Towards satellite tests combining general relativity and quantum mechanics through quantum optical interferometry: progress on the deep space quantum link
Makan Mohageg,
Charis Anastopoulos,
Olivia Brasher,
Jason Gallicchio,
Bei Lok Hu,
Thomas Jennewein,
Spencer Johnson,
Shih-Yuin Lin,
Alexander Ling, et al.
EPJ Quantum Technology
12
78
(2025)
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The Deep Space Quantum Link (DSQL) is a space-mission concept that aims to explore the interplay between general relativity and quantum mechanics using quantum optical interferometry. This mission concept was formally presented to the United States National Academy of Science Decadal Survey as a research campaign for Fundamental Physics in 2022. Since then, advances have been made in the space-based quantum optical technologies required to conduct a DSQL-type mission. In addition, other research efforts have defined alternative measurement concepts to explore the same scientific questions motivating the DSQL mission. This paper serves as an update to the community on the status of the DSQL mission concept and related research and technology development efforts.
Indistinguishable MHz-narrow heralded photon pairs from a whispering gallery resonator
Sheng-Hsuan Huang,
Thomas Dirmeier,
Golnoush Shafiee,
Kaisa Laiho,
Dmitry Strekalov,
Andrea Aiello,
Gerd Leuchs,
Christoph Marquardt
The Hong–Ou–Mandel interference plays a vital role in many quantum optical applications where indistinguishability of two photons is important. Such photon pairs are commonly generated as the signal and idler in the polarization-degenerate spontaneous parametric downconversion (SPDC). To scale this approach to a larger number of photons, we demonstrate how two independent signal photons radiated into different spatial modes can be rendered conditionally indistinguishable by a heralding measurement performed on their respective idlers. We use the SPDC in a whispering gallery resonator, which is already proven to be versatile sources of quantum states. Its extreme conversion efficiency allowed us to perform our measurements with only 50 nW of in-coupled pump power in each propagation direction. The Hong–Ou–Mandel interference of two counterpropagating signal photons manifested itself in the fourfold coincidence rate, where the detection of two idler photons heralds a pair of signal photons with a desired temporal overlap. We achieved the Hong–Ou–Mandel dip contrast of 74% ± 5%. Importantly, the optical bandwidth of all involved photons is of the order of a MHz and is continuously tunable. This, on the one hand, makes it possible to achieve the necessary temporal measurement resolution with standard electronics and, on the other hand, creates a quantum state source compatible with other candidates for qubit implementation, such as optical transitions in solid-state or vaporous systems. We also discuss the possibility of generating photon pairs with similar temporal modes from two different whispering gallery resonators.
Inequality-free proof of Bell's theorem
Andrea Aiello
Physical Review A
111
032204
(2025)
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Many of the tests of local realistic hidden-variable theories against quantum mechanics are based on inequalities such as Bell's inequality and Clauser Horne, Shimony, and Holt's inequality. In this work we present a simple alternative test which does not involve inequalities, but direct comparison between correlation functions. The main advantage of this test is that it does not require measuring incompatible observables separately and simultaneously. This implies that our result, differently from traditional inequalities, does not involve counterfactual reasoning.
Contact
Research Group Christoph Marquardt
Max Planck Institute for the Science of Light Staudtstr. 2 91058 Erlangen, Germany
