Teleportation of Quantum Entanglement Over 143 km

Teleportation of entanglement over 143 km

Authors:

Herbst et al

Abstract:

As a direct consequence of the no-cloning theorem, the deterministic amplification as in classical communication is impossible for unknown quantum states. This calls for more advanced techniques in a future global quantum network, e.g., for cloud quantum computing. A unique solution is the teleportation of an entangled state, i.e., entanglement swapping, representing the central resource to relay entanglement between distant nodes. Together with entanglement purification and a quantum memory it constitutes a so-called quantum repeater. Since the aforementioned building blocks have been individually demonstrated in laboratory setups only, the applicability of the required technology in real-world scenarios remained to be proven. Here we present a free-space entanglement-swapping experiment between the Canary Islands of La Palma and Tenerife, verifying the presence of quantum entanglement between two previously independent photons separated by 143 km. We obtained an expectation value for the entanglement-witness operator, more than 6 SDs beyond the classical limit. By consecutive generation of the two required photon pairs and space-like separation of the relevant measurement events, we also showed the feasibility of the swapping protocol in a long-distance scenario, where the independence of the nodes is highly demanded. Because our results already allow for efficient implementation of entanglement purification, we anticipate our research to lay the ground for a fully fledged quantum repeater over a realistic high-loss and even turbulent quantum channel.

NIST Scientists Break Record for Quantum Teleportation

A new record distance has been set for the quantum teleportation of information over optical fibers. Researchers working at the National Institute of Standards and Technology (NIST) claim to have transmitted the quantum information carried in light particles over 100 km (62 miles), four times farther than previously achieved.

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Quantum Teleportation can Transfer two Properties With Fidelity

Suppose you see a beautiful table in a museum and you would like to have the same one at home. What could you do? One strategy is to accurately measure all its properties — its form (length, height and width) and its appearance (material and colour) — and then reproduce an identical copy for your living room. But this 'measure-and-reproduce' strategy would fail if the table were a quantum particle, such as a photon or an electron orbiting an atomic nucleus. The no-cloning theorem of quantum mechanics tells us that it is impossible to copy such a particle perfectly. On page 516 of this issue, Wang et al. show how to get around this apparent limitation of quantum physics. In a beautiful extension of previous experiments, they demonstrate how to transfer the values of two properties of a photon — the spin angular momentum (the direction of the photon's electric field, generally referred to as polarization) and the orbital angular momentum (which depends on the field distribution) — through quantum teleportation onto another photon.

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Prototype Quantum Radar Built

A prototype quantum radar that has the potential to detect objects which are invisible to conventional systems has been developed by an international research team led by a quantum information scientist at the University of York.

The new breed of radar is a hybrid system that uses quantum correlation between microwave and optical beams to detect objects of low reflectivity such as cancer cells or aircraft with a stealth capability. Because the quantum radar operates at much lower energies than conventional systems, it has the long-term potential for a range of applications in biomedicine including non-invasive NMR scans.

The research team led by Dr Stefano Pirandola, of the University's Department of Computer Science and the York Centre for Quantum Technologies, found that a special converter - a double-cavity device that couples the microwave beam to an optical beam using a nano-mechanical oscillator - was the key to the new system.

The device can either generate microwave-optical entanglement (during the signal emission) or convert a microwave into an optical beam (during the collection of the reflection beams from the object). The research is published in Physical Review Letters.

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Could Quantum Entanglement Increase a Particle's "Mass"

 [O]ne theorist has shown that an exotic quantum effect called entanglement has a real and measurable influence on a gravitational field— the first time this kind of link has ever been shown.

David Bruschi at the Hebrew University of Jerusalem in Israel says the new result has important implications for quantum mechanics and relativity and may represent an important step towards a long sought after theory that explains them both.

Bruschi’s idea is simple in principle. Physicists have long known that a single quantum particle can exist in two places at the same time. There is a clear quantum correlation called entanglement between these two locations that is well-defined mathematically in quantum mechanics.

