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arXiv:2403.03491 · New Journal of Physics

Practical approach to extending baselines of telescopes using continuous-variable quantum information

Bran Purvis, Randy Lafler, R Nicholas Lanning

Published Sep 20, 2024• 3 citations
arXivHTMLPDF

Abstract

Abstract Interferometric telescopes are instrumental for the imaging of distant astronomical bodies, but optical loss heavily restricts how far telescopes in an array can be placed from one another, leading to a bottleneck in the resolution that can be achieved. An entanglement-assisted approach to this problem has been proposed by (Gottesman et al 2011 Phys. Rev. Lett. 109 070503), as a possible solution to the issue of optical loss if the entangled state can be distributed across long distances by employing a quantum repeater network. In this paper, we propose an alternative entanglement-assisted scheme that interferes a two-mode squeezed vacuum state with the astronomical state and then measures the resulting state by means of homodyne detection. We use a continuous-variable approach and compute the Fisher information with respect to the mutual coherence of the astronomical source. We show that when the Fisher information is observed cumulatively at the rate at which successful measurements can be performed, our proposed scheme does not outperform the traditional direct detection approach or the entanglement-assisted approach of GJC12.

DOI
10.1088/1367-2630/ad7dab

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Abstract Interferometric telescopes are instrumental for the imaging of distant astronomical bodies, but optical loss heavily restricts how far telescopes in an array can be placed from one another, leading to a bottleneck in the resolution that can be achieved. An entanglement-assisted approach to this problem has been proposed by (Gottesman et al 2011 Phys. Rev. Lett. 109 070503), as a possible solution to the issue of optical loss if the entangled state can be distributed across long distances by employing a quantum repeater network. In this paper, we propose an alternative entanglement-assisted scheme that interferes a two-mode squeezed vacuum state with the astronomical state and then measures the resulting state by means of homodyne detection. We use a continuous-variable approach and compute the Fisher information with respect to the mutual coherence of the astronomical source. We show that when the Fisher information is observed cumulatively at the rate at which successful measurements can be performed, our proposed scheme does not outperform the traditional direct detection approach or the entanglement-assisted approach of GJC12.
We propose a method to build an astronomical interferometer using continuous-variable quantum teleportation to overcome transmission loss between distant telescopes. The scheme relies on two-mode squeezed states shared by distant telescopes as entanglement resources, which are distributed using continuous-variable quantum repeaters. We find the optimal measurement on the teleported states, which uses beam splitters and photon-number-resolved detection. Compared to prior proposals relying on discrete states, our scheme has the advantages of using linear optics to implement it without wasting stellar photons, and making use of multiphoton events, which are regarded as noise in previous discrete schemes. We also outline the parameter regimes in which our scheme outperforms the direct detection method, schemes utilizing distributed discrete-variable entangled states, and local heterodyne techniques.
It has been shown that shared entanglement between two telescope sites can in principle be used to localize a point source by mimicking the standard phase-scanning interferometer, but without physically bringing the light from the distant telescopes together. In this paper, we show that a receiver that employs spatial-mode sorting at each telescope site, combined with pre-shared entanglement and local quantum operations can be used to mimic the most general multimode interferometer acting on light collected from the telescopes. As an example application to a quantitative passive-imaging problem, we show that the quantum-limited precision of estimating the angular separation between two stars can be attained by an instantiation of the aforesaid entanglement based receiver. We discuss how this entanglement assisted strategy can be used to achieve the quantum-limited precision of any complex quantitative imaging task involving any number of telescopes. We provide a blueprint of this general receiver that involves quantum transduction of starlight into quantum memory banks and spatial mode sorters deployed at each telescope site, and measurements that include optical detection as well as qubit gates and measurements on the quantum memories. We discuss the relative Fisher-information contributions of local mode sorting at telescope sites vis-a-vis distributed entanglement-assisted interferometry, to the overall quantum-limited information about the scene, based on the ratio of the baseline distance to the individual telescope diameter.
A quantum-enhanced telescope (interferometer) can have significant advantages in precisely measuring the angular position of remote objects through sending out ancillary quantum entanglement pairs alongside the large baselines of telescopes. In principle, the larger the baseline, the higher the expected measurement resolution. However, the well-known major problem of photon transmission loss would drastically undermine the practical application of all quantum-enhanced telescopes and optical interferometers that transmit photons along the baseline, especially for the large baselines required for high angular resolution. Here, we propose a photon-transmission-loss-independent quantum-enhanced interferometer that is robust to the transmission loss and keeps its advantages unchanged given whatever large baseline. This removes the well-known barrier to the practical application of quantum-enhanced telescopes. Moreover, in contrast to the previous results of quantum-entanglement-enhanced telescopes requesting sophisticated resources—perfect single-photon entanglement, photon-number-resolving detectors, or quantum memories—our method requires only threshold detectors and tunable coherent-state or two-mode squeezed-state sources, which are mature technologies nowadays, and it does not need any quantum memory. We demonstrate the high performance of our method using Fisher information. For the phase difference of weak light from a remote star, the high-quality result of Fisher information remains constant under arbitrarily large transmission loss, and hence all the advantageous results and the performance of our method are actually independent of transmission loss.
Telescope systems with distributed apertures are a well-established approach for boosting resolution in astronomical imaging. However, theoretical limits on quantitative imaging precision, and the fundamentally best possible mode-sorting, beam-combining, and detection schemes to use with such arrays, remain largely unexplored. Using mathematical tools of the quantum and classical Crámer-Rao bounds, we perform analyses showing the fundamental origins of the enhancement provided by distributed imaging systems, over and above a single monolithic telescope, and consider the precision with which one can estimate any desired parameter embedded in a scene's incoherent radiation with a multi-aperture imaging system. We show how quantum-optimal measurements can be realized via beam-combination strategies of two classes: (1) , where light from different apertures is directed to a common focal plane, e.g., of a segmented-aperture telescope; and (2) , where light collected at each aperture, e.g., telescope sites of a long-baseline array, is routed to an optical interferometer. As an example, we show an explicit calculation of the quantum Fisher information (QFI) for estimating the angular separation between two-point emitters using two identical apertures separated by a baseline distance. We show that this QFI splits instructively into additive contributions from the single apertures and from the baseline. We quantify the relative benefits of intratelescope (e.g., spatial-mode) optical processing and intertelescope beam combination. We show how both receiver designs can be used to capture both sources of information and discuss how similar methods could be extended to more general imaging tasks. We discuss translating QFI-attaining measurements to explicit receiver designs, and the use of preshared entanglement to achieve the QFI when it is impractical to colocate and combine light collected by the apertures. Published by the American Physical Society 2024
In optical and IR wavelengths, typical astronomical sources have only one or a few photons arriving at a time, meaning the light is really a quantum object. This makes interferometry over longer baselines a major challenge, requiring a truly quantum interference measurement between distant elements in the array rather than local measurements which can be combined later. Luckily, our ability to manipulate and preserve quantum states has taken major strides forward in the last few decades with the rise of quantum information technologies. I will explain how entangled quantum states and a technology called "quantum repeaters" can make possible telescope arrays with much longer baselines than existing facilities, and discuss progress towards making such quantum telescopes a reality.