Optimal quantum communication networks: capacitance versus security

https://arxiv.org/abs/2312.04221

The rate and security of quantum communications between users placed at arbitrary points of a quantum communication network depend on the structure of the network, on its extension and on the nature of the communication channels. In this work we propose a strategy of network optimization that intertwines classical network approaches and quantum information theory. Specifically, by suitably defining a quantum efficiency functional, we identify the optimal quantum communication connections through the network by balancing security and the quantum communication rate. The optimized network is then constructed as the network of the maximal quantum efficiency connections and its performance is evaluated by studying the scaling of average properties as functions of the number of nodes and of the network spatial extension.

Nature Photonics on the Plenary at CLEO/EUROPE-EQEC 2023

Rachel Won in The power of light-driven computing highlights the plenary talk in CLEO/EUROPE-EQEC 2023 about photonic computing machines in Nature Photonics.

CLEO Europe 2023
Cleo Europe 2023

See https://www.cleoeurope.org/photos/

QFT in curved spacetime permits quantitative predictions for the Unruh effect with hydrogenlike atoms

https://link.aps.org/doi/10.1103/PhysRevA.108.022807

We consider ionized hydrogenlike atoms accelerated by an external electric field to detect Unruh radiation. By applying quantum field theory in the Rindler space-time, we show that the first-quantized description for hydrogenlike atoms cannot always be adopted. This is due to the frame-dependent definition of particles as positive and negative frequency field modes. We show how to suppress such a frame-dependent effect by constraining the atomic ionization and the electric field. We identify the physical regimes with nonvanishing atomic excitation probability due to the Unruh electromagnetic background. We recognize the observational limits for the Unruh effect via first-quantized atomic detectors, which appear to be compatible with current technology. Notably, the nonrelativistic energy spectrum of the atom cannot induce coupling with the thermal radiation, even when special relativistic and general relativistic corrections are considered. On the contrary, the coupling with the Unruh radiation arises because of relativistic hyperfine splitting and the Zeeman effect.

Exponential improvement in combinatorial optimization by hyperspins

Classical or quantum physical systems can simulate the Ising Hamiltonian for large-scale optimization and machine learning. However, devices such as quantum annealers and coherent Ising machines suffer an exponential drop in the probability of success in finite-size scaling. We show that by exploiting high dimensional embedding of the Ising Hamiltonian and subsequent dimensional annealing, the drop is counteracted by an exponential improvement in the performance. Our analysis relies on extensive statistics of the convergence dynamics by high-performance computing. We propose a realistic experimental implementation of the new annealing device by off-the-shelf coherent Ising machine technology. The hyperscaling heuristics can also be applied to other quantum or classical Ising machines by engineering nonlinear gain, loss, and non-local couplings.

Hyperscaling in the coherent hyperspin machine

https://arxiv.org/abs/2308.02329