Bruschi’s new approach is to formulate the mathematics in the context of relativity. He first makes the mathematical assumption that some perturbation of a gravitational field is possible in these circumstances.

He then goes on to formulate the mathematical properties of this perturbation and how they evolve when the two locations are maximally entangled and when they are not, a state known as maximally mixed.

He finds that the perturbation is zero when the states are maximally mixed. But in the other case— when the two locations are maximally entangled— the perturbation spreads through space over a scale related to the energy of the particle and the coherence time of the entanglement.

This kind of perturbation is mathematically similar to a gravitational wave, albeit on a much smaller scale. It is essentially equivalent to the particle having some additional weight. And that is what makes it potentially detectable.

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Quantum Entangled Particle Distribution via Satellite

Entanglement over global distances via quantum repeaters with satellite links

Authors:

Boone et al

Abstract:

We study entanglement creation over global distances based on a quantum repeater architecture that uses low-earth orbit satellites equipped with entangled photon sources, as well as ground stations equipped with quantum non-demolition detectors and quantum memories. We show that this approach allows entanglement creation at viable rates over distances that are inaccessible via direct transmission through optical fibers or even from very distant satellites.

pop sci write up.

Charlie Stross Called and Wants his Singularity Sky Concept Back

One possible future for communication is to create a quantum version of the internet that will have the ability, among other things, to send information with perfect security. This network will use entangled photons to transmit information from one locations to another without it passing through the space in between, hence the security.

Photons can only travel hundred kilometres or so through optical fibres before being absorbed. Conventional optical networks get around this with repeaters that boost the optical signal as it passes by.

This is more difficult with a quantum network but physicists have already tested many of the building blocks necessary to make quantum repeaters work. Nevertheless, quantum repeaters will be delicate pieces of kit, operating close to absolute zero with all the necessary cooling and power that is also required.

That should be relatively straightforward for quantum networks that stretch across land. But it is entirely unsuitable for undersea cables where conditions are far more hostile and the absence of infrastructure is a potential showstopper.

In fact, nobody is quite sure how it will be possible to operate the number of quantum repeaters necessary to carry one half of an entangled photon pair across the Atlantic or the Pacific. And without any technology even on the horizon that can do this job, there is a very real possibility that the quantum Internet might only ever consist of isolated quantum islands on different continents.

Today, Simon Devitt from Ochanomizu University in Japan and a few pals have come up with a way to solve this problem. Their idea is to transport the quantum bits or qubits across the ocean on a containership, a kind of quantum Clipper, that will shuttle back and forth across the seas with a ghostly quantum load.

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Quantum Imaging With Undetected Photons

Quantum imaging with undetected photons

Authors:

Lemos et al

Abstract:

Information is central to quantum mechanics. In particular, quantum interference occurs only if there exists no information to distinguish between the superposed states. The mere possibility of obtaining information that could distinguish between overlapping states inhibits quantum interference. Here we introduce and experimentally demonstrate a quantum imaging concept based on induced coherence without induced emission. Our experiment uses two separate down-conversion nonlinear crystals (numbered NL1 and NL2), each illuminated by the same pump laser, creating one pair of photons (denoted idler and signal). If the photon pair is created in NL1, one photon (the idler) passes through the object to be imaged and is overlapped with the idler amplitude created in NL2, its source thus being undefined. Interference of the signal amplitudes coming from the two crystals then reveals the image of the object. The photons that pass through the imaged object (idler photons from NL1) are never detected, while we obtain images exclusively with the signal photons (from NL1 and NL2), which do not interact with the object. Our experiment is fundamentally different from previous quantum imaging techniques, such as interaction-free imaging or ghost imaging, because now the photons used to illuminate the object do not have to be detected at all and no coincidence detection is necessary. This enables the probe wavelength to be chosen in a range for which suitable detectors are not available. To illustrate this, we show images of objects that are either opaque or invisible to the detected photons. Our experiment is a prototype in quantum information—knowledge can be extracted by, and about, a photon that is never detected.

