The European Research Council has awarded almost 9 million euros to MIT’s Nergis Mavalvala, the University of Vienna’s Philip Walther and Piotr Chruściel, and the University of Munich LMU’s Georgi Dvali to investigate the influence of gravity on light quanta. The ERC Synergy Grant “GRAVITES” will perform experiments at the interface of quantum physics and general relativity. GRAVITES aims to combine four complementary disciplines: quantum photonics and precision interferometry guided by expertise in general relativity and quantum field theory. The synergy among the research groups will realize a large-scale fiber interferometer with an unprecedented level of precision. These experiments will probe the effect of Einstein’s gravity on relativistic quantum systems by measuring the influence of the Earth’s gravitational field on entangled states of light.

Led by Walther, the grant brings together two experimental and two theoretical groups. The experiment is being carried out by Nergis Mavalvala, an expert in precision interferometry, and her research group at MIT’s Laser Interferometer Gravitational-Wave Observatory (LIGO), and Philip Walther, whose expertise lies in quantum control of entangled photons. Piotr Chruściel and Georgi Dvali, renowned researchers in the field of general relativity and quantum field theory, respectively, are members of the GRAVITES theoretical team.

The GRAVITES experiment will probe the effect of Einstein’s gravity on relativistic quantum systems by measuring the influence of the Earth’s gravitational field on entangled states of light. To do so, the sensitivity required of GRAVITES’s apparatus will have to exceed all present large-scale fiber-based interferometers by several orders of magnitude. The two experimental teams must combine cutting-edge technologies in precision interferometry (Mavalvala) and entangled photons (Walther) to achieve the required sensitivity. In parallel, the theory team will investigate the combined effects of gravitation (Cruzciel) and field quantization (Dvali) in dielectric waveguides. “This is precisely the team you need to bring together to address deep – and largely unanswered –  questions about how gravity interacts with the quantum world,” Mavalvala says excitedly.

Within the next six years, the ERC team aims to answer a key question in science, whether entangled quantum states satisfy the predictions of relativistic quantum field theory in a curved spacetime. “This ERC Synergy Grant will enable us to observe for the first time how entangled states gravitate”, says Philip Walther. “This has wide range of important implications for fundamental physics and for its observational manifestations, which spans from understanding the classical gravitational influence on entangled particles that likely store quantum information in black holes, all the way, to probing new physics that influences quantum properties of entangled photons”, says Dvali.

Besides the fundamental impact, the technology developed for this project will be beneficial for research fields such as quantum cryptography and quantum metrology, relativistic geodesy, and frequency dissemination.

Mavalvala, the Curtis and Kathleen Marble Professor of Astrophysics and dean of MIT’s School of Science, works in the field of experimental gravitational-wave (GW) detection and quantum measurement, and has spent her career developing precision optical technologies for LIGO. Mavalvala’s group, which is part of the MIT Kavli Institute for Astrophysics and Space Research (MKI) LIGO Laboratory, focuses on developing techniques to measure and circumvent quantum noise limits, and to manipulate quantum states to improve the performance of GW detectors. Her group has also done pioneering experiments using light forces to optically cool and trap macroscopic objects with the goal of observing quantum behavior in human-scale objects. GRAVITES marks an exciting new direction for her group, working for the first time with single photons and precision optical fiber interferometers.

The European Research Council announcement stated that almost 360 proposals were submitted in this first ERC Synergy Grant call under the EU’s Horizon Europe program. The 29 winning projects, including GRAVITES, involve 105 principal investigators who will carry out their research at universities and research centers in 19 countries.