Fundamental Limits of Thermal-noise Lossy Bosonic Multiple Access Channel

Bosonic channels describe quantum-mechanically many practical communication links such as optical, microwave, and radiofrequency. We investigate the maximum rates for the bosonic multiple access channel (MAC) in the presence of thermal noise added by the environment and when the transmitters utilize Gaussian state inputs. We develop an outer bound for the capacity region for the thermal-noise lossy bosonic MAC. We additionally find that the use of coherent states at the transmitters is capacity-achieving in the limits of high and low mean input photon numbers. Furthermore, we verify that coherent states are capacity-achieving for the sum rate of the channel. In the non-asymptotic regime, when a global mean photon-number constraint is imposed on the transmitters, coherent states are the optimal Gaussian state. Surprisingly however, the use of single-mode squeezed states can increase the capacity over that afforded by coherent state encoding when each transmitter is photon number constrained individually.Comment: 8 pages, 3 figure

VLA Limits for Intermediate Mass Black Holes in Three Globular Clusters

The observational evidence for central black holes in globular clusters has been argued extensively, and their existence has important consequences for both the formation and evolution of the cluster. Most of the evidence comes from dynamical arguments, but the interpretation is difficult, given the short relaxation times and old ages of the clusters. One of the most robust signatures for the existence of a black hole is radio and/or X-ray emission. We observed three globular clusters, NGC6093 (M80), NGC6266 (M62), and NGC7078 (M15), with the VLA in the A and C configuration with a 3-sigma noise of 36, 36 and 25 microJy, respectively. We find no statistically-significant evidence for radio emission from the central region for any of the three clusters. NGC6266 shows a 2-sigma detection. It is difficult to infer a mass from these upper limits due to uncertainty about the central gas density, accretion rate, and accretion model.Comment: 5 pages, accepted for publication in the Astronomical Journa

Covert Quantum Communication Over Optical Channels

We explore the problem of covertly communicating qubits over the lossy thermal-noise bosonic channel, which is a quantum-mechanical model of many practical channels, including optical. Covert communication ensures that an adversary is unable to detect the presence of transmissions, which are concealed in channel noise. We investigate an achievable lower bound on quantum covert communication using photonic dual-rail qubits. This encoding has practical significance, as it has been proposed for long-range repeater-based quantum communication over optical channels

Good for the planet and good for our health: the evidence for whole-food plant-based diets

There is growing interest in the health and environmental benefits of whole-food plant-based (WFPB) diets. The current global food system is harmful to our planet and is a key driver of climate change, pollution and biodiversity loss. A transition to WFPB diets will mitigate against these impacts and potentially reduce greenhouse gas emissions by up to 80%. Emerging evidence suggests that such diets also have significant physical and mental health benefits and can be useful in preventing and treating a range of conditions. Psychiatrists therefore have an important role to play in promoting WFPB diets among patients

Statistical-mechanical lattice models for protein-DNA binding in chromatin

Statistical-mechanical lattice models for protein-DNA binding are well established as a method to describe complex ligand binding equilibriums measured in vitro with purified DNA and protein components. Recently, a new field of applications has opened up for this approach since it has become possible to experimentally quantify genome-wide protein occupancies in relation to the DNA sequence. In particular, the organization of the eukaryotic genome by histone proteins into a nucleoprotein complex termed chromatin has been recognized as a key parameter that controls the access of transcription factors to the DNA sequence. New approaches have to be developed to derive statistical mechanical lattice descriptions of chromatin-associated protein-DNA interactions. Here, we present the theoretical framework for lattice models of histone-DNA interactions in chromatin and investigate the (competitive) DNA binding of other chromosomal proteins and transcription factors. The results have a number of applications for quantitative models for the regulation of gene expression.Comment: 19 pages, 7 figures, accepted author manuscript, to appear in J. Phys.: Cond. Mat