Radio VLBI and the quantum interference paradox

TL;DR

This paper investigates whether the routine recording and correlation of signals in radio VLBI experiments violate quantum interference principles, providing a resolution to this apparent paradox.

Contribution

It offers a theoretical explanation reconciling radio VLBI practices with quantum interference principles, addressing a longstanding paradox.

Findings

Radio VLBI does not violate quantum interference principles.

Recording signals separately and correlating offline is consistent with quantum mechanics.

The paradox is resolved through a detailed quantum analysis of the measurement process.

Abstract

We address here the question of interference of radio signals from astronomical sources like distant quasars, in a very long baseline interferometer (VLBI), where two (or more) distantly located radio telescopes (apertures), receive simultaneous signal from the sky. In an equivalent optical two-slit experiment, it is generally argued that for the photons involved in the interference pattern on the screen, it is not possible, even in principle, to know which of the two slits a particular photon went through and that any procedure to ascertain this destroys the interference pattern. But in the case of the modern radio VLBI, it is a routine matter to record the phase and amplitude of the voltage outputs from the two radio antennas on a recording media separately and then do the correlation between the two recorded signals later in an offline manner. Does this not violate the quantum interference principle? We provide a resolution of this problem here.