A Remarkable Observer Guide to Quantum Mechanics, pt 7: The Quantum Century

A Remarkable Observer Guide to Quantum Mechanics, pt 7: The Quantum Century

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One of the quietest revolutions of our present century was the entry of quantum mechanics into our everyday technology. It was previously that quantum effects were limited to physics laboratories and delicate experiments. But modern technology is increasingly relying on quantum mechanics for its basic operation, and the importance of quantum effects will only grow in the coming decades. As such, the physicist Miguel F. Morales took on the great task of explaining quantum mechanics to laymen in this seven-part series (no mathematics, we promise). Below is the series finale, but you can always find the start story plus a landing page for the entire series on site.

The future is already here – it’s just not evenly distributed –William Gibson

As tool builders, we have only been able to use quantum mechanics recently. Understanding and manipulating quantum devices was like getting an intoxicating new superpower – there are so many things we can build now that would have been impossible a few years ago.

We have encountered some of these quantum technologies in previous articles. Some of them, like the quantum dots in TVs, are already becoming commonplace; others exist, such as optical watches, but are still very rare.

Since this is the last article in this series, I want to look at a near future where quantum technologies are likely to add to our everyday existence. One does not have to look far – all the technologies we are going to explore today already exist. Most of them are still rare, isolated in laboratories or as technology demonstrators. Others hide in the face, such as the MRI machine at the local hospital or the hard drive sitting on your desk. Let us focus in this article on some of the technologies we have not encountered in previous articles: superconductivity, particle polarization and quantum electronics.

If we look at these quantum technologies, imagine what it would be like to live in a world where quantum devices are everywhere. What would it mean to be technically literate if knowledge of quantum mechanics is a prerequisite for understanding everyday technology?

So pick up your binoculars, and let’s look at the quantum technologies that are coming over the next rand.

Superconductors

In a normal guidewire you can attach a battery and measure how fast the electrons move through it (the current, or number and velocity of electrons). It takes pressure (voltage) to push the electrons through, and when you push it, heat is released – think of the red glow of the coils in a room heater or hair dryer. The problem with pushing the electrons through a material is the resistance.

But we know that electrons move like waves. As you cool all the atoms in a material, the magnitude of the electron waves that carry the electric current increases. Once the temperature becomes low enough, this undulation can be of an annoying subtlety to the defining characteristic of the electrons. Suddenly the electron waves contract and move effortlessly through the material – the resistance drops to zero.

The temperature at which the wave of electrons takes over depends on the crystal in which the electrons are, but it is always cold, including temperatures at which gases such as nitrogen or helium become liquids. Despite the challenge of keeping things so cold, superconductivity is such an amazing and useful feature that we use it anyway.

Electromagnets. Most use of superconductivity is for the electromagnets in MRI (Magnetic Resonance Imaging) machines. As a child, you may have made an electromagnet by twisting a wire around a nail and attaching the wire to a battery. The magnet in an MRI machine is similar in that it is just a large wire roll. But if you have ~ 1000 amperes of current through the wire, the magnet will keep working duration. It normally looks like the world’s largest space heater.

So the answer is to use a special wire and cool it in liquid helium. Once it is superconducting, you can plug it into a power source and shoot up the current (it takes 2-3 days – there’s a great video to plug in an MRI magnet). Then pull out the magnet and walk away. Because there is no resistance, the current will continue to flow as long as you keep the magnet cold. When a hospital installs a new MRI, the magnet is turned on when it is installed, then the plug is pulled out and turned on for the rest of its life.

A superconducting magnet used for a particle detector.
Enlarge / A superconducting magnet used for a particle detector.

While MRI machines are the most visible examples, superconducting magnets are actually quite common. Any good chemistry lab or department has several superconducting magnets in their nuclear magnetic resonance (NMR) machines and mass spectrometers. Superconducting magnets lie 18 km from the Large Hadron Collider and they appear in other ways in physics sections. When we had a shoe project, we picked up a superconducting magnet from the storage track behind my lab and refurbished it. Physicists receive glossy catalogs by mail from superconducting magnet manufacturers.

Transmission lines. The next obvious application is to stretch a superconducting wire and use it to carry electricity. There are several demonstration projects around the world that use superconducting power lines. As with most industrial applications, it’s just a matter of finding cases where the performance of a superconductor is worth its high price. As prices fall, long-range superconducting transmission lines could be crucial, as we add more renewable solar and wind energy to the grid – being able to transmit long-distance powerlessly can eliminate local variations in renewable power production.

Generators and motors. If you have incredibly strong superconducting magnets, you want to use them in electric generators and motors. Cooling is as always a problem, but the much stronger magnets can make the car / generators significantly smaller and more efficient. It is particularly attractive for wind turbines (reduced weight on the tower) and electric drives for boats and aircraft (reduced weight and improved efficiency).

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