How Superconductors Can Detect Gravitational Waves
Gravitational waves are vibrations in the fabric of spacetime. They are among the most exciting phenomena in the universe because they are generated by exotic processes such as collisions between black holes and even in the moment of creation itself, the Big Bang.
So finding a way to study them is a big deal for astronomers.
But there’s a problem. Gravitational waves squeeze and stretch space as they travel but their effects are tiny. Physicists calculate that the waves passing through Earth are changing the distance between London and New York by about the width of a uranium nucleus.
That makes them tough to spot, although he current generation of gravitational detectors ought to be able to detect this level of change (unless somebody’s got their numbers badly wrong).
Nevertheless, nobody has spotted a gravitational wave directly.
So a new way to find these beasts will surely be of interest. Today Armen Gulian at Chapman University in Maryland and a few pals outline a new type of detector that has the potential to be much smaller than today’s behemoths.
Conventional detectors are giant L-shaped interferometers with each arm being many hundreds of metres long. At the end of each arm is a mirror so a laser beam can bounce back and forth along the arms and then be made to interfere with itself.
Any change in the length of the arms ought to show up in any changes in the resultant interference pattern.
Gulian and co have a different idea. They imagine a bar of superconducting metal being hit by a gravitational wave. The waves act on all masses within the bar but the resulting movement of the metallic lattice, which is bound in place, will be very different from the movement of superconducting electrons, which are entirely unbound and free to move.
“Thus, the wave will tend to accelerate the electrons back and forth, towards and away from the ends of the bar,” they say.
Next, they place another superconducting bar at the end of the first but at right angles to it. While the first bar is squeezed by a gravitational wave, the second will be stretched. So the electrons in this bar will oscillate too, albeit shifted by half a period relative to the first.
Finally, if these bars are connected by a superconducting wire, an oscillating current should flow through it.
There are a few other subtleties to the design, largely to cope with the nature of superconductors, but this is essentially the principle they outline.
They go on to sketch the way a small such detector might work, made of bars just a few tens of centimetres long. A gravitational wave ought to generate a current of a few femtoamperes, a level that could be detectable with off-the shelf equipment.
Noise might be a problem, however. But Gulian and co say that if the frequency of the oscillations are known in advance much of the noise can be filtered out. In addition, the detector could be placed inside a magnetic bottle to screen out magnetic noise.
That’s an interesting idea which looks as if it could be considerably cheaper and simpler than the next generation of laser-based gear now being designed for future space missions such as LISA, (the laser interferometer space antenna). Worth looking at in more detail.
Ref: arxiv.org/abs/1111.2655: : Superconducting Antenna Concept for Gravitational Wave Radiation
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