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Using light and optical fibres to send information from point A to B is today a standard practice, but what if we could skip the “sending and carrying” steps entirely and simply read information instantaneously? Thanks to quantum entanglement, this idea is no longer a work of fiction, but a subject of ongoing research. By entangling two quantum particles such as ions, scientists can put them into a fragile joint state where measuring one particle gives information about the other in ways that that would be impossible classically.

Researchers from the University of Innsbruck, Austria, have now performed this tricky entanglement process on two calcium ions trapped in optical cavities 230 m apart – equivalent to around two football pitches – and connected via a 520 m long optical fibre. This separation is a record for trapped ions and sets a milestone in quantum communication and computation systems based on these quantum particles.

Towards a quantum network

Quantum networks are the backbone of quantum communication systems. Among their attractions is that they could link the world with unprecedented computing power and security while enhancing precision sensing and time measurement for applications ranging from metrology to navigation. Such quantum networks would consist of quantum computers – the nodes – connected through the exchange of photons. This exchange can be done in free space, similarly to how light travels through space from the Sun to our eyes. Alternatively, the photons can be sent through optical fibres similar to those used to transmit data for Internet, television and phone services.

Quantum computers based on trapped ions offer a promising platform for quantum networks and quantum communication for two reasons. One is that their quantum states are relatively easy to control. The other is that these states are robust against external perturbations that can disrupt the information carried between and at the nodes.

Trapped calcium ions

In the latest work, research teams led by Tracy Northup and Ben Lanyon at Innsbruck trapped calcium ions in Paul traps – an electric field configuration that produces a force on the ion, confining it in the centre of the trap. Calcium ions are appealing because they have a simple electronic structure and are robust against noise. “They are compatible with technology needed for quantum networks; and they are also easily trapped and cooled, therefore suited for scalable quantum networks,” explains Maria Galli, a PhD student at Innsbruck who was involved in the work, which is described in Physical Review Letters.

The researchers began by placing a single trapped ion inside each of two separate optical cavities. These cavities are spaces between pairs of mirrors that allow precise control and tuning of the frequency of light that bounces between them (see image above). This tight control is crucial for linking, or entangling, the information of the ion to that of the photon.

After entangling the ion-photon system at each of the two cavities – the nodes of the network – the researchers performed a measurement to characterize the entangled system. While the measurement destroys the entanglement, the researchers had to repeat this process multiple times to optimize this step. The photons, each entangled with one of the calcium ions, are then transmitted through the optical fibre that connects the two nodes, which are located in separate buildings.

Team effort: Tracy Northup and Ben Lanyon with their respective teams, photographed at the Institute for Quantum Optics and Quantum Information (IQOQI) campus in Innsbruck. (Courtesy: Innsbruck Quantum Network team)

Exchanging information

While the researchers could have transferred the photons in free space, doing so would have risked disrupting the ion-photon entanglement due to several noise sources. Optical fibres, in contrast, are low loss, and they also shield the photons and preserves their polarization, allowing longer separation between the nodes. However, they are not ideal. “We did observe some drifts in the polarization. For this reason, every 20 minutes we would characterize the polarization rotation of the fibre and correct for it.” says Galli.

The two photons exchange the information of their respective ion-photon systems through a process known as a photon Bell-state measurement (PBSM). In this state-selective detection technique, the photons’ wavefunctions are overlapped, creating an interference pattern that can be measured with four photodetectors.

By reading the measured signals on the photodetectors, the researchers can tell whether the information carried by the photons – their polarization state – is identical or not. Matching pairs of outcomes (either horizontal or vertical polarization states) consequently herald the generation of entanglement between the remote ions.

Trade-offs for successful entanglement

The researchers had to balance several factors to generate entanglement between the ions. One is the time window in which they do the final joint measurement of the photons. The longer this time window is, the more chance the researchers have of detecting photons – but the trade-off is that the ions are less entangled. This is because they aim to catch photons that arrive at the same time, and allowing a longer time window could lead them to detect photons that actually arrived at different times.

The researchers therefore needed to carefully check how much entanglement they managed to achieve for a given time window. Over a time window of 1 microsecond, they repeated the experiment more than 13 million times, producing 555 detection events. They then measured the state of the ions at each node independently to check the correlation, which was 88%. “Our final measurement step is in fact to measure the state of both ions to verify that the expected state correlation is there,” Galli says. “This confirms that we have succeeded in creating entanglement between the two ions.”

