Mon. Sep 26th, 2022
A Curious Observer's Guide to Quantum Mechanics, Part 7: The Quantum Age

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One of the quietest revolutions of our present century is the entry of quantum mechanics into our everyday technology. Quantum effects used to be limited to physics labs and delicate experiments. But modern technology increasingly relies on quantum mechanics for its basic operation, and the importance of quantum effects will only increase in the coming decades. As such, physicist Miguel F. Morales has taken on the mammoth task of explaining quantum mechanics to laymen in this seven-part series (no math, 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 very evenly distributed –William Gibson

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

In the previous articles, we came across some of these quantum technologies. Some of them, like the quantum dots in TVs, are already becoming commonplace; others, such as optical clocks, exist but are still very rare.

Since this is the last article in this series, I’d like to look to a near future where quantum technologies are likely to infuse our day-to-day existence. You don’t have to look far: all the technologies we’re going to explore today already exist. Most are still rare, isolated in labs or as technology demonstrators. Others hide in plain sight, such as the MRI machine at the local hospital or the hard drive on your desk. In this article, let’s focus on some of the technologies we haven’t encountered in previous articles: superconductivity, particle polarization, and quantum electronics.

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

So grab your binoculars, and let’s take a look at the quantum technologies coming over the next ridge.

superconductors

In a normally conductive wire you can attach a battery and measure how fast the electrons pass through it (the current, or the number and speed of electrons). It takes some pressure (tension) to push the electrons through, and doing so releases some heat — think of the red glow from the coils in a room heater or hair dryer. The difficulty in pushing the electrons through a material is the resistance

But we know that electrons move like waves. As you cool down all the atoms in a material, the electron waves that carry the electric current get bigger. Once the temperature gets low enough, this undulation can change from an annoying subtlety to the defining characteristic of the electrons. Suddenly the electron waves form a pair and move effortlessly through the material – the resistance drops to zero.

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

Electromagnets. The most widespread use of superconductivity is for the electromagnets in magnetic resonance imaging (MRI) machines. As a child, you may have made an electromagnet by wrapping a wire around a nail and attaching the wire to a battery. The magnet in an MRI machine is similar in that it is simply a large coil of wire. But if ~1000 amps of current flow through the wire, it will keep the magnet working expensive† It would normally look like the world’s largest space heater.

So the answer is to use a special wire and cool it in liquid helium. Once it’s superconducting, you can plug it into a power source and increase the current (this will take 2-3 days – there’s a great video on how to hook up an MRI magnet). Then disconnect the magnet and walk away. Since 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 turns on when it’s installed, then unplugged and left 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. Every good chemistry lab or department has several superconducting magnets in their Nuclear Magnetic Resonance (NMR) machines and mass spectrometers. Superconducting magnets line 18 km of the Large Hadron Collider and appear in physics departments in other ways. When we had a small project, we took a superconducting magnet from the storage area behind my lab and renovated it. Physicists receive glossy catalogs in the mail from manufacturers of superconducting magnets.

Transmission lines. The next obvious application is to stretch a superconducting wire and use it to transport 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 a superconductor’s performance is worth its high price. As the price falls, long-distance superconducting transmission lines could become crucial as we add more renewable solar and wind energy to the grid – the ability to carry power over long distances without loss could offset local variations in renewable energy production.

Generators and engines. If you have incredibly strong superconducting magnets, you’ll want to use them in electrical generators and motors. Cooling is an issue as always, but the much stronger magnets can make the motor/generators significantly smaller and more efficient. This is especially attractive for wind turbines (reduced weight on the tower) and electric drives for boats and aircraft (reduced weight and improved efficiency).

By akfire1

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