Graduate Resolving power of a radio telescope array: Quantum or classical?

[Michael Price]

TL;DR

My question is: is the resolving power of an array of radio telescopes a quantum or a classical effect?

My question is: is the resolving power of an array of radio telescopes a quantum or a classical effect? The increase in resolving power of a single telescope, as aperture size increases, is easy to explain in terms of Heisenberg's uncertainty principle. But when we go an array of telescopes are told they "act together as one", but does that mean the signals from each telecope have to be coherently combined? Sometimes the signals are stored, prior to pooling, which suggests this is a classical effect.

One radio dish could process a single radio photon (in principle) to resolve its direction, but could an array of dishes resolve a single radio photon any more effectively?

 

[Andy Resnick]

But when we go an array of telescopes are told they "act together as one", but does that mean the signals from each telecope have to be coherently combined? Sometimes the signals are stored, prior to pooling, which suggests this is a classical effect.

Yes- Very Long Baseline Imaging (VLBI) imaging requires the signals be mutually coherent. Storing the digitized signals for later doesn't alter that- this is why the data requires extremely precise time-tagging in order to combine the digital data.

And yes- coherence is primarily a classical effect. There are quantum versions (the Hanbury Brown and Twiss effect is quantum), but VLBI uses plain ol' classical coherence.

 

[Michael Price]

Yes- Very Long Baseline Imaging (VLBI) imaging requires the signals be mutually coherent. Storing the digitized signals for later doesn't alter that- this is why the data requires extremely precise time-tagging in order to combine the digital data.

Thanks. Does that mean the source must be varying for this to work? Or is the variation required so small that is never a problem?

 

[Andy Resnick]

Thanks. Does that mean the source must be varying for this to work? Or is the variation required so small that is never a problem?

What source do you mean?

 

[Michael Price]

What source do you mean?

I mean the source (star, galaxy,...) we are trying to resolve.

 

[DaveE]

Thanks. Does that mean the source must be varying for this to work? Or is the variation required so small that is never a problem?

No. It just means that the signals from the different antennas must be synchronized in time to an accuracy that allows for recombination coherently (i.e. a small fraction of a wavelength). This allows for interference effects from the phase of the waves observed in addition to the amplitude. So, when observations are recorded, they are "time stamped" with extreme accuracy.

 

[Michael Price]

No. It just means that the signals from the different antennas must be synchronized in time to an accuracy that allows for recombination coherently (i.e. a small fraction of a wavelength). This allows for interference effects from the phase of the waves observed in addition to the amplitude. So, when observations are recorded, they are "time stamped" with extreme accuracy.

Thanks. And that nicely explains why it is easier with radio telescopes than optical ones.

 

[Andy Resnick]

I mean the source (star, galaxy,...) we are trying to resolve.

Yes.