Projections as representations of phenomena

Nikolai Borisovich Melnikov, Boris Il'ich Reser

Niranjan Sridhar

My doctoral thesis details my research on two major projects. Both projects investigate the correspondence between the discrete (photon number) and the continuous (quadrature) representation of optical states. Understanding the relationships between the two representations is very important for the investigation of quantum physics phenomena. Moreover it has significant applications in quantum computing where it is found that discrete-variable bases are easier to error-correct but some continuous-variable architectures are more scalable. Research in the connection between the two representation might help develop new architectures for scalable fault-tolerant quantum computing.

Huang Pengjie

This work presents a conceptual and representational framework aimed at clarifying the structural relationships among established physical theories across relativistic, quantum, and cosmological regimes. Rather than proposing new dynamical laws, particles, or experimentally testable predictions, the manuscript focuses on how existing physical descriptions may be consistently interpreted within a unified representational structure. The proposed Dual-Spacetime Projection Framework distinguishes between an underlying descriptive domain and an observed effective spacetime, connected through a scale-dependent projection. This distinction is intended as a formal and interpretative tool, not as an ontological claim about the existence of multiple physical spacetimes. Within this perspective, several foundational features of modern physics—such as Lorentz invariance, finite signal propagation, quantum uncertainty, and large-scale cosmological behavior—are discussed as consequences of representational structure rather than as independent postulates. The manuscript is positioned as a contribution to the foundations of theoretical physics, offering a coherent conceptual lens for organizing and interpreting existing theories. It is intended for readers interested in foundational questions, conceptual unification, and the representational aspects of physical law, and does not rely on experimental data or numerical simulation.

Louis Fein

Kalervo V. Laurikainen

Philipp Schleich, Tyler Kharazi, Xiangyu Li +3 more

Complicated boundary conditions are essential to accurately describe phenomena arising in nature and engineering. Recently, the investigation of a potential speedup through quantum algorithms in simulating the governing ordinary and partial differential equations of such phenomena has gained increasing attention. We design an efficient quantum algorithms for solving differential equations with arbitrary boundary conditions. Specifically, we propose an approach to enforce arbitrary boundary conditions and constraints through adding a penalty projection to the governing equations. Assuming a fast-forwardable representation of the projection to ensure an efficient interaction picture imulation, the cost of to enforce the constraints is at most $O(\logλ)$ in the strength of the penalty $λ$ in the gate complexity; in the worst case, this goes as $O([\|v(0)\|^2\|A_0\| + \|b\|_{L^1[0;t]}^2)]t^2/\varepsilon)$, for precision $\varepsilon$ and a dynamical system $\frac{\rm d}{{\rm d}t} v(t) = A_0(t) v(t) + b(t)$ with negative semidefinite $A_0(t)$ of size $n^d\times n^d$. E.g., for the heat equation, this leads to a gate complexity overhead of $\widetilde O(d\log n + \log t)$. We show constraint error bounds for the penalty approach and provide validating numerical experiments, and estimate the circuit complexity using the Linear Combination of Hamiltonian Simulation.