This Month in Science: Quantum Levitation

Quantum levitation isn’t a phrase you hear every day, but it is an interesting physical phenomenon that, at first glance, looks like magic. Quantum levitation is possible because of some unique atomic properties that occur when a superconducting object interacts with a very strong magnet1. The interaction allows the object to float above the magnet. Although the technology hasn’t advanced to this point yet, quantum levitation could one day be used to levitate very heavy objects, like cars or trains2.

Superconductors can be understood in the context of a normal conductor. A conductor is a material, like copper, that allows an electrical current to pass through it3. Negatively charged electrons travel through a conductor and produce an electrical current. In a normal conductor, these electrons bump into the atoms that form the conductor losing energy with each collision. This energy loss is called resistance. The energy lost generates heat and causes the conductor to heat up.

Some normal conducting materials become superconductors when cooled to a sufficiently low temperature, called the critical temperature. When the object is superconducting, there is no resistance to electrical current. No resistance means that electrons travel through the object material without losing any energy4.

When elements combine to form compounds such as alloys and ceramics, superconducting can occur at what are considered to be “high” temperatures: -315°F (-193°C)4. While this might not seem very warm, it allows materials to be cooled when submerged in liquid nitrogen3. Quantum levitation occurs when an object—such as the disc pictured above—is cooled to the superconducting state and placed over a strong magnet. If the temperature rises above the critical temperature, the object is no longer in the superconducting state and will fall.

The superconducting object floats because it avoids the magnetic field produced by the magnet. In a normal conductive state, a magnetic field will pass directly through the conductor. In a superconducting state, the object experiences the Meissner effect. The Meissner effect states that a magnetic field does not penetrate a superconducting material because it is actively expelled from the object5. This effect was discovered in 1933 by German physicists Dr. Walther Meissner and Dr. Robert Ochsenfeld6.

While the Meissner effect causes the object to push away from the magnet, it is not responsible for holding the object in place. It is the combination of the Meissner effect and flux tubes that is responsible for “locking” the object above the magnet. Flux tubes are tiny channels that exist in certain types of superconducting materials. Instead of being fully expelled, the magnetic field is allowed to pass through these tiny channels within the object, pinning it in place1. Known as flux pinning, the effect is so strong, it can hold the object in place above a magnet at an angle, looking as though it’s defying gravity.

While superconductors as a material have many applications, the current applications of quantum levitation are limited. Superconductors are used to increase the speed of connection in computer chips and make imaging using MRI machines possible7. Superconducting magnets are used in Japan and Germany for magnetic levitation (maglev) trains. In principle, quantum levitation can also be used to levitate very heavy objects. If the technology can be scaled up to larger objects, quantum levitation could be an alternative to maglev trains or even used to levitate cars in the future2. Can you think of any other potential applications? To see quantum levitation in action, check out this video of a demonstration based on research at Tel-Aviv University8. You can also see quantum levitation during special events at Cape Fear Museum.



Previous Columns

March 2019: Venus Flytrap
February 2019: A Shifting Magnetic Field
January 2019: Giant Ground Sloth
December: Snowflakes
November: Citizen Science
October: Parker Solar Probe Voyaging to the Sun
August: Sea Turtle Season
July: Plastic Free July
June 2018: All About Alligators

A superconducting disc levitates above a magnetic track.

This is an illustration of the Meissner effect. It shows a magnetic field bending around a material in a superconductive state instead of passing through like it would in the normal conductive state.
Credit: Piotr Jaworski

An illustration of magnetic field lines passing through flux tubes in a superconducting disc.
Credit: iO9
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