Entanglement...

Physicists take first-ever photo of quantum entanglement.
Credit: University of Glasgow/CC by 4.0

Topics: Einstein, Entanglement, Laser, Quantum Mechanics

Scientists just captured the first-ever photo of the phenomenon dubbed "spooky action at a distance" by Albert Einstein. That phenomenon, called quantum entanglement, describes a situation where particles can remain connected such that the physical properties of one will affect the other, no matter the distance (even miles) between them.

Einstein hated the idea, since it violated classical descriptions of the world. So he proposed one way that entanglement could coexist with classical physics — if there existed an unknown, "hidden" variable that acted as a messenger between the pair of entangled particles, keeping their fates entwined. [18 Times Quantum Particles Blew Our Minds in 2018]

There was just one problem: There was no way to test whether Einstein's view — or the stranger alternative, in which particles "communicate" faster than the speed of light and particles have no objective state until they are observed — was true. Finally, in the 1960s, physicist Sir John Bell came up with a test that disproves the existence of these hidden variables — which would mean that the quantum world is extremely weird.

This is "the pivotal test of quantum entanglement," said senior author Miles Padgett, who holds the Kelvin Chair of Natural Philosophy and is a professor of physics and astronomy at the University of Glasgow in Scotland. Though people have been using quantum entanglement and Bell's inequalities in applications such as quantum computing and cryptography, "this is the first time anyone has used a camera to confirm [it]."

To take the photo, Padgett and his team first had to entangle photons, or light particles, using a tried-and-true method. They hit a crystal with an ultraviolet (UV) laser, and some of those photons from the laser broke apart into two photons. "Due to conservation of both energy and momentum, each resulting pair [of] photons are entangled," Padgett said.

'Spooky' Quantum Entanglement Finally Captured in Stunning Photo
Yasemin Saplakoglu, Live Science

Coherent Spookiness...

Figure 1. See link below

Topics: Entanglement, Modern Physics, Quantum Mechanics, Research, Women in Science

One of the most counterintuitive aspects of quantum mechanics is its nonlocality: the encoding of information in the correlations between widely separated particles (see, for example, Physics Today, August 2017, page 14). Typical demonstrations of spatially extended entanglement involve pairwise entangled particles produced two by two. But in the spins of atoms coupled to an optical cavity, researchers have also created massively parallel correlations, which can extend over macroscopic distances. Until recently, the dynamics that give rise to those correlations have been inferred only from global measurements, such as the total magnetization of the atomic cloud. Now Monika Schleier-Smith and colleagues at Stanford University are combining nonlocal spin interactions with the capability to locally prepare and detect the atomic spin states.

Spin excitations in a cavity hop coherently over long distances
Johanna L. Miller, Physics Today

#P4TC related links:

"Spooky Action at a Distance"...October 1, 2011
"Spukhafte Fernwirkung..."March 9, 2012

Qubits Entanglement...

This photograph of the quantum device has components highlighted in false colour. The superconducting qubits are numbered 1–10 and the central bus resonator is labelled "B". The red and blue structures are control lines for the individual qubits. (Courtesy: Chao Song et al/ arXiv: 1703.10302)

Topics: Entanglement, Modern Physics, Quantum Computer, Quantum Mechanics

A group of physicists in China has taken the lead in the race to couple together increasing numbers of superconducting qubits. The researchers have shown that they can entangle 10 qubits connected to one another via a central resonator – so beating the previous record by one qubit – and say that their result paves the way to quantum simulators that can calculate the behaviour of small molecules and other quantum-mechanical systems much more efficiently than even the most powerful conventional computers.

Superconducting circuits create qubits by superimposing two electrical currents, and hold the promise of being able to fabricate many qubits on a single chip through the exploitation of silicon-based manufacturing technology. In the latest work, a multi-institutional group led by Jian-Wei Pan of the University of Science and Technology of China in Hefei, built a circuit consisting of 10 qubits, each half a millimetre across and made from slivers of aluminium laid on to a sapphire substrate. The qubits, which act as non-linear LC oscillators, are arranged in a circle around a component known as a bus resonator.

Initially, the qubits are put into a superposition state of two oscillating currents with different amplitudes by supplying each of them with a very low-energy microwave pulse. To avoid interference at this stage, each qubit is set to a different oscillation frequency. However, for the qubits to interact with one another, they need to have the same frequency. This is where the bus comes in. It allows qubits to transfer energy from one another, but does not absorb any of that energy itself.

