Modern optics focuses on photonics and quantum optics, studying individual photons and statistics of photon streams. Those can be complex and carry information beyond that recorded by imaging, spectroscopy, polarimetry or interferometry. Since [almost] all astronomy is based upon the interpretation of subtleties in the light from astronomical sources, quantum optics has the potential of becoming another information channel from the Universe. The observability of quantum statistics increases rapidly with telescope size making photonic astronomy very timely in an era of very large telescopes.
Modern optics focuses on photonics and quantum optics, studying individual photons and statistics of photon streams. Those can be complex and carry information beyond that recorded by imaging, spectroscopy, polarimetry or interferometry. Since [almost] all astronomy is based upon the interpretation of subtleties in the light from astronomical sources, quantum optics has the potential of becoming another information channel from the Universe. The observability of quantum statistics increases rapidly with telescope size making photonic astronomy very timely in an era of very large telescopes.
Abstract Quantum optics potentially offers an information channel from the Uni-verse beyond the established ones of imaging and spectroscopy. All existing cam-eras and all spectrometers measure aspects of the first-order spatial and/or temporal coherence of light. However, light has additional degrees of freedom, manifest in the statistics of photon arrival times, or in the amount of photon orbital angular mo-mentum. Such quantum-optical measures may carry information on how the light was created at the source, and whether it reached the observer directly or via some intermediate process. Astronomical quantum optics may help to clarify emission processes in natural laser sources and in the environments of compact objects, while high-speed photon-counting with digital signal handling enables multi-element and long-baseline versions of the intensity interferometer. Time resolutions of nanosec-onds are required, as are large photon fluxes, making photonic astronomy very timely in an era of large telescopes. 1 What Is Observed in Astronomy? Almost all of astronomy depends on the interpretation of properties of electromag-netic radiation (“light”) from celestial sources. The sole exceptions are neutrino detections; gravitational-wave searches; analyses of cosmic rays, meteorites, and other extraterrestrial materials; and in-situ studies of solar-system bodies. All our other understanding of the Universe rests upon observing and interpreting more or less subtle properties in the light reaching us from celestial bodies. Astronomical telescopes are equipped with myriads of auxiliary instruments which, on first sight, may give an impression of being vastly different. However, a closer examination of the underlying physical principles reveals that they all are measuring either the spatial or temporal [first-order] coherence of light (or perhaps some combination of these). All imaging devices (cameras, interferometers) are studying aspects of the spatial coherence (in various directions, and for different angular extents on the sky). All spectrally analyzing devices measure aspects of the
Astrophotonics is a burgeoning field that lies at the interface of photonics and modern astronomical instrumentation. Here we provide a pedagogical review of basic photonic functions that enable modern instruments, and give an overview of recent and future applications. Traditionally, optical fibres have been used in innovative ways to vastly increase the multiplex advantage of an astronomical instrument, e.g. the ability to observe hundreds or thousands of stars simultaneously. But modern instruments are using many new photonic functions, some emerging from the telecom industry, and others specific to the demands of adaptive optics systems on modern telescopes. As telescopes continue to increase in size, we look to a future where instruments exploit the properties of individual photons. In particular, we envisage telescopes and interferometers that build on international developments in quantum networks, the so-called quantum internet. With the aid of entangled photons and quantum logic gates, the new infrastructures seek to preserve the photonic state and timing of individual photons over a coherent network.
Classically, the angular resolution of a telescope is limited by its diffraction limit: the ratio of its observing wavelength to its diameter. Developments in quantum information theory over the past decade have uncovered quantum-optimal measurement methods that enable super-resolution imaging beyond the diffraction limit, and many laboratory-scale demonstrations of these methods have been performed over the past decade, culminating in the recent first on-sky demonstration of quantum-enhanced astronomical imaging. In this Review, we detail the current progress and achievements of these theoretical and experimental results, discuss the astronomical science cases motivating the development of higher resolution telescopes, summarise the technological challenges facing the practical application of quantum imaging technologies to astronomy, and present a vision for the realization of \emph{quantum telescopes} with imaging resolutions orders of magnitude better than current observatories.
Astrophotonics is a burgeoning field that lies at the interface of photonics and modern astronomical instrumentation. Here we provide a pedagogical review of basic photonic functions that enable modern instruments, and give an overview of recent and future applications. Traditionally, optical fibres have been used in innovative ways to vastly increase the multiplex advantage of an astronomical instrument, e.g. the ability to observe hundreds or thousands of stars simultaneously. But modern instruments are using many new photonic functions, some emerging from the telecom industry, and others specific to the demands of adaptive optics systems on modern telescopes. As telescopes continue to increase in size, we look to a future where instruments exploit the properties of individual photons. In particular, we envisage telescopes and interferometers that build on international developments in quantum networks, the so-called quantum internet. With the aid of entangled photons and quantum logic gates, the new infrastructures seek to preserve the photonic state and timing of individual photons over a coherent network.
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.
Quantum technologies may revolutionize optical interferometry through new means to distribute and preserve electric-field amplitude and phase correlations between widely separated telescopes. After reviewing existing techniques, I survey proposed quantum-sensing and quantum-networking applications and highlight recent laboratory demonstrations of key building blocks. By easing field-transport demands for baselines beyond $\sim$1 km, quantum-enhanced interferometry could enable sub-milliarcsecond imaging and microarcsecond-class differential astrometry.
That said, "going quantum" is not a magic shortcut to sensitivity because many of the most compelling science cases remain photon- and turbulence-limited. I therefore emphasize the practical constraints -- loss, bandwidth, coherence time, synchronization, and wavelength limits of quantum interfaces -- that must also be overcome to make these capabilities useful for astronomy, whether deployed on the ground or from space.