Quantum Hacking: The Latest Concern in Cybersecurity

Quantum hacking is the latest fear in the world of information security. Not so long ago, physicists were claiming that they could send information with perfect security using a technique known as quantum key distribution.

This uses the laws of quantum mechanics to guarantee perfectly secure communication. And perfectly secure communication is what you get, at least in theory.

The trouble is that in practice the equipment used to carry out quantum key distribution has a number of weaknesses that an eavesdropper can exploit to gain information about the messages being sent. Various groups have demonstrated how quantum hacking presents a real threat to “perfectly secure” communication.

So in the cat and mouse game of information security, physicists have been fighting back by designing equipment that is more secure. Today, Nitin Jain at the Max Planck Institute for the Science of Light in Erlangen, Germany, and a few pals show how the changes still leave the equipment open to attack but at the same time reveal how the next generation of quantum cryptography could be made better.

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A Step Forward in Quantum Routing

The prospect of a quantum Internet has excited physicists for two decades. A quantum Internet will allow the transmission of information around the world with perfect security and make cloud-based quantum computing a reality.

But first, physicists must perfect the technology of quantum routing—the ability to receive and transmit quantum information without destroying it.

That’s a significant challenge. The key is a technique called quantum teleportation, which transmits information from one point to another without it passing through the space in between. This is a routine operation in any decent quantum optics lab but quantum routing—which concatenates the process—is another challenge altogether.

Today, Wolfgang Pfaff at the Kavli Institute of Nanoscience Delft in the Netherlands and a few pals say they’ve take a significant step toward this goal with the first demonstration of diamond teleporters that can act as nodes in a quantum network. “These results establish diamond spin qubits as a prime candidate for the realization of quantum networks for quantum communication and network-based quantum computing,” they say.

The fundamental difficulty in quantum routing is that quantum information is fragile stuff. So quantum teleportation has always involved creating a qubit, teleporting it and then immediately measuring it to check whether teleportation has been successful.

However, the process of measurement destroys quantum information. So an important goal is to create routers that can read and write quantum information without destroying it.

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Steps to a Quantum Internet

Using Quantum Entanglement to Teleport Energy

Teleportation is the transfer of an object from one point in the universe to another without travelling through the space in between. It is common practice in many labs around the world. Since the early 90s, physicists have used it to teleport increasingly complex objects starting with photons and more recently with atoms and ions.

But that’s just the beginning. Back in 2010, we looked at the extraordinary work of Masahiro Hotta at Tohoku University in Japan who has worked out that it ought to be possible to teleport energy too. That’s something that could have profound implications for the way quantum devices and machines might be made to work in future.

But energy teleportation has an important limitation–the distance over which it can be sent. The limitations are so severe that it’s hard to see how energy teleportation could help even at the nanoscale. This “strong distance limitation has hampered experimental verification,” says Hotta.

But now he and a couple of mates say they’ve discovered a way round this limitation that allows energy to be teleported over almost any distance. And this new protocol for energy teleportation should allow experimental verification for the first time.

First some background. Energy teleportation relies on the natural quantum variations that occur in a vacuum on the smallest scale. On this scale, a vacuum is far from empty.

Instead, physicists think of it as a maelstrom of virtual quantum particles and antiparticles constantly leaping in and out of existence. That’s OK and does not violate any physical laws as long as the average energy of this vacuum is zero.

It also ensures that regions of space are entangled over these short distances. So what happens in one region immediately influences the region it is entangled with.

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One Time Use Memory Through Quantum Entanglement

Computer security systems may one day get a boost from quantum physics, as a result of recent research from the National Institute of Standards and Technology (NIST). Computer scientist Yi-Kai Liu has devised away to make a security device that has proved notoriously difficult to build—a "one-shot" memory unit, whose contents can be read only a single time.

