Scientific Series

High-rate quantum low-density parity-check (qLDPC) codes offer significantly lower encoding overhead compared to their topological counterparts by relaxing locality constraints. However, achieving full-fledged logical computation with these codes in physical systems with low space-time costs remains a formidable challenge. In the first part of this talk, I will provide an overview of recent advancements in implementing qLDPC codes as quantum memories on realistic platforms, such as reconfigurable atom arrays. Next, I will present a new scheme for performing parallelizable and locally addressable logical operations on homological product codes. This scheme extends the transversal CNOT gate from two identical CSS codes to two distinct, yet structurally similar, qLDPC codes, enabling efficient local addressing of collectively encoded information. We demonstrate that this approach achieves lower overhead in not only the space- but also the overall space-time overhead compared to surface-code-based computations. Finally, I will discuss new strategies for achieving highly space-time-efficient computations with qLDPC codes by leveraging algorithm-specific fault tolerance, designing tailored protocols for structured quantum algorithms.

Recent efforts to formulate a unified, causally neutral approach to quantum theory have highlighted the need for a framework treating spatial and temporal correlations on an equal footing. Building on this motivation, we propose operationally inspired axioms for quantum states over time, demonstrating that, unlike earlier approaches, these axioms yield a unique quantum state over time that is valid across both bipartite and multipartite spacetime scenarios. In particular, we show that the Fullwood-Parzygnat state over time uniquely satisfies these axioms, thus unifying bipartite temporal correlations and extending seamlessly to any number of temporal points. In particular, we identify two simple assumptions—linearity in the initial state and a quantum analog of conditionability—that single out a multipartite extension of bipartite quantum states over time, giving rise to a canonical generalization of Kirkwood-Dirac type quasi-probability distributions. This result provides a new characterization of quantum Markovianity, advancing our understanding of quantum correlations across both space and time.

In this talk, I will explain the concept of fault tolerance, which ensures reliable quantum computation. Building on recent advancements in mixed-state phases of matter, I introduce a new diagnostic called the spacetime Markov length. The divergence of this length scale signals the intrinsic breakdown of fault tolerance.

In January 2024, the Laser Interferometer Space Antenna (LISA) mission was officially adopted by the European Space Agency, marking a new era in gravitational wave astronomy. LISA will be the first space-based gravitational wave detector, designed to explore the cosmos in the millihertz frequency range. This talk will present the mission's key scientific objectives and how the scientific community is preparing for the exploitation of LISA data. I will discuss the anticipated source types and the fundamental questions they could help answer. Then, we will focus on Extreme Mass Ratio Inspirals (EMRIs), a class of sources where small compact objects orbit the massive black holes at the centers of galaxies. These systems hold immense scientific potential for the LISA mission, as they encode a detailed map of the spacetime around the massive black hole. I will discuss how future detections of EMRIs can be used to constrain parameters related to accretion disks and modifications of General Relativity. Finally, I will highlight the path forward in preparing for LISA's launch and how to get involved in contributing to the mission scientific success. 

In this talk, I will discuss how one can use the gravitational path integral to compute the supersymmetric index of black holes as well as other black objects in string theory. The saddles that I shall describe admit a non-zero temperature, consequently lacking an infinitely long AdS throat that separates the horizon from the asymptotic region, and also admit periodic boundary conditions for fermionic fields around the thermal circle, consequently counting bosonic and fermionic states with an opposite sign. Since the microscopic calculation of these indices is oftentimes well understood yet the saddles that I shall describe now lack the conventional decoupling limit taken in AdS/CFT, our analysis represents a first step towards understanding holography for supersymmetric observables in flat space.

In the panel discussion, each panelist will showcase examples of well-written papers and share one essential "do" and one important "don't" for crafting effective scientific papers. The session will include an open Q&A segment to encourage audience engagement.

the no-cloning theorem is an essential result in quantum information on top of which many quantum cryptography protocols are built. In this talk we examine the cloning question in the context of classical mechanics/Hamiltonian mechanics. We find the answer is quite subtle: whether a mechanical system can be cloned depends on the topological structure of its phase space. In particular, for a system to be clonable, its phase space must be contractible. This means certain systems (e.g. particle moving on a line) is clonable, while others (e.g. the simple pendulum) cannot be cloned. We explain the idea of the proof, which uses tools from algebraic topology (homotopy groups and Whitehead’s theorem). Finally we discuss the physical interpretations of this result: how do we reconcile this theorem with the experience that generally speaking, classical information is clonable? Can we use this no-cloning theorem to build secure communication protocols in classical systems instead of quantum ones?

The Celestial Holography conjecture posits the existence of a codimension two theory whose correlators compute the S-matrix in a conformal primary basis. Although resembling a CFT in several respects, the intrinsic definition of this proposed dual theory remains elusive. In this talk, I will discuss a conjecture suggesting that Celestial CFT (CCFT) is related to a dimensionally reduced CFT on the Lorentzian cylinder and present some concrete examples of celestial amplitudes constructed in this way.