From a sprint to a marathon

Two football pitches may seem like a large distance over which to create a precarious quantum entangled state, but the Innsbruck team has bigger plans. By making changes such as increasing the wavelength of photons used to transmit information between the ions, the researchers hope to cover a much greater distance of 50km – longer than a marathon.

While other research groups have previously demonstrated entanglement over even longer distances using neutral atoms, ion-based platforms have certain advantages. Galli notes that the fidelities of quantum gates performed with trapped ions are better than those of quantum gates performed on atoms, mainly because interactions between ions are stronger and more stable than interactions between atoms and the coherence time of ions is much longer.

The post Entangled ions set long-distance record appeared first on Physics World.

The laws of physics allow time travel. So why haven’t people become chronological hoppers?

It’s not an exaggeration to say that every major advance in physics for more than a century has turned on revelations about symmetry. It’s there at the dawn of general relativity, in the birth of the Standard Model, in the hunt for the Higgs. For that reason, research across physics is now building to a crescendo. It was touched off by a 2014 paper, “Generalized Global Symmetries…

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The strange phenomenon of quantum tunneling has been observed in a chemical reaction that defies classical physics

Insider Brief An Imperial College-led team of researchers were able to create a time-domain version of the double-slit experiment. The team used a beam of light that was twice gated in time — and discovered many more oscillations than predicted, suggesting a rise time that approached an optical cycle. Results could yield practical advances, such […]

By studying an artificial neural network, researchers in the US may have gained a better understanding of how and why our memories fade over time. Led by Ulises Pereira-Obilinovic at New York University, the team has found evidence that the stable, repeating neural patterns associated with newer memories transform into more chaotic patterns over time, and eventually fade to random noise. This could be a mechanism used by our brains to clear space for new memories.

In some models of the brain, memories are stored in repeating patterns of information exchange called “attractor networks”. These form within webs of interconnected nodes that are used to represent the neurons in our brains.

These nodes convey information by emitting signals at specific firing rates. Nodes that receive signals will then generate their own signals, thereby exchanging information with their neighbours. The strengths of these exchanges are weighted by the degree of synchronization between pairs of nodes.

Stable patterns

Attractor networks form as an external input is applied to a neural network, which assigns an initial firing rate to each of its nodes. These frequencies evolve as the weights between different pairs of nodes readjust themselves, and eventually settle into stable, repeating patterns.

To retrieve a memory, researchers can then apply an external cue that is similar to the original input, which kicks the neural network into the relevant attractor network. Multiple memories can be imprinted onto a single neural network, which naturally switches between stable attractor networks over time – until an external cue is provided.

These systems have their limits, however. If too many attractor networks are stored on the same neural network, it may suddenly become too noisy for any of them to be retrieved, and all its memories will be forgotten at once.

Losing memories

To prevent this from happening, Pereira-Obilinovic’s team suggest that our brains must have evolved a mechanism for losing memories over time. To test this theory, the trio, which also included Johnatan Aljadeff at the University of Chicago, and Nicolas Brunel at Duke University, simulated neural networks in which the weights between connected nodes in an attractor network will gradually diminish as new memories are imprinted.

They found that this caused older attractor networks to shift into more chaotic states over time. These networks featured faster fluctuating patterns. These patterns of firing signals never perfectly repeat, and can coexist far better with newer, stable attractor networks. Eventually, this increasing randomness causes older attractor networks to fade into random noise, and the memory they carry is forgotten.

Altogether, the researchers hope their theory could help to explain how our minds are able to constantly take in new information, at the price of losing older memories. Their insights could help neurologist to better understands how our brains store and retrieve memories, and why they ultimately fade over time.

The research is described in Physical Review X.

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A novel quantum computing technique could be able to reconstitute a small object across space "without any particles crossing," just like a wormhole.

Humans may have gotten one step closer to figuring out how to make wormholes thanks to fascinating new research.

That’s at least according to Hatim Saleh, a research fellow at the University of Bristol and co-founder of the startup DotQuantum, who claims to have invented what he calls “counterportation,” which “provides the first-ever practical blueprint for creating in the lab a wormhole that verifiably bridges space,” according to a statement.

Published in the journal Quantum Science and Technology, Saleh’s research focused on a novel quantum computing technique that should — at least on paper — be able to reconstitute a small object across space “without any particles crossing.”

While it’s an exciting prospect, realizing his vision will require a lot more time and effort — not to mention next-generation quantum computers that haven’t been designed, let alone built yet. That is if it’s even possible at all.

Counterportation can be achieved, the study suggests, by the construction of a small “local wormhole” in a lab — and as the press release notes, plans are already underway to actually build the groundbreaking technology described in the paper.

