Using atomic clocks for gravitational wave detection

[Chronos]

This paper, http://arxiv.org/abs/1501.00996, proposes using atomic clocks for gravitational wave detection. It sounds similar to other ideas involving pulsar timing experiments. The twist here is utilizing satellites to provide a wide base for improved sensitivity. Sounds like an inexpensive alternative to LIGO.

 

[Matterwave]

I'd like to see some plots comparing this proposed scheme's sensitivity and frequency range to those of eLISA (since those are the sources this paper seems to be claiming to also look at). Are they comparable?

But if this new proposal is looking to be similar to eLISA, it would suggest that this scheme is not really an alternative to advanced LIGO since advanced LIGO scans a different set of frequency ranges which correspond to different sources (usually merging binary neutron stars or stellar mass black holes in nearby galaxies rather than merging supermassive black holes in distant galaxies as is talked about here).

 

[Chronos]

I queried Professor Moaz about the possibility of using this approach to detect gravitational waves from inflation. He replied it was, in principle, but, they would be more difficult to detect than those from SMBH, etc. A reference was included: http://www.tapir.caltech.edu/~teviet/Waves/gwave_spectrum.html

 

[Matterwave]

Do you know where this new atomic clock GW detector's sensitivity curve would lie on that plot? Would it be roughly where eLISA is?

I notice this plot has LISA instead of eLISA, was it perhaps made before the new spec changes made due to NASA abandoning the LISA project?

 

[Chronos]

Per the paper, the baseline distance for eLISA will be 10E06 km with a sensitivity at .1 - 100mHz. The configuration for the atomic clock proposal would have an 8.3 light minutes, or 10E08 km baseline. Assuming sensitivity is linear wrt baseline distance, it naively appears it should be in the 10 to 10000 mHz range.

 

[Matterwave]

Are u sure the frequency ranges have a proportional dependence on the length of the arms? (Rather than inverse proportionality?) Because eLISA has MUCH longer arms than LIGO but it is scanning a frequency range that is much SMALLER than that of LIGO not larger.

 

[Chronos]

No, I'm not at all sure. Signal sensitivity is not necessarily related to measurement sensitivity.

 

[Matterwave]

It would be nice if the authors could provide a plot of the sensitivity and ranges as is standard...

 

[mfb]

Frequency range is one over distance (modified with some function depending on the details of the detector). That is the main argument for space-based detectors: you get in the frequency range of orbiting bodies. eLISA has a sensitivity in the range of 1 mHz to 1 Hz (plot), that would give this approach access to 0.01 to 10 mHz, or cycle times of three hours to a minute. This is well in agreement with the 8 light-minutes of separation, as expected. They seem to be a bit more conservative, limiting the frequency range to < 1 mHz to avoid having more than half a wavelength between the spacecrafts.

A very interesting approach. Cheaper? We'll have to see. You still have to measure the arrival times of light signals with an uncertainty significantly below the frequency of the light (and they propose an interferometer...). I would expect you still need the extremely drag-free test masses to keep control of the expected path over the timescale of hours. The proposed 10 kW laser is massive. They compare the power requirement to the ISS!

I think the idea is too new for sensitivity estimates, those will need a more detailed design.

 

[dougfgd]

I recall that gamma wavelengths are shorter giving higher resolution.
Though not coherent gamma emitted by radioactive crystalline materials can detect very small velocity changes between emitter and absorber (mossbauer)http://www.rsc.org/membership/networking/interestgroups/mossbauerspect/intropart1.asp
Does a coherent gamma source exist ? could it be flown?