Three articles report on the recent paper in Phys Rev. D: Flanagan, Éanna É. et al. 2019 Persistent gravitational wave observables: General framework (also ArXiv):
- Phys.org: Gravitational waves leave a detectable mark, physicists say
- APS: Synopsis: Persistence of Gravitational-Wave Memory
- Live Science: The Universe Probably 'Remembers' Every Single Gravitational Wave
The Live Science article's summary is probably the most simplified. One of the three new proposed effects is explained as follows:
Two atomic clocks placed some distance from each other would experience a gravitational wave differently, including its time-dilation effects: Because time would be slowed more for one clock than the other, subtle differences in their readings after a wave passed might reveal a memory of the wave in the local universe.
Question: Could two atomic clocks really be used to detect gravitational waves from a distant source? If so, how in principle?
I'm not asking if a practical detector could be built today using two atomic clocks. I'm just asking how two atomic clock could do this in principle, as (apparently) Flanagan et al. seem to suggest.
The three effects described in Flanagan et al. are summarized in the Phys.org article as follows:
The researchers identified three observables that show the effects of gravitational waves in a flat region in spacetime that experiences a burst of gravitational waves, after which it returns again to being a flat region. The first observable, "curve deviation," is how much two accelerating observers separate from one another, compared to how observers with the same accelerations would separate from one another in a flat space undisturbed by a gravitational wave.
The second observable, "holonomy," is obtained by transporting information about the linear and angular momentum of a particle along two different curves through the gravitational waves, and comparing the two different results.
The third looks at how gravitational waves affect the relative displacement of two particles when one of the particles has an intrinsic spin.