Engineers at Nasa’s Jet Propulsion Lab, the University of Calgary, and the National Institute of Standards and Technology in Boulder, Colorado Researchers have achieved quantum teleportation over the farthest distance yet outside of the lab, by sending the quantum state of a photon across 3.7 miles (8.2 Kms) in a metropolitan network. Quantum teleportation is an essential quantum operation by which we can transfer an unknown quantum state to a remote location with the help of quantum entanglement and classical communication.
The experiments were conducted using ‘dark’ cables under the city of Calgary in Canada, and mark a major step toward the ultimate goal of a quantum Internet as researchers finally begin tests in real-world contexts. This means the Quantum Internet could be run over currently installed fiber optic networks. “This bring us closer to a future Quantum Internet that can connect powerful quantum computers with a security ensured by the laws if quantum mechanics,” said Quantumrun, Marcel.li Grimau Puigibert (one of the key players in the Calgary experiment)
Longer distances have been achieved in the past, but only in lab settings. A team at the National Institute of Standards and Technology in the US reported last year that it had achieved quantum teleportation over a fibre optical network more than 100km in length, but the whole cable was coiled within a laboratory. Scientists have also teleported photons through the air over 100km, but the technology can only be used at night and in remote areas because too many of the particles are generated by other sources including natural light.Using a cable shields the photons from interference and is viewed by researchers as a more practical way of harnessing the technology.
Chinese team, led by Professor Pan Jianwei and Professor Zhang, have also been able achieve “full” quantum teleportation of photons over a optical fibre network 12.5km apart.Zhang at the University of Science and Technology of China, said the team’s work was only a small step towards the construction of a quantum network. Many technical hurdles, such as storage for the extremely fragile quantum data, remained and it was difficult to predict when a global quantum internet would be operational.
French physicist Frederic Grosshans while commenting on the two experiments in the scientific journal Nature Photonics said, “The two experiments clearly showed that teleportation across metropolitan distances was technologically feasible.”The Chinese and Canadian teams used different approaches to carry out their experiments. The Chinese team demonstrated a fuller version of the quantum network with higher reliability, but the Canadian approach was more efficient, according to Grosshans. The Chinese method “comes at the price of a low rate of two teleported photons per hour, which would strongly limit its practical applications if it could not be improved”, he said. The Canadian method “allows a faster teleportation rate of 17 photons per minute”, but their low accuracy during transmission “also limits its immediate practical applications.”
Teleportation/ Entanglement is exploited by parallel computing, quantum communication, cryptography technology and distributed computing . The distribution of quantum states over long distances is essential for future applications such as Regional, National or global scale quantum networks based on Quantum Key Distribution. Such quantum internet will be useful for distributed quantum computing, distributed cryptographic protocols and dramatically lowering communication complexity. Short-distance quantum teleportation will play a role in transporting quantum information inside quantum computers.
“No one yet realises what the quantum internet will enable us to do said Prof. Ronald Hanson,”For example, people have calculated that you can increase the baseline of telescopes by using quantum entanglement. So, two telescopes quite far apart could have better precision than each of them individually would have. You could envision using this quantum internet to create entanglement between atomic clocks with different positions in the world and this would increase the accuracy of timekeeping locally.’
Quantum teleportation is the idea that quantum states – and they contain information of course – disappear on one side and then reappear at the other side. What is interesting there is that, since the information does not travel on a physical carrier, it’s not encoded in a pulse of light, or in a letter, it does not travel between sender and receiver, it cannot be intercepted. The information disappears on one side and reappears on the other side.
‘Quantum teleportation is the most fundamental operation that can be done on the quantum internet. So, to get entanglement distributed over long distances you are actually teleporting the entanglement from one node to the other. ‘In a classical network you send your data package, and there is an address contained in that, and the router will read off that information and send it on to the next node. We don’t want to do that with these quantum signals. We want to send these quantum signals by teleportation so they don’t have to go through the (optical) fibre, they disappear in one side and reappear in the next.’
Nasa researchers explain transportation: “If a hypothetical particle called Photon 1 is entangled with Photon 2, the latter can be sent to a distant location, and they still will remain linked, t So, if in the second location Photon 2 meets a third particle, Photon 3, and interacts with it, the state which Photon 3 transfers to Photon 2 will automatically be teleported to its entangled twin as well, Photon 1. This is a ‘disembodied transfer,’ meaning that Photons 1 and 3 never interact. Harnessing this type of system could revolutionize encrypted messaging, allowing senders to transmit ‘disembodied’ information to the desired recipient that would be impossible for an eavesdropper to intercept.”
