[ExI] A new type of gravitational waves detector

[John Clark]

A new type of very compact gravitational wave detector has been proposed
that's really cool, it would work in theory but would be very tricky to
make. But If we can figure out how to engineer it a detector just 1 meter
long would be as sensitive as the 4000 meter long LIGO detector; in fact it
would be so sensitive it could detect the Frame Dragging which Einstein
predicted the rotation of the earth would produce, and that's something
even LIGO can't do. The idea is to take an artificial diamond of one 1/1000
of a millimeter across and put it into a quantum superposition, such an
object is very small by human standards but it's large enough to be seen
with a regular optical microscope, and that is enormous for the quantum
world.

The diamond would be absolutely perfect except for one flaw, one carbon
atom in the lattice would be replaced by a single nitrogen atom. A
microwave photon would then hit the nitrogen atom which, according to the
weird laws of quantum mechanics, would both absorb and not absorb the
photon. The nitrogen atom that absorbs the photon would jump into a "spin
one state" and develop a magnetic field as a result, the atom that didn't
absorb the photon would remain in a "spin zero state" and have no
magnetism. Then by applying an external magnetic field it would be possible
to separate the two atoms and the carbon lattices they are attached to by a
distance as far as 1 meter. The external magnetic field would then be
reversed which would bring the two superpositions back together again.

The last step is to send another microwave photon at the nitrogen atom, it
would be carefully tuned to change the shape of the superposition so that
the crests and troughs of the spin-one state perfectly overlap and cancel
out, while the crests of the spin-zero state overlap and reinforce each
other. Thus, in the absence of outside interference at the end of all this
a measurement of the electron would always find it in a spin-zero state.
That is to say if no gravitational waves occurred at the time of separation
the nitrogen atom will always be in the spin zero stay but if a
gravitational wave occurred during the separation things would no longer
perfectly overlap and a magnetic spin one state would be detected in the
resulting data with the frequency of the gravitational wave.

Although most of these steps have already been performed in the lab, or
something close to it (recently a superposition of 10,000 atoms over a
distance of half a meter has been achieved, but this micro diamond would
contain about 10 billion atoms), nobody has ever done all these steps at
the same time so it won't be easy. As one scientist put it, it's one thing
to learn how to ride a bicycle and juggle, it's quite another to learn how
to ride a bicycle while you're juggling. But if we can figure out how to do
this it would be amazing, as Sougato Bosem the lead researcher on the
project said "*The challenge is to get one of them working. If one of them
works, it would be very easy to make several more*".

Mesoscopic Interference for Metric and Curvature (MIMAC) & Gravitational
Wave Detection <https://arxiv.org/pdf/1807.10830.pdf>

John K Clark
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