journal club on aspects of information, quantum theory, and gravity
This is the webpage for the InfoGraviton Journal Club. During the first quarter of 2025 (January–April) our meetings will (mostly) happen on Thursdays at 14:00 (America/Sao_Paulo). For questions, suggestions, and etc, contact Níck.
Thu, 09 Apr 2026, 14:00 (America/Sao_Paulo)
It was recently shown that black holes decohere any quantum superpositions in their vicinity. This decoherence is mediated by soft radiation through the horizon, and can be understood as the result of the fact that quantum states in the exterior source distinguishable states of long-range fields in the interior. To study this phenomenon and others, we extend Tomita-Takesaki theory to accommodate states of soft radiation such as arise in the electromagnetic and gravitational memory effects, and provide a general framework for computing the distinguishability of general coherent states. Applying these tools, we use the methods of unambiguous state discrimination and approximate quantum error correction to prove some new relations regarding the distinguishability of quantum states, and the quantum information content of soft radiation, and thereby show that a black hole (or any horizon) decoheres its environment as though its interior were full of optimal observers.
Thu, 23 Apr 2026, 14:00 (America/Sao_Paulo)
Caio César Rodrigues Evangelista
Void of any inherent structure in classical physics, the vacuum has revealed to be incredibly crowded with all sorts of processes in relativistic quantum physics. Yet, its direct effects are usually so subtle that its structure remains almost as evasive as in classical physics. Here, in contrast, we report on the discovery of a novel effect according to which the vacuum is compelled to play an unexpected central role in an astrophysical context. We show that the formation of relativistic stars may lead the vacuum energy density of a quantum field to an exponential growth. The vacuum-driven evolution which would then follow may lead to unexpected implications for astrophysics, while the observation of stable neutron-star configurations may teach us much on the field content of our Universe.
25 Mar 2026
Andrew J. Groszek and Charles W. Woffinden
What if every known communication channel were blocked: no radio, no light, no sound? Is physics out of options? In this talk, we’ll argue that it isn’t. We explore an unconventional idea: using gravity itself as a wireless communication channel. By simply moving a mass back and forth, a sender can modulate the local static gravitational field, which a distant receiver can detect using an off-the-shelf gravimeter. Unlike electromagnetic signals, gravity cannot be shielded, screened, or turned off—and that makes it a uniquely “unblockable” carrier of information.
We introduce the basic physics behind gravitational communication, show how it can be analysed as an antenna problem with well-defined data rates, directionality, and noise, and then present an experimental demonstration. Using nothing more exotic than an antiquated elevator and a 1980s gravimeter, we have successfully transmitted a 49-bit gravitational message through a brick wall. While this is not the future of high-bandwidth Wi-Fi, it opens up a surprisingly rich intersection of gravitation, information theory, and experimental ingenuity—and raises the delightful possibility that you really could communicate using gravity.
12 Mar 2026
Motivated by the increasing connections between information theory and high-energy physics, particularly in the context of the AdS/CFT correspondence, we explore the information geometry associated to a variety of simple systems. By studying their Fisher metrics, we derive some general lessons that may have important implications for the application of information geometry in holography. We begin by demonstrating that the symmetries of the physical theory under study play a strong role in the resulting geometry, and that the appearance of an AdS metric is a relatively general feature. We then investigate what information the Fisher metric retains about the physics of the underlying theory by studying the geometry for both the classical 2d Ising model and the corresponding 1d free fermion theory, and find that the curvature diverges precisely at the phase transition on both sides. We discuss the differences that result from placing a metric on the space of theories vs. states, using the example of coherent free fermion states. We compare the latter to the metric on the space of coherent free boson states and show that in both cases the metric is determined by the symmetries of the corresponding density matrix. We also clarify some misconceptions in the literature pertaining to different notions of flatness associated to metric and non-metric connections, with implications for how one interprets the curvature of the geometry. Our results indicate that in general, caution is needed when connecting the AdS geometry arising from certain models with the AdS/CFT correspondence, and seek to provide a useful collection of guidelines for future progress in this exciting area.