Quantum key distribution (QKD) uses quantum mechanics to guarantee secure communication. It enables two parties to produce a shared random secret key known only to them, which can then be used to encrypt and decrypt messages. QKD is said to be nearly impossible to hack, since any attempted eavesdropping would change the quantum states and thus could be quickly detected by data flow monitors. This technology offers extremely high security, but its application is currently restricted to metropolitan area networks.
Extending the Quantum network using Quantum repeaters
The direct approaches are limited to much less than 500 km, even under the most optimistic assumptions for technology evolution due to transmission losses. Extending the quantum network relies on two ways one is use of quantum satellite which can connect over large distances, China has already launched a quantum satellite. Another method is to use optical amplifiers as Robert Thew, who co-leads the Quantum Technologies Group at the University of Geneva explains, “In classical communication, amplifiers are used to regenerate the signal. However, in the quantum regime this adds too much noise and destroys the coherence of the quantum states” .
“In our experiments, we overcome this limitation by exploiting a teleportation-based approach, which can be thought of as a lossless channel.”The team, which includes researchers from the University of Geneva and Delft University of Technology, has demonstrated the heralded photon amplification technique over a simulated distance of 50 km, reporting its results in the journal Quantum Science and Technology.
As the researchers highlight, one of the major applications of heralded photon amplification is for so-called device-independent quantum key distribution – an approach aimed at certifying the security of a connection with minimal assumptions about the system itself and the technology that is exploited.
At the heart of the approach is the conceptually simple idea of sending a single photon on a 50/50 beam-splitter to generate entanglement. Repeating the process in succession and monitoring the output from single photon detectors provides the building blocks for studying quantum communication protocols. Taking this a step further, it’s possible to distribute the entanglement between two locations, generating a unique key for encrypting data transmission.
“The single photon, or path entangled, scheme we are using is also closely connected to quantum repeaters in terms of how entanglement is distributed in these long distance and fully-quantum network solutions,” commented Thew. “Our next step is to develop compact and more efficient heralded photon sources that can be more easily deployed, allowing us to push these sorts of experiments into real-world networks.”
A promising alternative for long distance quantum states distribution is the use of quantum repeaters. NTT/NIST has utilized teleportation technique could be used make quantum repeaters. Quantum Repeaters can be thought of as being analogous to the optical amplifiers that provide an economic and compact solution for long distance classical communication. However, whereas the idea of amplifiers is to regenerate the classical optical signal, what these Quantum Repeater links do is to create sections of lossless transmission line over which the quantum state is teleported. .” The key technology for implementing quantum repeaters is quantum memories that allow the storage of quantum states.
The researchers expect that the highly efficient multifold photon measurement using the SNSPDs will pave the way toward advanced quantum communication systems based on multiphoton quantum states such as the Greenberger–Horne–Zeilinger state and the cluster state over optical fiber.
Increasing the dimensionality of quantum entanglement is a key enabler for high-capacity quantum communications and key distribution, quantum computation and information processing, imaging and enhanced quantum phase measurement.
NIST Team’s Distance Record for Quantum Teleportation, step towards Unhackable Global Quantum Internet
Earlier, Researchers at the National Institute of Standards and Technology (NIST), “teleported” or transferred quantum information carried in light particles over 100 kilometers (km) of optical fiber, four times farther than the previous record.
The experiment confirmed that quantum communication is feasible over long distances in fiber based on photon entanglement distribution. Quantum key distribution (QKD) over optical fiber with schemes based on attenuated laser light have resulted in the exponential decrease in the key rate caused by fiber loss
Quantum teleportation over optical fiber has been challenging also because the low photon detection efficiencies of typical telecom-band single-photon detectors. In these experiments, however, the ultra sensitive photon sensors allowed for more precise detection. ‘The superconducting detector platform, which has been pioneered by JPL and NIST researchers, makes it possible to detect single photons at telecommunications wavelengths with nearly perfect efficiency and almost no noise,’ said Daniel Oblak, of the University of Calgary’s Instutite for Quantum Science and Technology. ‘This was simply not possible with earlier detector types, and so experiments such as our, using existing fiber-infrastructure, would have been close to impossible without JPL’s detectors.’
Moving forward, the researchers will build repeaters to teleport entangled photons across longer distances. With ‘super-sensitive photon detectors,’ they say repeaters could even send entangled photons across the country. And eventually, space-related communications could achieve teleportation without the use of repeaters, with photons instead fired into space with lasers, and the states teleported from Earth.
“By using advanced superconducting detectors, we can use individual photons to efficiently communicate both classical and quantum information from space to the ground,” Shaw said. “We are planning to use more advanced versions of these detectors for demonstrations of optical communication from deep space and of quantum teleportation from the International Space Station.”
