A Curious Observer’s Guide to Quantum Mechanics, Volume 7: The Quantum Age

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

As tool builders, we have only recently been able to use quantum mechanics. Understanding and manipulating quantum devices is 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 encountered some of these quantum technologies in the previous articles. 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 at a near future where quantum technologies are likely to permeate our daily existence. You don’t have to look far – all the technologies we research today already exist. Most are still rare, isolated in laboratories or as demonstration models of technology. 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 take a look at some of the technologies we didn’t encounter in previous articles: superconductivity, particle polarization, and quantum electronics.

When we look at these quantum technologies, 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 connect a battery and measure how fast the electrons move through it (the current, or the number and speed of electrons). It takes some pressure (voltage) to push the electrons through, and that releases some heat – think of the red glow of the coils in a room heater or a hairdryer. The difficulty of pushing the electrons through a material is the resistance

But we know that electrons move like waves. When you cool all the atoms in a material, the magnitude of the electron waves that carry the electric current increases. Once the temperature gets low enough, this undulation can turn from an annoying subtlety to the defining property of the electrons. Suddenly the electron waves form pairs 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 in which the electrons are located, but it is always cold, with temperatures at which gases such as nitrogen or helium liquefy. Despite the challenge of keeping things so cold, superconductivity is such a great 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 just a large coil of wire. But if ~ 1000 Amps of current flows through the wire, keeping the magnet going will get to work expensiveIt 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 crank it up (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. Because there is no resistance, the current continues 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.

While MRI machines are the most visible examples, superconducting magnets are actually quite common. Any good chemistry lab or department will have several superconducting magnets in their nuclear magnetic resonance (NMR) machines and mass spectrometers. Superconducting magnets line 18 km from the Large Hadron Collider, and they show up on physics departments in other ways. When we had a small project, we scraped a superconducting magnet from the storage aisle behind my lab and renovated it. Physicists receive glossy catalogs from superconducting magnet manufacturers.

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 is a matter of finding cases where the performance of a superconductor is worth its cost. As the price falls, long-distance superconducting transmission lines could become crucial as we add more renewable solar and wind power to the grid. The ability to transmit power over long distances without loss can even compensate for local variations in renewable energy production.

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