Tests of the quantum superposition principle: current experiments on Earth, future experiments in Space

Pablo L. Saldanha, Nelson Yokomizo

We investigate surprising consequences of the hypothesis that gravity and proper time obey the quantum superposition principle. We show that, for a massive body prepared in a superposition of two positions and post-selected in a suitable final state, the elapsed proper time in another region of space can assume an anomalous effective value lying outside the range allowed by classical general relativity. Remarkably, the effective elapsed proper time can even become negative, corresponding to an effective evolution backward in time. We also propose an experiment to observe an anomalous effective proper time associated with the internal degrees of freedom of a quantum particle in an interferometer under Earth's gravitational field. The proposed experiment is, in principle, feasible with current technology, and its realization could provide the first experimental evidence of an interplay between quantum mechanics and general relativity beyond the effects of the Newtonian potential in flat spacetime.

Hendrik Ulbricht

Shih-Yuin Lin, B. L. Hu

Abstract Quantum information (QI) experiments applying quantum optics in outer space with a very long baseline may have advantages over the current Earth-bound experiments or the Earth-to-satellite experiments, because they can minimize the loss in light transmission and maximize the gain in time resolution. This future class of experiments, among them quantum teleportation and entanglement swapping, can shed light on many fundamental theoretical issues in gravitational quantum physics and relativistic QI. Regarding relativity theory, these experiments in an outer-space setting can involve observations at spacelike and timelike separations and explicate intriguing phenomena from different choices of time-slicing. Regarding QI, they may be able to ensure the causal independence of the expectation values in the Bell test. These issues are addressed in this paper with analysis and explanations.

G. C. Ghirardi

Mikhail Pavlov

Abstract As space missions—both manned and unmanned—expand beyond Earth’s orbit, the need for reliable and real-time communication between Earth and distant spacecraft becomes critical. Conventional radio-frequency communication is constrained by the speed of light, resulting in significant signal delays; for example, a message to Mars experiences a minimum one-way delay of approximately 8 minutes. Such delays hinder operational control and decision-making during critical maneuvers or emergencies. This paper explores quantum communication as a potential solution, leveraging quantum entanglement and superposition to establish instantaneous correlations between remote systems. By employing these quantum phenomena, it becomes theoretically possible to achieve real-time information exchange independent of conventional speed-of-light limitations. The study discusses foundational principles, potential implementation in space systems, and implications for future deep-space exploration.

Rainer Kaltenbaek