Lifeboat Foundation

Quantum communication is a strange beast, but one of the weirdest proposed forms of it is called counterfactual communication — a type of quantum communication where no particles travel between two recipients.

Theoretical physicists have long proposed that such a form of communication would be possible, but now, for the first time, researchers have been able to experimentally achieve it — transferring a black and white bitmap image from one location to another without sending any physical particles.

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For the first time, scientists have subjected quantum entanglement to extreme levels of acceleration, and there’s nothing fragile about this “spooky action at a distance” - it’s way more robust than we thought.

In recent experiments, entangled particles held firm even while being accelerated to 30g — 30 times Earth’s acceleration — and the results could have a big impact on our search for a unified theory of modern physics.

“These experiments shall help [us] unify the theories of quantum mechanics and relativity,” says one of the team, Rupert Ursin, from the University of Vienna, Austria.

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Quantum computing could outsmart current computing for complex problem solving, but only if scientists figure out how to make it practical. A Stanford team is investigating new materials that could become the basis for such an advance.

If it proves true, it could heal the rift between quantum mechanics and the theory of relativity.

Quantum computers finally seem to be coming of age with promises of “quantum supremacy” by the end of the year. But there’s a problem—very few people know how to work them.

The bold claim of achieving “quantum supremacy” came on the back of Google unveiling a new quantum chip design. The hyperbolic phrase essentially means building a quantum device that can perform a calculation impossible for any conventional computer.

In theory, quantum computers can crush conventional ones at important tasks like factoring large numbers. That’s because unlike normal computers, whose bits can either be represented as 0 or 1, a quantum bit—or “qubit”—can be simultaneously 0 and 1 thanks to a phenomenon known as superposition.

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Quantum entanglement, one of the most intriguing features of multi-particle quantum systems, has become a fundamental building block in both quantum information processing and quantum computation. If two particles are entangled, no matter how far away they are separated, quantum mechanics predicts that measurement of one particle leads to instantaneous wave-function collapse of the other particle.

Such “spooky action at a distance” is non-intuitive, and in 1935, Einstein attempted to use entanglement to criticize quantum mechanics to suggest that the quantum description of physical reality is incomplete. Einstein believed that no information could travel faster than light, and suggested that there might be some local hidden variable theories that could explain the world in a deterministic way, if and only if they obey realism and locality. In 1964, J. S. Bell showed that the debate can be experimentally resolved by testing an inequality; by measuring correlations between entangled parties, the result calculated from local hidden variable theories should be constrained by the Bell inequality, which, on the other hand, can be violated in the predictions of quantum mechanics.

By reducing the velocity of light dramatically, researchers at the Hong Kong University of Science and Technology implemented a Bell Test and were able to generate frequency-bin entangled narrowband biphotons from spontaneous four-wave mixing (SFWM) in cold atoms with a double-path configuration, where the phase difference between the two spatial paths can be controlled independently and nonlocally.

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(Phys.org)—In the non-intuitive quantum domain, the phenomenon of counterfactuality is defined as the transfer of a quantum state from one site to another without any quantum or classical particle transmitted between them. Counterfactuality requires a quantum channel between sites, which means that there exists a tiny probability that a quantum particle will cross the channel—in that event, the run of the system is discarded and a new one begins. It works because of the wave-particle duality that is fundamental to particle physics: Particles can be described by wave function alone.

Well understood as a workable scheme by physicists, theoretical aspects of counterfactual communication have appeared in journals, but until recently, there have been no practical demonstrations of the phenomenon. Now, a collaborative of Chinese scientists has designed and experimentally tested a counterfactual communication system that successfully transferred a monochrome bitmap from one location to another using a nested version of the quantum Zeno effect. They have reported their results in the Proceedings of the National Academy of Sciences.

The quantum Zeno effect occurs when an unstable quantum system is subjected to a series of weak measurements. Unstable particles can never decay while they are being measured, and the system is effectively frozen with a very high probability. This is one of the implications of the well known but highly non-intuitive principle that looking at something changes it in the quantum realm.

Einstein’s “spooky action at a distance” persists even at high accelerations, researchers of the Austrian Academy of Sciences and the University of Vienna were able to show in a new experiment. A source of entangled photon pairs was exposed to massive stress: The photons’ entanglement survived the drop in a fall tower as well as 30 times the Earth’s gravitational acceleration in a centrifuge. This was reported in the most recent issue of Nature Communications. The experiment helps deepen our understanding of quantum mechanics and at the same time gives valuable results for quantum experiments in space.

Einstein’s theory of relativity and the theory of quantum mechanics are two important pillars of modern physics. On the way of achieving a “Theory of Everything,” these two theories have to be unified. This has not been achieved as of today, since phenomena of both theories can hardly be observed simultaneously. A typical example of a quantum mechanical phenomenon is entanglement: This means that the measurement of one of a pair of light particles, so-called photons, defines the state of the other particle immediately, regardless of their separation. High accelerations on the other hand can best be described by the theory of relativity. Now for the first time, quantum technologies enable us to observe these phenomena at once: The stability of quantum mechanical entanglement of photon pairs can be tested while the photons undergo relativistically relevant acceleration.

If we want to find extra dimensions lurking within our Universe — something that string theory attempts to explain — gravitational waves could be our key to locating them, physicists suggest.

This new hypothesis seeks to answer the long-standing mystery of why gravity appears to be weaker than the other fundamental forces in our Universe, by proposing that it’s actually ‘leaking out’ into extra dimensions we’re yet to detect.

“Extra dimensions have been discussed for a long time from different points of view,” Emilian Dudas from the École Polytechnique in France, who wasn’t involved in the study, told Leah Crane at New Scientist.

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