B Can Phonon Excitations in BECs Revolutionize Gravitational Wave Detection?

[Auto-Didact]

Ivette Fuentes and her group are attempting to use phonon excitations in BECs to detect gravitational waves. Their GW-detector is called MAGA, which stands for Micrometre Antenna for Gravitational-wave Astronomy. Here's a video of her explaining it:



More from their blog:

MAGA is a proposed Gravitational Wave (GW) detector that uses the phononic excitations of a Bose-Einstein Condensate (BEC) to observe GWs. This revolutionary new type of detection scheme is underpinned by quantum field theory (QFT) in curved space‐time, a theory that has not been used before in GW physics. As the GW passes through the BEC, it resonates with a pre-prepared phononic quantum field, generating measurable changes to the state of this field. The signal is further enhanced by exploiting quantum correlations in the initial phononic field so that Quantum Metrology techniques can be applied. Unlike interferometry schemes that require a size of the order of kilometres, MAGA will be able to operate at similar levels of performance but with a size of the order of micrometres. This will enable small Earth‐based BEC setups that are of very low cost in comparison to interferometry-based detectors.

The type of GWs that should be detectable are those that would be expected from black hole and binary star merges, rotating neutron stars (with imperfections), and supernovae.

Currently MAGA is in the theoretical stage, with the characterization of all sources of noise being a primary target so that the detector can be designed appropriately for implementation in the laboratory. Information about realistic experimental capabilities will continue to be provided to our team by experimentalists L. Hackermüller (Nottingham), F. Cataliotti (INO‐CNR), C. Westbrook (CNSR) and J. Schmiedmayer (TU Vienna).

 

[Paul Colby]

One question I have because I have 0 details of the proposed detector physics is why is this a good approach? My naive thought is that very cold systems are dominated by few quantum states. If the energy required for the excitation to the first excited state is too great the probability of transition might tank (formal term for go to zero). Just asking.

 

[Auto-Didact]

One question I have because I have 0 details of the proposed detector physics is why is this a good approach? My naive thought is that very cold systems are dominated by few quantum states. If the energy required for the excitation to the first excited state is too great the probability of transition might tank (formal term for go to zero). Just asking.

Maybe http://maga-detector.weebly.com/theory.html on their blog can help with some of the detector physics. Else you could try reading a few of their papers, linked in this post.

In any case, I think the fact that it's an attempt to approach an experimental regime of general relativistic effects by using QT at relatively large scales (instead of GR at small scales), plays a big role. Optimistically, this might even kill two birds with one stone, namely detect Gravitational Waves and more importantly lead to experimental data in the ongoing quest to probe quantum gravity.

In other words: "We have no idea how to build it now, but it is not 10 orders of magnitude away."
Or, in this case: "We achieved the necessary temperature, the necessary number of atoms in the BEC, and the necessary lifetime individually, but achieving them at the same time will be very challenging - oh, and we have to put all this into some vibration-free environment, and we need this 1 million times or need a source that emits gravitational waves long enough for 1 million measurements".

An interesting approach, but I don't see this happening for quite some time.

Edit: Now discussed here

Challenging no doubt, but I can't help but still be somewhat excited though. It's not everyday you hear of a possibly doable experiment on the interface of QM and GR which isn't pretty much centuries or even millennia away, let alone already being undertaken. Unforeseen experimentally based directives pointing the way on the road towards quantum gravity are much needed and more than welcome.

Can you by the way give any estimates from experience how much you figure the cost of one of these detectors would end up being? I presume (naively) after a dozen or so replicated prototypes, scaling up to large amounts would be much more cost-efficient. And how challenging do you figure it, say compared to the prospects of building a larger collider (bigger than SSC) within the coming century?

 

[mfb]

I don't know how expensive such a detector would be.

How much would we learn from it? Let's say future improvements make it feasible, and such a detector is built. It picks up gravitational waves at the same time as LIGO/VIRGO or the Einstein telescope. And now? How does this improve the attempts to make a consistent theory of quantum gravity?
The experiment would test the weak field limit, where nonlinear effects are negligible. We know how to make quantum gravity in that regime. You can write down the Lagrangian, and it works perfectly well in first order - until you realize that the integrals in higher orders diverge for large energies.

We have experiments using a gravitational potential to get quantized energy levels already - neutrons bouncing above a surface for example.