The research, which Liu is presenting at this week's Innovations in Theoretical Computer Science conference,* shows in theory how the laws of quantum physics could allow for the construction of such memory devices. One-shot memories would have a wide range of possible applications such as protecting the transfer of large sums of money electronically. A one-shot memory might contain two authorization codes: one that credits the recipient's bank account and one that credits the sender's bank account, in case the transfer is canceled. Crucially, the memory could only be read once, so only one of the codes can be retrieved, and hence, only one of the two actions can be performed—not both.

"When an adversary has physical control of a device—such as a stolen cell phone—software defenses alone aren't enough; we need to use tamper-resistant hardware to provide security," Liu says. "Moreover, to protect critical systems, we don't want to rely too much on complex defenses that might still get hacked. It's better if we can rely on fundamental laws of nature, which are unassailable."

Unfortunately, there is no fundamental solution to the problem of building tamper-resistant chips, at least not using classical physics alone. So scientists have tried involving quantum mechanics as well, because information that is encoded into a quantum system behaves differently from a classical system.

Liu is exploring one approach, which stores data using quantum bits, or "qubits," which use quantum properties such as magnetic spin to represent digital information. Using a technique called "conjugate coding, "two secret messages—such as separate authorization codes—can be encoded into the same string of qubits, so that a user can retrieve either one of the two messages. But as the qubits can only be read once, the user cannot retrieve both.

The risk in this approach stems from a more subtle quantum phenomenon: "entanglement," where two particles can affect each other even when separated by great distances. If an adversary is able to use entanglement, he can retrieve both messages at once, breaking the security of the scheme.

However, Liu has observed that in certain kinds of physical systems, it is very difficult to create and use entanglement, and shows in his paper that this obstacle turns out to be an advantage: Liu presents a mathematical proof that if an adversary is unable to use entanglement in his attack, that adversary will never be able to retrieve both messages from the qubits. Hence, if the right physical systems are used, the conjugate coding method is secure after all.

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Extraordinary Claim: Quantum Entanglement Appears to be Wormholes

Quantum entanglement, a perplexing phenomenon of quantum mechanics that Albert Einstein once referred to as "spooky action at a distance," could be even spookier than Einstein perceived.

Physicists at the University of Washington and Stony Brook University in New York believe the phenomenon might be intrinsically linked with wormholes, hypothetical features of space-time that in popular science fiction can provide a much-faster-than-light shortcut from one part of the universe to another.

But here's the catch: One couldn't actually travel, or even communicate, through these wormholes, said Andreas Karch, a UW physics professor.

Quantum entanglement occurs when a pair or a group of particles interact in ways that dictate that each particle's behavior is relative to the behavior of the others. In a pair of entangled particles, if one particle is observed to have a specific spin, for example, the other particle observed at the same time will have the opposite spin.

The "spooky" part is that, as research has confirmed, the relationship holds true no matter how far apart the particles are – across the room or across several galaxies. If the behavior of one particle changes, the behavior of both entangled particles changes simultaneously, no matter how far away they are.

Recent research indicated that the characteristics of a wormhole are the same as if two black holes were entangled, then pulled apart. Even if the black holes were on opposite sides of the universe, the wormhole would connect them.

Black holes, which can be as small as a single atom or many times larger than the sun, exist throughout the universe, but their gravitational pull is so strong that not even light can escape from them.

If two black holes were entangled, Karch said, a person outside the opening of one would not be able to see or communicate with someone just outside the opening of the other.

"The way you can communicate with each other is if you jump into your black hole, then the other person must jump into his black hole, and the interior world would be the same," he said.

The work demonstrates an equivalence between quantum mechanics, which deals with physical phenomena at very tiny scales, and classical geometry – "two different mathematical machineries to go after the same physical process," Karch said. The result is a tool scientists can use to develop broader understanding of entangled quantum systems.

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Where is the paper?!?! Must. Read.