Quantum physics experiments in space using entangled photons and satellites are within reach of current technology. We propose a series of fundamental quantum physics experiments that make advantageous use of the space infrastructure with specific emphasis on the satellite-based distribution of entangled photon pairs. The experiments are feasible already today and will eventually lead to a Bell-experiment over thousands of kilometers, thus demonstrating quantum correlations over distances which cannot be achieved by purely earth-bound experiments.
Quantum physics experiments in space using entangled photons and satellites are within reach of current technology. We propose a series of fundamental quantum physics experiments that make advantageous use of the space infrastructure with specific emphasis on the satellite-based distribution of entangled photon pairs. The experiments are feasible already today and will eventually lead to a Bell-experiment over thousands of kilometers, thus demonstrating quantum correlations over distances which cannot be achieved by purely earth-bound experiments.
Space has always been a primary source of inspiration for the development of the scientific, technological, artistic, philosophical and religious thinking of the whole humankind. Space explorations marked the history of the XX century, bringing an incredible technological advancement and allowing to investigate the natural phenomena over scales and into details which are simply not available on Earth. Nowadays, the Space is the benchmark of the new quantum revolution, which promises to change the way we communicate, measure and calculate, thank to the exploitation and the control of what happens at the microscopic scale. Indeed, the quantum theory, born at the beginning of the XX century to describe the behavior of the elementary particles of Nature, has reached today an incredible reliability. As any scientific theory, Quantum Mechanics is valid within the limits in which it has been experimentally verified, and the Space is the main stage where to validate quantum predictions at large scales, in a domain that is completely different with respect to the microscopic one from which it moved. The technological advances in photonics, which allows the manipulation and the control of the single quanta of light, the photons, make today feasible fundamental tests of Quantum Mechanics in Space, experiments to investigate, for example, if entanglement is preserved along thousands of kilometers or if the wave-particle duality survives even after a Space trip. Furthermore, Space makes available relativistic regimes, in which the velocities and the distances could allow to experimentally investigate the unresolved puzzle of modern physics, that is, the interplay between Quantum Mechanics and gravitation. For these reasons, this thesis is dedicated to the Quantum Optics experiment in Space I have been involved during my PhD.
Space offers a very unique environment for quantum physics experiments at regimes of distance and velocity not possible on ground. In the recent years there have been a range of theoretical and experimental studies towards the feasibility of performing quantum physics and quantum information science experiments in space. Such a system is possible with today's technologies and would allow to demonstrate the application of quantum secured transmission, and perform quantum optics science tests. In the near term the most promising approach is using a low-earth-orbiting (LEO) satellite either as an independent nano-sat, a piggyback payload on a larger mission, or even on the International Space Station (ISS). I will outline the envisioned quantum experiments and the requirements for the technology.
Long-distance, entanglement distribution over thousands of kilometers is necessary to build a global-scale quantum network. Directly transferring entangled, telecom photons through fiber is relatively straight forward in local networks where the separation between nodes is below 100 km, corresponding to a 1% transmission. However, the exponentially greater loss at larger distances (e.g. only 10−6 transmission at 300 km) leads to unacceptably low transmission rates, which drop below the noise rates of typical photon detectors. Alternatively, the Earth’s rarefied atmosphere at high altitudes reduces the absorption and scattering of infrared photons. Therefore, free-space links between satellite and ground stations have been shown to enable entangled photon transmission over 2000 km. While this demonstration showed the viability of satellite-enhanced entanglement distribution, the source used in this demonstration produced distinguishable photons, which cannot be used for many fundamental protocols like teleportation. We are building a testbed to demonstrate the feasibility of distributing entangled, indistinguishable photons over a space-to-ground link using entanglement swapping.
Physical theories are developed to describe phenomena in particular regimes, and generally are valid only within a limited range of scales. For example, general relativity provides an effective description of the Universe at large length scales, and has been tested from the cosmic scale down to distances as small as 10 meters. In contrast, quantum theory provides an effective description of physics at small length scales. Direct tests of quantum theory have been performed at the smallest probeable scales at the Large Hadron Collider, ∼10−20 meters, up to that of hundreds of kilometers. Yet, such tests fall short of the scales required to investigate potentially significant physics that arises at the intersection of quantum and relativistic regimes. We propose to push direct tests of quantum theory to larger and larger length scales, approaching that of the radius of curvature of spacetime, where we begin to probe the interaction between gravity and quantum phenomena. In particular, we review a wide variety of potential tests of fundamental physics that are conceivable with artificial satellites in Earth orbit and elsewhere in the solar system, and attempt to sketch the magnitudes of potentially observable effects. The tests have the potential to determine the applicability of quantum theory at larger length scales, eliminate various alternative physical theories, and place bounds on phenomenological models motivated by ideas about spacetime microstructure from quantum gravity. From a more pragmatic perspective, as quantum communication technologies such as quantum key distribution advance into Space towards large distances, some of the fundamental physical effects discussed here may need to be taken into account to make such schemes viable.
Significant work has been done to develop quantum satellites, which generate entangled pairs in space and distribute them to ground stations separated some distance away. The reverse “uplink” case, where pairs are generated on the ground and swapped on the satellite using an optical Bell measurement, has not been seriously considered due to a prevailing assumption that it is practically infeasible. In this paper, we illustrate the feasibility of performing Discrete Variable photonic Bell measurements in space by conducting a detailed numerical analysis to estimate the channel efficiency and attainable pair fidelity for various satellite-station configurations. Our model accounts for a wide range of physical effects such as atmospheric effects, stray photons, and mode mismatch. Our findings show promise toward the feasibility of photonic Bell measurements in space, which motivates future research toward large-scale satellite-based uplink entanglement distribution.