Physics World: Ten superconducting qubits entangled by physicists in China
Edwin Cartlidge

7 Kilometers...

Calgary has seen quantum communication
brettA/Getty

Topics: Computer Science, Entanglement, Quantum Computer, Quantum Teleportation

A little math for perspective: 7 kilometers x 1,000 meters/1 kilometer x 39.37 inches/1 meter x 1 foot/12 inches x 1 mile/5,280 feet = 4.35 miles. Fiber optic cables typically have a range, and stations to repeat/boost the signals. This could be improved of course, and part of an infrastructure buildup that could spur the education industry K-12 and post secondary to prepare future workers for building a new communications architecture. A lot of automated and outsourced jobs are not coming back, and these likely wouldn't be frustrated by old money, like the fossil fuel industry does alternative energy.

A new world record for quantum teleportation has been set, bringing quantum communication networks that can stretch between cities a step closer. Two independent teams have transferred quantum information over several kilometres of fibre optic networks.

Being able to establish teleportation over long distances is a crucial step towards exchanging quantum cryptographic keys needed for encoding data sent over the fibres.

Quantum teleportation is a phenomenon in which the quantum states of one particle can be transferred to another, distant particle without anything physical traveling between them. It relies on a property called entanglement, in which measuring the state of one particle immediately affects the state of its entangled partner, regardless of the distance between them.

Conceptually, one way of doing teleportation involves three participants: say, Alice, Bob and Charlie. In order for Alice and Bob to exchange cryptographic keys, they have to first establish the capacity for teleportation, with Charlie’s help.

First Alice sends a particle (A) to Charlie. Bob, meanwhile, creates a pair of entangled particles (B & C), sends B to Charlie and holds on to C. Charlie receives both A and B, and measures the particles in such a way that it’s impossible to tell which particle was sent by Alice and which by Bob. This so-called Bell state measurement results in the quantum state of particle A being transferred to particle C, which is with Bob.

New Scientist:
Quantum teleportation over 7 kilometres of cables smashes record, Anil Ananthaswamy

AlN and Qbits...

This graphic illustrates an engineered nitrogen vacancy in aluminum nitride.

Topics: Computer Science, Entanglement, Materials Science, Quantum Computer, Quantum Mechanics, Schrödinger’s cat, Solid State Physics

I included a short primer on Aluminum Nitride if you're interested (which, I'm guessing if you're reading something this nerdy, you kinda are). If you're viewing this on a laptop, pad or a mobile phone, I'm 99.99999999% sure your devices chips were manufactured with AlN. If you go to the link below, the article gives a succinct description of quantum entanglement (when atoms due to their proximity to each other cannot be described as a single unit), and superposition - famously illustrated by the Schrödinger’s cat thought experiment, which is the whole POINT of a quantum computer: it could be "1"; "0" or both at the same time, called a superposition of states. Thankfully, a lot of smart brains are tasked with what shape our tech lives post-Silicon will take, with which we will promptly share more cute cat videos in a kind of weird, digital Freudian slip.

Quantum computers have the potential to break common cryptography techniques, search huge datasets and simulate quantum systems in a fraction of the time it would take today’s computers. But before this can happen, engineers need to be able to harness the properties of quantum bits or qubits.

Currently, one of the leading methods for creating qubits in materials involves exploiting the structural atomic defects in diamond. But several researchers at the University of Chicago and Argonne National Laboratory believe that if an analogue defect could be engineered into a less expensive material, the cost of manufacturing quantum technologies could be significantly reduced. Using supercomputers at the National Energy Research Scientific Computing Center (NERSC), which is located at the Lawrence Berkeley National Laboratory (Berkeley Lab), these researchers have identified a possible candidate in aluminum nitride. Their findings were published in Nature Scientific Reports.

NERSC: Could Aluminum Nitride Produce Quantum Bits? Linda Vu
Seo, H. et al. Design of defect spins in piezoelectric aluminum nitride for solid-state hybrid quantum technologies. Sci. Rep. 6, 20803; doi: 10.1038/srep20803 (2016).

Closing Bell's Loopholes...

Figure 2. The locality loophole arises from the possibility that hidden signals between Alice and Bob can influence the results of their measurements. This space–time diagram represents an entangled-photon experiment for which the loophole is closed. The diagonal lines denote light-speed trajectories: The paths of the entangled photons are shown in red, and the forward light cones of the measurement-basis choices are shown in blue. Note that Bob cannot receive information about Alice’s chosen basis until after his measurement is complete, and vice versa.

Citation: Phys. Today 69, 1, 14 (2016); http://dx.doi.org/10.1063/PT.3.3039

Topics: Bell's Theorem, Entanglement, Modern Physics, Quantum Mechanics, Theoretical Physics

The predictions of quantum mechanics are often difficult to reconcile with intuitions about the classical world. Whereas classical particles have well-defined positions and momenta, quantum wavefunctions give only the probability distributions of those quantities. What’s more, quantum theory posits that when two systems are entangled, a measurement on one instantly changes the wavefunction of the other, no matter how distant.