While it sounds a lot like teleportation, Saleh noted that it’s not quite the same thing.

“While counterportation achieves the end goal of teleportation, namely disembodied transport, it remarkably does so without any detectable information carriers traveling across,” the quantum expert said.

The concept relies on a unique aspect of quantum physics called quantum entanglement, which allows “entirely separate quantum particles” to “be correlated without ever interacting,” as University of Bristol optical communication systems professor John Rarity explained in the statement.

“This correlation at a distance can then be used to transport quantum information (qubits) from one location to another without a particle having to traverse the space, creating what could be called a traversable wormhole,” he added.

To make counterportation a reality, however, is going to take a whole lot more research — and future breakthroughs in the quantum computing field.

“If counterportation is to be realized, an entirely new type of quantum computer has to be built: an exchange-free one, where communicating parties exchange no particles,” said Saleh.

Unfortunately, these machines are still a distant dream as “no one yet knows how to build” them, Saleh admitted.

When and if this exchange-free quantum computer is built, per the researcher, it could prove revolutionary in the field.

“By contrast to large-scale quantum computers that promise remarkable speed-ups, which no one yet knows how to build, the promise of exchange-free quantum computers of even the smallest scale is to make seemingly impossible tasks — such as counterportation — possible, by incorporating space in a fundamental way alongside time,” Saleh boasted.

While this definitely sounds like something out of the plot of the 2014 film “Interstellar,” reconstituting small objects by leveraging the weirdness of the quantum world is an exciting proposition whether it’s a long shot or not.

More on wormholes: Objects We Thought Were Black Holes May Actually Be Wormholes, Scientists Say

The post Researchers Say They’ve Come Up With a Blueprint for Creating a Wormhole in a Lab appeared first on Futurism.

A new thought experiment suggests that the mere presence of a black hole can destroy a nearby quantum spatial superposition. Developed by physicists in the US, the experiment implies that the long-range gravitational field of the particle in the superposition will interact with the black hole’s event horizon, causing cause the quantum superposition to decohere within finite time.

Coherence is a concept in quantum mechanics that allows a system to exist in a superposition of several different quantum states at the same time. Decoherence is the process of destroying a superposition by making a measurement that puts the system into a specific state. Measurement in this case is a general term and refers to an interaction between a quantum system and its surroundings. A measurement could, for example, be a stray magnetic field or a fluctuation in temperature as well as a lab-based determination of a property of the system (such as the polarization of a photon).

Superposition and other aspects of quantum mechanics do a fantastic job of describing the behaviour of microscopic systems. However, physicists have not been able to incorporate gravity into quantum theory’s description of nature. Today, gravity is best described by Albert Einstein’s general theory of relativity and unifying the two theories in a theory of quantum gravity is an important aim of modern physics. However, this has proven very difficult because the effects of quantum gravity are only expected to be relevant at very short length scales corresponding to extremely high energies – which are well beyond the capabilities of current and future particle accelerators.

Quantum thinking

Because real experiments cannot be done, physicists use thought experiments to try to develop a consistent theory of quantum gravity. These seek to understand the behaviour of quantum systems under extreme gravitational conditions such as those that exist at the event horizon of a black hole. This is a boundary surrounding a black hole, beyond which nothing – not even light – can escape the black hole’s immense gravitational field. This implies that information can enter a black hole, but it cannot leave.

This latest thought experiment has been devised by physicists at the University of Chicago and Princeton University and is described in a preprint on the arXiv server. Co-author Daine Danielson says that the experiment considers a hidden observer behind a black hole’s event horizon.

The thought experiment involves a massive particle, such as an electron, that is fired at barrier that contains two slits. According to quantum mechanics, the electron will behave as a wave that diffracts through both slits simultaneously. In other words, the electron is in a coherent spatial superposition of two states, each travelling through its own slit. If the electrons strike a screen behind the slits, the two states are recombined and create an interference pattern.

Alice and Bob

The new thought experiment describes a double-slit experiment that is conducted near to a black hole by a physicist called Alice. There is also an observer called Bob who is inside the black hole.

As Alice conducts her double slit experiment, a quantum theory of gravity requires that the massive particle interacts with the black hole via “soft gravitons”. Gravitons are hypothetical carriers of the gravitational field and are analogous to photons – which are carriers of the electromagnetic field.

These soft gravitons can be absorbed by the black hole, where they can be measured by Bob – at least in principle. By making multiple measurements of soft gravitons over time, Bob should be able to deduce the state of the quantum superposition in Alice’s experiment. In other words, Bob is making a measurement on Alice’s experiment from beyond the black hole’s event horizon, from where he is causing the spatial superposition to decohere.

