Simulating photonic devices with noisy optical elements

Quantum computers are inherently affected by noise. While in the long-term error correction codes will account for noise at the cost of increasing physical qubits, in the near-term the performance of any quantum algorithm should be tested and simulated in the presence of noise. As noise acts on the hardware, the classical simulation of a quantum algorithm should not be agnostic on the platform used for the computation. In this work, we apply the recently proposed noisy gates approach to efficiently simulate noisy optical circuits described in the dual rail framework. The evolution of the state vector is simulated directly, without requiring the mapping to the density matrix framework. Notably, we test the method on both the gate-based and measurement-based quantum computing models, showing that the approach is very versatile. We also evaluate the performance of a photonic variational quantum algorithm to solve the MAX-2-CUT problem. In particular we design and simulate an ansatz which is resilient to photon losses up to $p \sim 10^{-3}$ making it relevant for near term applications

Phase Noise in Real-World Twin-Field Quantum Key Distribution

We investigate the impact of noise sources in real-world implementations of Twin-Field Quantum Key Distribution (TF-QKD) protocols, focusing on phase noise from photon sources and connecting fibers. Our work emphasizes the role of laser quality, network topology, fiber length, arm balance, and detector performance in determining key rates. Remarkably, it reveals that the leading TF-QKD protocols are similarly affected by phase noise despite different mechanisms. Our study demonstrates duty cycle improvements of over 2x through narrow-linewidth lasers and phase-control techniques, highlighting the potential synergy with high-precision time/frequency distribution services. Ultrastable lasers, evolving toward integration and miniaturization, offer promise for agile TF-QKD implementations on existing networks. Properly addressing phase noise and practical constraints allows for consistent key rate predictions, protocol selection, and layout design, crucial for establishing secure long-haul links for the Quantum Communication Infrastructures under development in several countries.Comment: 18 pages, 8 figures, 2 table

Corrugated Waveguide Slow-Wave Structure for THz Travelling Wave Tube

THz applications require sources and amplifiers compact, lightweight and powerful. Vacuum electron devices are the candidate solution. Among others, the Corrugated Waveguide Slow-Wave Structure seems particularly suitable for Traveling Wave Tubes in the THz region. THz vacuum electron devices require high precision technological processes with high aspect ratio such as SU-8 process. However, fabrication tolerances could highly affect the overall performances. Therefore a statistical analysis is fundamental for a reliable design. In this summary it is proposed a method based on an analytical model of the corrugated waveguide together with the Pierce theory, to fastly compute the gain of corrugated waveguide vacuum traveling wave tubes. The method is validated by three-dimensional electromagnetic softwares, both for cold and hot parameters. The proved accuracy and fast computation time make the model suitable for performing the sensitivity analysis of the Corrugated waveguide Vacuum tube to be realized by SU-8 technology process

Packaged Single Pole Double Thru (SPDT) and True Time Delay Lines (TTDL) Based on RF MEMS Switches

Packaged MEMS devices for RF applications have been modelled, realized and tested. In particular, RF MEMS single ohmic series switches (SPST) have been obtained on silicon high resistivity substrates and they have been integrated in alumina packages to get single-pole-double-thru (SPDT) and true-time-delayline (TTDL) configurations. As a result, TTDLs for wide band operation, designed for the (6-18) GHz band, have been obtained, with predicted insertion losses less than 2 dB up to 14 GHz for the short path and 3 dB for the long path, and delay times in the order of 0.3-0.4 ns for the short path and 0.5-0.6 ns for the long path. The maximum differential delay time is in the order of 0.2 ns