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arXiv:2205.09091 · Physical review. D/Physical review. D.

Astrometry in two-photon interferometry using an Earth rotation fringe scan

Zhi Chen, ANDREI NOMEROTSKI, Anže Slosar, Paul Stankus, Stephen Vintskevich

Published Jan 20, 2023• 13 citations
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Abstract

Optical interferometers may not require a phase-stable optical link between the stations if instead sources of quantum-mechanically entangled pairs could be provided to them, enabling long baselines. We developed a new variation of this idea, proposing that photons from two different astronomical sources could be interfered at two decoupled stations. Interference products can then be calculated in post-processing or requiring only a slow, classical connection between stations. In this work, we investigated practical feasibility of this approach. We developed a Bayesian analysis method for the earth rotation fringe scanning technique and showed that in the limit of high signal-to-noise ratio it reproduced the results from a simple Fisher matrix analysis. We identify candidate stair pairs in the northern hemisphere, where this technique could be applied. With two telescopes with an effective collecting area of $\ensuremath{\sim}2\text{ }\text{ }{\mathrm{m}}^{2}$, we could detect fringing and measure the astrometric separation of the sources at $\ensuremath{\sim}100\text{ }\text{ }\mathrm{\ensuremath{\mu}}\mathrm{as}$ precision in a few hours of observations, in agreement with previous estimates.

DOI
10.1103/physrevd.107.023015

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Optical interferometers may not require a phase-stable optical link between the stations if instead sources of quantum-mechanically entangled pairs could be provided to them, enabling long baselines. We developed a new variation of this idea, proposing that photons from two different astronomical sources could be interfered at two decoupled stations. Interference products can then be calculated in post-processing or requiring only a slow, classical connection between stations. In this work, we investigated practical feasibility of this approach. We developed a Bayesian analysis method for the earth rotation fringe scanning technique and showed that in the limit of high signal-to-noise ratio it reproduced the results from a simple Fisher matrix analysis. We identify candidate stair pairs in the northern hemisphere, where this technique could be applied. With two telescopes with an effective collecting area of \ensuremath∼2  m2\ensuremath{\sim}2\text{ }\text{ }{\mathrm{m}}^{2}\ensuremath∼2  m2, we could detect fringing and measure the astrometric separation of the sources at \ensuremath∼100  \ensuremathμas\ensuremath{\sim}100\text{ }\text{ }\mathrm{\ensuremath{\mu}}\mathrm{as}\ensuremath∼100  \ensuremathμas precision in a few hours of observations, in agreement with previous estimates.
Improved quantum sensing of photons from astronomical objects could provide high resolution observations in the optical benefiting numerous fields, including general relativity, dark matter studies, and cosmology. It has been recently proposed that stations in optical interferometers would not require a phase-stable optical link if instead sources of quantum-mechanically entangled pairs could be provided to them, potentially enabling hitherto prohibitively long baselines. A new refinement of this idea is developed, in which two photons from different sources are interfered at two separate and decoupled stations, requiring only a slow classical information link between them. We rigorously calculate the observables and contrast this new interferometric technique with the Hanbury Brown \& Twiss intensity interferometry. We argue this technique could allow robust high-precision measurements of the relative astrometry of the two sources. A basic calculation suggests that angular precision on the order of 101010 microarcseconds in the relative opening angle could be achieved in a single night's observation of two bright stars.
It has been recently suggested that optical interferometers may not require a phase-stable optical link between the stations if instead sources of quantum-mechanically entangled pairs could be provided to them, enabling extra- long baselines and benefiting numerous topics in astrophysics and cosmology. We developed a new variation of this idea, proposing that two photons from different sources could be interfered at two decoupled stations, requiring only a slow classical information link between them. We show that this approach could allow high- precision measurements of the relative astrometry of the two sources, with a basic calculation giving angular precision of 10 µas in a few hours’ observation of two bright stars. We also give requirements on the instrument for these observations, in particular on its temporal and spectral resolution. Finally, we discuss possible technologies for the instrument implementation and first proof-of-principle experiments.
Classical optical interferometry requires maintaining live, phase-stable links between telescope stations. This requirement greatly adds to the cost of extending to long baseline separations and limits on baselines will in turn limit the achievable angular resolution. Here we describe a novel type of two-photon interferometer for astrometry, which uses photons from two separate sky sources and does not require an optical link between stations. Such techniques may make large increases in interferometric baselines practical, even by orders of magnitude, with a corresponding improvement in astrometric precision benefiting numerous fields in astrophysics. We tested a benchtop analogue version of the two-source interferometer and unambiguously observe correlated behavior in detections of photon pairs from two thermal light sources, in agreement with theoretical predictions. This work opens new possibilities in future astronomical measurements.
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Astronomical observations allow us to better our understanding of the universe. As we observe smaller and more distance features, we run into the diffraction limit of our observation system. This limit is a function of the wavelength observed and the size of the primary aperture used. We can synthesize a larger primary aperture by implementing interferometry. Long baseline optical interferometry would lead to significant improvements in astronomical imaging resolution. Building optical interferometers with free space baselines becomes significantly more difficult as the baseline increases. A promising alternative is to use optical fiber to connect telescopes. Fiber-based interferometers are much more susceptible to phase noise than their free-space counterparts due to inhomogeneities in the fiber medium. This leads to significant degradation of interferometric signals used for astronomical measurements. We implement phase stabilization techniques used in quantum communications to stabilize an optical interferometer with a 170km pseudo-baseline. We use a quantum optimal measurement technique with this interferometer to resolve the extent of a source four times smaller than the diffraction limit of the system within 1.5% error. These results bring the potential for a full-scale on-sky long baseline interferometer significantly closer. A 350km baseline optical interferometer at 1550nm would allow us to resolve sub microarcsecond features in the universe.