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One of the quietest revolutions of our current century has been the entry of quantum mechanics into our everyday technology. It used to be that quantum effects were confined to physics laboratories and delicate experiments. But modern technology increasingly relies on quantum mechanics for its basic operation, and the importance of quantum effects will only grow in the decades to come. As such, physicist Miguel F. Morales has taken on the herculean task of explaining quantum mechanics to the rest of us laymen in this seven-part series (no math, we promise). Below is the fourth story in the series, but you can always find the starting story plus a landing page for the entire series thus far on site.

Beautiful telescopic images of our Universe are often associated with the stately, classical physics of Newton. While quantum mechanics dominates the microscopic world of atoms and quarks, the motions of planets and galaxies follow the majestic clockwork of classical physics.

But there is no natural limit to the size of quantum effects. If we look closely at the images produced by telescopes, we see the fingerprints of quantum mechanics. That’s because particles of light must travel across the vast reaches of space in a wave-like way to make the beautiful images we enjoy.

Enlarge (credit: Getty Images / Aurich Lawson)

One of the quietest revolutions of our current century has been the entry of quantum mechanics into our everyday technology. It used to be that quantum effects were confined to physics laboratories and delicate experiments. But modern technology increasingly relies on quantum mechanics for its basic operation, and the importance of quantum effects will only grow in the decades to come. As such, physicist Miguel F. Morales has taken on the herculean task of explaining quantum mechanics to the rest of us laymen in this seven-part series (no math, we promise). Below is the third story in the series, but you can always find the starting story here .

So far, we’ve seen particles move as waves and learned that a single particle can take multiple, widely separated paths. There are a number of questions that naturally arises from this behavior—one of them being, “How big is a particle?” The answer is remarkably subtle, and over the next two weeks (and articles) we'll explore different aspects of this question.

Today, we’ll start with a seemingly simple question: “How long is a particle?”

One of the quietest revolutions of our current century has been the entry of quantum mechanics into our everyday technology. It used to be that quantum effects were confined to physics laboratories and delicate experiments. But modern technology increasingly relies on quantum mechanics for its basic operation, and the importance of quantum effects will only grow in the decades to come. As such, physicist Miguel F. Morales has taken on the herculean task of explaining quantum mechanics to the rest of us laymen in this seven-part series ( no math , we promise). Below is the second story in the series, but you can always find the starting story here .

Welcome back for our second guided walk into the quantum mechanical woods! Last week, we saw how particles move like waves and hit like particles and how a single particle takes multiple paths. While surprising, this is a well-explored area of quantum mechanics—it is on the paved nature path around the visitor’s center.

This week I’d like to get off the paved trail and go a bit deeper into the woods in order to talk about how particles meld and combine while in motion. This is a topic that is usually reserved for physics majors; it's rarely discussed in popular articles. But the payoff is understanding how precision lidar works and getting to see one of the great inventions making it out of the lab, the optical comb. So let's go get our (quantum) hiking boots a little dirty—it'll be worth it.

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Today, quantum computing company D-Wave is announcing the availability of its next-generation quantum annealer, a specialized processor that uses quantum effects to solve optimization and minimization problems. The hardware itself isn't much of a surprise—D-Wave was discussing its details months ago —but D-Wave talked with Ars about the challenges of building a chip with over a million individual quantum devices. And the company is coupling the hardware's release to the availability of a new software stack that functions a bit like middleware between the quantum hardware and classical computers.

Quantum annealing

Quantum computers being built by companies like Google and IBM are general purpose, gate-based machines. They can solve any problem and should show a vast acceleration for specific classes of problems. Or they will, as soon as the gate count gets high enough. Right now, these quantum computers are limited to a few dozen gates and have no error correction. Bringing them up to the scale needed presents a series of difficult technical challenges.

D-Wave's machine is not general-purpose; it's technically a quantum annealer, not a quantum computer. It performs calculations that find low-energy states for different configurations of the hardware's quantum devices. As such, it will only work if a computing problem can be translated into an energy-minimization problem in one of the chip's possible configurations. That's not as limiting as it might sound, since many forms of optimization can be translated to an energy minimization problem, including things like complicated scheduling issues and protein structures.

Enlarge / Eugene Wigner. (credit: Denver Post Inc (Photo By David Cupp/The Denver Post via Getty Images))

Quantum mechanics, when examined closely, poses some deep questions about reality. These questions often take the form of thought experiments, which are later (usually much later) followed up by real experiments. One of the most difficult and deepest of these is a thought experiment proposed by Eugene Wigner in the 1960s, called "Wigner’s friend" (you don’t want to be Wigner’s friend). Now, much later, Wigner and his friend have been formalized and extended. The result sets us up with a contradiction: either reality is a lot stranger and less real at the level of quantum mechanics, or quantum states cannot possibly exist at large scales.

Don’t be Wigner’s friend

To understand why Wigner shouldn’t have any friends, we have to first dive into some details of quantum mechanics. Imagine measuring the spin of a single electron. Spin has an orientation in space, but it is not possible to measure that orientation. Instead, we have to choose an orientation and measure the spin along that orientation. So we might ask an electron if its spin is vertically upward or downward. The result (all else being equal) will be either up or down with 50 percent probability.

Let’s say we measure the spin and find that it is up. Any subsequent measurements will confirm it is up, as well. The measurement has defined the vertical spin component (a process often called wave function collapse). But it says nothing about the horizontal component of the spin—the horizontal component will remain in a superposition of left and right spins. That means that if we rotate our apparatus so that we are measuring spin left and right, the result will be random—the electron will be either spin-left or spin-right with 50 percent probability.