Since the day Superconductors have been discovered, they have always turned heads, thanks to their distinctive properties. One such property of Superconductors is their ability to expel magnetic field lines, which leads to levitating phenomenons and makes them a hot topic of discussion in modern day world. Superconductivity is a quantum mechanical phenomenon, this is the reason that the levitation phenomenona associated with them is termed as Quantum Levitation.
What actually is levitation?
Going by the dictionary meaning, levitation refers to the action of rising or causing something to rise and hover in the air, typically by means of supposed magical powers.Levitation is accomplished by providing an upward force that counteracts the downward force ( like gravity ) plus a smaller stabilizing force that helps to keep the object at its home position. This force can be a fundamental force such as magnetic or electrostatic, or it can be any other reactive force.
How Quantum Levitation works?
Quantum Levitation employs the properties of quantum physics to levitate Superconductors over a magnetic source. We know that Superconductors don't like magnetic fields and hence they expel magnetic field lines whenever they are kept in magnetic field. This phenomena is termed as "Meisner's effect" and is only shown by type I Superconductors. However, there is also an another category of Superconductors, ie. Type II, which allow some of the magnetic field lines to pass through them and lead to a phenomena known as "Flux pinning", which is responsible for levitation processes.
Flux Pinning :When magnetic field is applied ,Superconducting currents develop on the surface in order to make a screen against this field. These currents are responsible for the Meissner effect. Other superconducting currents develop creating vortices (like non superconducting “tunnels”). These vortices allow a quantum of magnetic flux to go through them and thus enable part of the applied magnetic field to go through the superconducting sample. Because of these vortices, the superconductor becomes a sieve which enables part of the applied magnetic field to pass through. In this state, there is no resistance to electron flow, however the magnetic flux is pinned within these non-superconducting vortex areas, allowing the superconductive state to exist in much stronger magnetic field.
This pinning is what holds the superconductor in place thereby allowing it to levitate. This phenomenon is closely related to the Meissner effect, though with one crucial difference ,ie. the Meissner effect shields the superconductor from all magnetic fields causing repulsion, unlike the pinned state of the superconductor disk which pins flux, and the superconductor in place.
Where is it used?
On a simple 76 millimeter diameter, 1-micrometer thick disk, next to a magnetic field of 28 kA/m, there are approximately 100 billion flux tubes that can hold 70,000 times the superconductor's weight. These amazing numbers have made quantum levitation a hot topic of discussion in the modern world. There are already magnetic levitation trains in Asia which use this process, in addition to the more traditional electromagnetic levitation (maglev) trains.Another useful application includes the creation of truly frictionless bearings,lifts etc. Scientists are quite hopeful to employ this magical property of Superconductors for larger scale productive applications in near future by overcoming the present difficulties. Let's see what future surprises quantum levitation has in store for us!