How to turn the vacuum into a superconductor
* 08 April 2011 by Maggie McKee
* Magazine issue 2807. Subscribe and save
TURNING a vacuum into a superconductor could be as simple as zapping it with a super-powerful magnet.
That's according to Maxim Chernodub of the University of Tours in France, who believes powerful magnetic fields could pluck charged particles out of the vacuum of space and set them flowing as a current that never encounters any resistance.
This seemingly bizarre proposal is a consequence of the uncertainty principle of quantum theory, which says we can never be sure that a vacuum is truly empty. Instead, space is fizzing with "virtual" particles, which tend to disappear almost as soon as they form. In principle, however, they could stick around long enough to become real, if they could avoid adding energy to the universe's current tally - in accordance with the law of conservation of energy.
That's exactly what happens when charged particles that behave like tiny bar magnets pop out of the vacuum in a strong magnetic field. The particles rotate so their internal magnetic field aligns with the external one, which decreases the total energy. If the field is strong enough, the virtual particles can become real. "You can add many particles with no cost of energy," says Chernodub. Such particles all share the same quantum state and form what is known as a condensate, in which they flow together as one and carry current without resistance.
Previous research had focused on relatively heavy particles, called W bosons, that pop out of the vacuum in this way. But Chernodub modelled the scenario with lighter particles called rho mesons, which require less powerful magnetic fields to become real.
Chernodub calculates that when the magnetic field reaches 1016 Tesla, condensates of rho mesons should appear from the vacuum. The work is due to be published in Physical Review Letters.
Chernodub likens the resulting condensate to that formed by ordinary superconductors. Below a certain critical temperature, electrons in these materials bind together in so-called Cooper pairs, which all share the same quantum state and so flow without friction. However, Paul Olesen of the University of Copenhagen in Denmark says the similarity is not exact because ordinary superconductors repel magnetic fields.
Could the vacuum of space be harnessed to create ultra-efficient electricity? Nice idea, says Dmitri Kharzeev of Brookhaven National Laboratory in Upton, New York, but it won't be happening any time soon. The required magnetic field dwarfs even the most magnetic things in the universe today - neutron stars called magnetars, which boast fields of up to 1011 Tesla.
"If Earth's magnetic field were 17 orders of magnitude stronger than it is now, and you could generate energy on a space station in some way, then you would be able to transport current from space to Earth along the lines of magnetic field," says Kharzeev. "We would not need power supply lines, we could transfer current over empty space."
Magnetic fields of the required strength might have existed in the early universe. If that led to superconductivity, then the currents produced might have had some effect on cosmic structure, says Kharzeev. But he adds that the high temperatures at the time may have destroyed the effect.
Today, such magnetic fields might appear fleetingly in Brookhaven's Relativistic Heavy Ion Collider or at the Large Hadron Collider near Geneva, Switzerland. Researchers now plan to search their data for hints of the phenomenon.
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