topic and big challenge.

SHI Baosen and his Ph. D candidates, DING Dongsheng and others are devoted to solving the above problem, and have achieved some progresses on the storage of a light carrying a spatial structure (see PRA, 87, 013835, 013845, 053830, (2013)). Recently, they make big progress along this research direction: report on the first experimental realization of a true single-photon-carrying OAM stored via electromagnetically induced transparency (EIT) in a cold atomic ensemble, demonstrating the possibility for building up high-dimensional quantum memories. In the experiment, they prepare two cold atomic clouds by laser cooling and trapping techniques in two magnetic-optical traps. One atomic cloud is used to as a nonlinear media to prepare a heralded single photon. Then this single photon, imprinted a special structure and carried OAM by a spiral phase plate, is stored through EIT in the second atomic cloud and retrieved after a programmed storage time. The experimental results clearly demonstrate that not only the single photon with OAM could be stored with high fidelity, but also with the help of a well-designed Sagnac interferometer and quantum tomography technique, the superposition state of OAMs carried by the single photon could be also well preserved during the storage.

Figure caption: A heralded single photon is generated through the spontaneous four-wave mixing in Mot 1 (a), then this single photon, imprinted a special structure and carried OAM by a spiral phase plate, is stored through electromagnetically induced transparency in Mot 2 (b). (c) is the image of the photon carrying. We experimentally measure the image carried by the photon before storage and after that along the transverse position, the results are shown in (d) and (e) respectively, exhibiting strong similarity. The solid lines are theoretical fits./ Image by SHI Baosen's Group.

Before published in a peer-reviewed journal, the main results are firstly public in the academic website of arXiv (arxiv:1305:2675), immediately attracts people’s attention: MIT TechnologyReview comments online: "First Quantum Memory That Records The Shape of a Single Photon Unveiled in China" and "The world’s first quantum memory that stores the shape and structure of single photons has been built in a Chinese lab". Subsequently, some other websites reprint these comments. Now, these results have been published online in journal Nature Communications with positive comments as "This is extremely impressive work, and establishes a very high standard in the rapidly growing field of quantum memories. In fact, the authors could have probably split the results into two papers. But taken together, this demonstration of the ability to generate, store, and read out on-demand, arbitrary OAM qubits encoded onto true single photons, represents an exciting watershed in the development of quantum-enabled technologies. The results will have a large impact within the quantum information and quantum atom optics communities, and should be of general interest to a wider physics audience. I am therefore very happy to recommend publication in Nature Communications. I look forward to the future results from this research group."...

This work is supported by the National Natural Science Foundation of China, the National Fundamental Research Program of China.

Contact: Prof.SHI Baosen, drshi@ustc.edu.cn

University of Science and Technology of China

 

[Destro]

Wonderful news.

 

[grandmaster]

why post such a important thing to public? should not let such important research to be published in any journal

 

[S10]

why post such a important thing to public? should not let such important research to be published in any journal

Just because I tell you how to build a car, does not mean you can build one. It's more of general knowledge than technical know-how.