Might those counterintuitive effects be illusory? Perhaps quantum theory could be supplemented by a system of hidden variables that restore local realism, so every measurement’s outcome depends only on events in its past light cone. In a 1964 theorem John Bell showed that the question is not merely philosophical: By looking at the correlations in a series of measurements on widely separated systems, one can distinguish quantum mechanics from any local-realist theory. (See the article by Reinhold Bertlmann, Physics Today, July 2015, page 40.) Such Bell tests in the laboratory have come down on the side of quantum mechanics. But until recently, their experimental limitations have left open two important loopholes that require additional assumptions to definitively rule out local realism.

Now three groups have reported experiments that close both loopholes simultaneously. First, Ronald Hanson, Bas Hensen (both pictured in figure 1) [see link below], and their colleagues at Delft University of Technology performed a loophole-free Bell test using a novel entanglement-swapping scheme.¹ More recently, two groups—one led by Sae Woo Nam and Krister Shalm of NIST,² the other by Anton Zeilinger and Marissa Giustina of the University of Vienna³—used a more conventional setup with pairs of entangled photons generated at a central source.

Physics Today: Three groups close the loopholes in tests of Bell’s theorem
Johanna L. Miller

Qubits @ Room...

Physicists create many entangled states of electrons ("e") and nuclei ("n") in the industrially important semiconductor silicon carbide, all at ambient conditions. (Courtesy: Paul Klimov, University of Chicago)

Topics: Entanglement, Semiconductor Technology, Quantum Computer, Quantum Mechanics

The quantum entanglement of a large ensemble of spins in a semiconductor has been carried out at room temperature for the first time, by researchers in the US. The team entangled more than 10,000 copies of two-qubit entangled states in a commercial silicon-carbide (SiC) wafer at ambient conditions. SiC is widely used in electronics, so this latest achievement could be an important step towards the creation of sophisticated quantum devices that harness entanglement.

Entanglement is a purely quantum-mechanical phenomenon that allows two or more particles to have a much closer relationship than is allowed by classical physics, no matter how far apart they may be. The states of entangled particles are inextricably linked such that any change made to one particle instantly influences the state of the other. Entangled particles are seen as a key component of quantum computers, but for entanglement to be truly utilized in practical applications, researchers must be able to entangle quantum bits (qubits) at room temperature and preserve the entangled state.

Physics World: Physicists entangle qubits in a semiconductor at room temperature
Tushna Commissariat

Time and Entanglement...

Credit: Physics arXiv Blog; paper link below

Physics arXiv Blog: When the new ideas of quantum mechanics spread through science like wildfire in the first half of the 20th century, one of the first things physicists did was to apply them to gravity and general relativity. The result were not pretty.

It immediately became clear that these two foundations of modern physics were entirely incompatible. When physicists attempted to meld the approaches, the resulting equations were bedeviled with infinities making it impossible to make sense of the results.

Then in the mid-1960s, there was a breakthrough. The physicists John Wheeler and Bryce DeWitt successfully combined the previously incompatible ideas in a key result that has since become known as the Wheeler-DeWitt equation. This is important because it avoids the troublesome infinites—a huge advance.

But it didn't take physicists long to realise that while the Wheeler-DeWitt equation solved one significant problem, it introduced another. The new problem was that time played no role in this equation. In effect, it says that nothing ever happens in the universe, a prediction that is clearly at odds with the observational evidence.

This conundrum, which physicists call ‘the problem of time’, has proved to be thorn in flesh of modern physicists, who have tried to ignore it but with little success.

Then in 1983, the theorists Don Page and William Wooters came up with a novel solution based on the quantum phenomenon of entanglement. This is the exotic property in which two quantum particles share the same existence, even though they are physically separated.

Entanglement is a deep and powerful link and Page and Wooters showed how it can be used to measure time. Their idea was that the way a pair of entangled particles evolve is a kind of clock that can be used to measure change.

But the results depend on how the observation is made. One way to do this is to compare the change in the entangled particles with an external clock that is entirely independent of the universe. This is equivalent to god-like observer outside the universe measuring the evolution of the particles using an external clock.

In this case, Page and Wooters showed that the particles would appear entirely unchanging—that time would not exist in this scenario.

But there is another way to do it that gives a different result. This is for an observer inside the universe to compare the evolution of the particles with the rest of the universe. In this case, the internal observer would see a change and this difference in the evolution of entangled particles compared with everything else is an important a measure of time.

This is an elegant and powerful idea. It suggests that time is an emergent phenomenon that comes about because of the nature of entanglement. And it exists only for observers inside the universe. Any god-like observer outside sees a static, unchanging universe, just as the Wheeler-DeWitt equations predict.

Physics arXiv:
Quantum Experiment Shows How Time ‘Emerges’ from Entanglement