arXiv subjects

Joseph Chapman

Publications and source records attributed to Joseph Chapman.

4 recordsLinked to original sources

arXiv2026

The Widom line in the Ising model on a decorated bilayer lattice

There has been much recent interest devoted to a class of frustrated one-dimensional statistical mechanics lattice models which exhibit sharp thermodynamics. In this work, we study an extension of one of these models to two dimensions; the Ising model on a decorated bilayer lattice. We show that the pseudo-transitions of the one-dimensional models become a real first order phase transition in this two-dimensional analogue. Moreover, the pseudo-transition is found to still exist above a bi-critical point. This can be characterised as a Widom line, which allows a re-interpretation of the physics in the previously studied one-dimensional models.

cond-mat.stat-mech↗

arXiv2025

Drone- and Vehicle-Based Quantum Key Distribution

Quantum key distribution is a point-to-point communication protocol that leverages quantum mechanics to enable secure information exchange. Commonly, the transmitter and receiver stations are at fixed locations, and the single-photon quantum states are transmitted over fiber or free space. Here, we describe a modular, platform-agnostic, quantum key distribution transmitter and receiver with reduced size, weight, and power consumption to realize a mobile quantum communication system. We deploy the system on different moving platforms, demonstrating drone-to-drone, drone-to-vehicle, and vehicle-to-vehicle quantum communication, achieving secure key rates in the finite-key regime in the range of 1.6 - 20 kbps. To prove the security of the system, we develop advanced physics models of the devices that account for non-ideal behaviors that are of greater importance in mobile platforms. The modular system can be easily upgraded to include sources of entangled photonic quantum states, which will find application in future quantum networks.

quant-ph↗

arXiv2024

Bifurcation in correlation length of the Ising model on a "Toblerone" lattice

The classical Ising chain is the paradigm for the non-existence of phase transitions in 1D systems and was solved by Ernst Ising one hundred years ago. More recently, a decorated two leg Ising ladder has received interest for the curious thermodynamics that resemble a phase transition; a sharp peak in the specific heat at low, but finite temperature. We use this model to reveal a bifurcation in the correlation lengths due to a crossing of the sub-leading eigenvalues of the transfer matrix, which results in two distinct length scales necessary to describe to the decay of correlations. We discuss this phenomenon in the context of the geometric frustration in the model. We also provide additional results to aid in the understanding of the curious thermodynamics of the model through a study of the magnetic susceptibilities.

cond-mat.stat-mech↗

arXiv2017

Quantum-memory-assisted multi-photon generation for efficient quantum information processing

In the last two decades, many quantum optics experiments have demonstrated small-scale quantum information processing applications with several photons. Beyond such proof-of-principle demonstrations, efficient preparation of large, but definite, numbers of photons is of great importance for further scaling up and speeding up photonic quantum information processing. Typical single-photon generation techniques based on nonlinear parametric processes face challenges of probabilistic generation. Here we demonstrate efficient synchronization of photons from multiple nonlinear parametric heralded single-photon sources (HSPSs), using quantum memories (QMs). Our low-loss optical memories greatly enhance (~30x) the generation rate of coincidence photons from two independent HSPSs, while maintaining high indistinguishability (95.7%) of the synchronized photons. As an application, we perform the first demonstration of HSPS-based measurement-device-independent quantum key distribution (MDI-QKD). The synchronized HSPSs demonstrated here will pave the way toward efficient quantum communication and larger scale optical quantum computing.

quant-ph↗