Causal paradox

Therein lies the paradox. How can Bob decohere Alice’s experiment if information cannot travel out of the event horizon? Indeed, doing so violates causality. Danielson and colleagues argue that this paradox can only be resolved if the black hole itself decoheres Alice’s experiment before Bob can.

In other words, they say, the black hole affects the quantum superposition in the same way as a classical observer. “Here, we have a precise situation where the geometry of the universe itself is giving a ‘definiteness’ to a quantum superposition,” Danielson says.

In their paper, the researchers argue that their analysis also applies to other types of horizons, such as the cosmological horizon – which defines the size of the observable universe. Such thought experiments are useful for probing the fundamental rules that a consistent theory of quantum gravity may one day have, the researchers say. “Any theory of quantum gravity, for example, must have the fundamental feature that black holes which act as quantum systems act as observers,” says co-author Gautam Satishchandran.

Vlatko Vedral, a quantum physicist at the University of Oxford, says that he has reservations about some of the treatments in the paper. He says that the superposition is treated quantum mechanically, but the authors treat the background gravitational field – such as the black hole itself – classically. “It’s not clear that an approximation like this is valid in the context they consider,” he says. However, if the conclusions are correct, Vedral considers them to be profound. The thought experiment suggests that black holes can serve as a source of irreversibility – the destruction of a quantum state that can never be fully recovered. Since gravitation is infinitely long-range, it does not matter how far an experiment is from a black hole, he says, the decoherence effect that the authors calculate would be non-zero. Therefore, the creation and recombination of quantum spatial superpositions can never be fully efficient because “part of [the system] is always irreversibly lost to beyond the horizon,” he says.

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An international team of scientists claim to have found a way to speed up, slow down, and even reverse the flow of time for a given quantum system.

An international team of scientists claim to have found a way to speed up, slow down, and even reverse the clock of a given system by taking advantage of the unusual properties of the quantum world, Spanish newspaper El País reports.

In a series of six papers, the team from the Austrian Academy of Sciences and the University of Vienna detailed their findings. The familiar laws of physics don’t map intuitively onto the subatomic world, which is made up of quantum particles called qubits that can technically exist in more than one state simultaneously, a phenomenon known as quantum entanglement.

Now, the researchers say they’ve figured out how to turn these quantum particles’ clocks forward and backward.

“In a theater, [classical physics], a movie is projected from beginning to end, regardless of what the audience wants,” Miguel Navascués, a researcher at the Austrian Academy of Sciences’ Institute of Quantum Optics and Quantum Information who worked on the research, told El País.

“But at home [the quantum world], we have a remote control to manipulate the movie,” he added. “We can rewind to a previous scene or skip several scenes ahead.”

“We have made science fiction come true!” the researcher exclaimed.

By developing a “rewind protocol,” the team says they were able to revert an electron to a previous state. In experiments, they say they were able to demonstrate the use of a quantum switch to revert a photon to its original state before passing through a crystal.

While it’s an exciting prospect, scaling up the technique could prove extremely difficult, if not impossible.

“If we could lock a person in a box with zero external influences, it would be theoretically possible,” Navascués told El País. “But with our currently available protocols, the probability of success would be very, very low.”

And there’s an even bigger catch as well.

“Also, the time needed to complete the process depends on the amount of information the system can store,” Navascués added. “A human being is a physical system that contains an enormous amount of information. It would take millions of years to rejuvenate a person for less than a second, so it doesn’t make sense.”

Besides, the system is only able to revert the state of a given particle. To speed up time, though, the researchers have an ace up their sleeves.

“We discovered that you can transfer evolutionary time between identical physical systems,” Navascués explained. “In a year-long experiment with ten systems, you can steal one year from each of the first nine systems and give them all to the tenth.”

Instead of recreating “Back to the Future,” the researchers see more mundane practical applications of their discovery. For instance, qubit states of a quantum processor could be reversed, effectively allowing researchers to undo errors during their development.

More on the quantum world: Aliens May Be Creating Black Holes to Store Quantum Information, Scientists Say

The post Scientists Say They Can Reverse Time in a Quantum System appeared first on Futurism.

For their latest magic trick, physicists have done the quantum equivalent of conjuring energy out of thin air. It’s a feat that seems to fly in the face of physical law and common sense. “You can’t extract energy directly from the vacuum because there’s nothing there to give,” said William Unruh, a theoretical physicist at the University of British Columbia, describing the standard way of thinking.