A curious guide for the quantum mechanics observer, point 7: The quantum century

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

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

We found some of these quantum technologies in the previous articles. Some of them, like quantum dots on TVs, are already becoming common; others, like optical clocks, exist, but are still very rare.

As this is the last article in this series, I would like to look to the near future, where quantum technologies are likely to infuse into our everyday existence. There is no need to go very far – all the technologies that we will explore today already exist. Many of them are still rare, isolated in laboratories or as demonstrators of technology. Others are hidden from view, like the MRI machine at the local hospital or the hard drive on your desk. In this article, we will focus on some of the technologies that we did not find in previous articles: superconductivity, particle polarization and quantum electronics.

As we look at these quantum technologies, imagine what it will be like to live in a world where quantum devices are everywhere. What will it mean to be technically literate when knowing quantum mechanics is a prerequisite for understanding everyday technology?

So, grab your binoculars and see quantum technologies reaching the next summit.

Superconductors

On a normal wire, you can connect a battery and measure how quickly electrons move through it (the current or number and speed of electrons). It takes a little pressure (voltage) to push the electrons, and in doing so, the push releases some heat – think of the red glow of the spirals in a heater or hair dryer. The difficulty of pushing 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 size of the electron waves that carry the electric current increases. Once the temperature gets low enough, this ripple can pass from an annoying subtlety to an electron defining characteristic. Suddenly, electron waves pair and move effortlessly through the material – the resistance drops to zero.

The temperature at which the electron ripple takes place depends on the crystal the electrons are in, but it is always cold, involving temperatures in which gases such as nitrogen or helium become liquid. Despite the challenge of keeping things that cold, superconductivity is such an incredible and useful property that we are using it anyway.

Electromagnets. The most widespread use of superconductivity is for electromagnets in MRI (Magnetic Resonance Imaging) 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 when you have ~ 1000 Amps of current flowing through the wire, keeping the magnet running becomes expensive. It would normally end up looking like the biggest space heater in the world.

So the answer is to use a special wire and cool it in liquid helium. When you are superconducting, you can connect it to a power source and increase the current (this takes 2 to 3 days – there is a great video of connecting an MRI magnet). Then you disconnect the magnet and go 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 is turned on when it is installed, then it is disconnected and left on for the rest of its life.

Although MRI machines are the most visible examples, superconducting magnets are quite common. Any good laboratory or chemistry department will have 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 other ways in the physics departments. When we had a tight project, we took a superconducting magnet from the storage alley behind my lab and renovated it. Physicists receive glossy catalogs 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 is just a matter of finding cases where the performance of a superconductor is worth its high price. As the price drops, superconducting long-distance transmission lines can become crucial as we add more renewable solar and wind energy to the grid – the ability to send lossless energy over long distances can balance local variations in renewable energy production.

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