Researchers Achieve Long-Distance Teleportation of Entanglement
Quantum entanglement could allow users to send data through a network and know immediately whether that data had made it to its destination without being intercepted or altered. This allows us to create a private key between two remote legitimate users, say the sender Alice and the receiver Bob, by transmitting the photons over a quantum channel, and performing a protocol, BB84 for example, to distill a final, shared secret key.
Zeilinger and his team has generated entanglement between independent qubits over a record distance of 143 kilometers, linking the Canary Islands of La Palma and Tenerife. For the teleportation of entanglement, they made use of phenomenon called Bell-state measurement, by which it is possible to entangle two photons by performing a joint measurement on them.
Assume you have two pairs of entangled photons, “0” and “1” in the receiving station and “2” and “3” in the transmitting station. Now, assume you send photon 3 from the transmitter to the receiver, and perform a Bell-state measurement simultaneously on photon 3 and on photon 1, due to which, photons 3 and 1 become entangled. But surprisingly, photon 2, which stayed home, is now also entangled with photon 0, at the receiver. The entanglement between the two pairs has been swapped, and a quantum communication channel has been established between photons 0 and 2, although they’ve never been formally introduced.
Entanglement swapping in conjunction with quantum memory will be an important component of future secure quantum links with satellites, says Thomas Scheidl, a member of Zealander’s research group.
China building Satellite based worldwide quantum Network.
Since the first experimental demonstrations using photonic qubits and continuous variables, the distance of photonic quantum teleportation over free-space channels has continued to increase and has reached >100 km. European physicists have been able to teleport photons between the two Canary Islands of La Palma and Tenerife off the Atlantic coast of North Africa, a distance of almost 150 kilometres. Next step was to teleport it to satellite.
China has launched the world’s first quantum communications satellite officially known as Quantum Experiments at Space Scale, or QUESS, satellite. The launch took place at 17:40 UTC Monday (16th Aug 2016) from the Jiuquan Satellite Launch Centre in the Gobi Desert, with a Long March 2D rocket sending the 620 kilogram (1,367 pound) satellite to a 600 kilometer (373 mile) orbit at an inclination of 97.79 degrees. “In its two-year mission, QUESS is designed to establish ‘hack-proof’ quantum communications by transmitting uncrackable keys from space to the ground,” Xinhua news agency said. said.
The satellite will enable secure communications between Beijing and Urumqi, Xinhua said. “The newly-launched satellite marks a transition in China’s role – from a follower in classic information technology development to one of the leaders guiding future achievements,” Pan Jianwei, the project’s chief scientist, told the agency. Quantum communications holds “enormous prospects” in the field of defense, it added.
China then plans to put additional satellites into orbit China hopes to complete a QKD system linking Asia and Europe by 2020, and have a worldwide quantum Network.
However realistic National and Global Quantum would likely be a hybrid one based on both free space and fiber optic links. The fiber network could complement free space network in urban settings where line of sight is blocked by buildings e.t.c.
High quantum efficiency High Temperature superconducting single photon detectors
Ultrafast, high quantum efficiency single photon detectors are essential for scalable quantum computers and quantum key distribution. Recently, superconducting nanowire single-photon detectors (SNSPDs) with >90% detection efficiency in the 1.5 μm band have been realized using superconducting nanowires made of amorphous tungsten silicide (WSi).
However the Researchers employed molybdenum silicide (MoSi), superconducting single photon detectors, to perform photonic quantum teleportation over fiber. The choice of MoSi instead of WSi allowed operation at a higher temperature with less jitter.
“Only about 1 percent of photons make it all the way through 100 km of fiber,” NIST’s Marty Stevens says. “We never could have done this experiment without these new detectors, which can measure this incredibly weak signal.”
Photon encoding based on time-bin qubit
Various quantum states can be used to carry information; the NTT/NIST experiment used quantum states that indicate when in a sequence of time slots a single photon arrives
As a quantum information carrier, they use a photon encoded as a time-bin qubit i.e. which of time slots a single photon arrives, instead of polarization qubit because it is generally difficult to preserve a polarization state in a long fiber.
NIST experiment added quantum information to a photon in its position in a very small slice of time of only 1 nanosecond, “early” or “late” in time bin. A special crystal splits one input photon to two entangled photons, a helper photon and an output photon. The “output photon” is sent over 102 km of optical fibre.
They then determined the state of entangled “helper photon” by bouncing it off a photon that they has been generated with a known state of “early” or “late”time bin. Pair of detectors through their timing difference are able to determine the state of helper photon. Once they’d worked out the state of the helper photon, they knew the state of the output photon as they are both entangled, and they use another pair of detectors on the other end to confirm this and that state has indeed been teleported over 102 kms.
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