Quantum simulation of spin ordering with nuclear spins in a solid state lattice

An experiment demonstrating the quantum simulation of a spin-lattice Hamiltonian is proposed. Dipolar interactions between nuclear spins in a solid state lattice can be modulated by rapid radio-frequency pulses. In this way, the effective Hamiltonian of the system can be brought to the form of an antiferromagnetic Heisenberg model with long range interactions. Using a semiconducting material with strong optical properties such as InP, cooling of nuclear spins could be achieved by means of optical pumping. An additional cooling stage is provided by adiabatic demagnetization in the rotating frame (ADRF) down to a nuclear spin temperature at which we expect a phase transition from a paramagnetic to antiferromagnetic phase. This phase transition could be observed by probing the magnetic susceptibility of the spin-lattice. Our calculations suggest that employing current optical pumping technology, observation of this phase transition is within experimental reach.Comment: 11 pages, 3 figues; Published versio

Single vortex-antivortex pair in an exciton polariton condensate

In a homogeneous two-dimensional system at non-zero temperature, although there can be no ordering of infinite range, a superfluid phase is predicted for a Bose liquid. The stabilization of phase in this superfluid regime is achieved by the formation of bound vortex-antivortex pairs. It is believed that several different systems share this common behaviour, when the parameter describing their ordered state has two degrees of freedom, and the theory has been tested for some of them. However, there has been no direct experimental observation of the phase stabilization mechanism by a bound pair. Here we present an experimental technique that can identify a single vortex-antivortex pair in a two-dimensional exciton polariton condensate. The pair is generated by the inhomogeneous pumping spot profile, and is revealed in the time-integrated phase maps acquired using Michelson interferometry, which show that the condensate phase is only locally disturbed. Numerical modelling based on open dissipative Gross-Pitaevskii equation suggests that the pair evolution is quite different in this non-equilibrium system compared to atomic condensates. Our results demonstrate that the exciton polariton condensate is a unique system for studying two-dimensional superfluidity in a previously inaccessible regime

Geotechnical Characterization of Fine-Grained Spoil Material from Surface Coal Mines

Coal mines produce large amounts of excavated waste soils, known as spoils. These materials can cover vast areas, are typically dumped in heaps without any treatment and are difficult to exploit for engineering purposes because of their significant variability. Efficient exploitation of spoil heaps poses engineering challenges, related mainly to the involved degree of uncertainty. A small number of studies have attempted to characterize the geotechnical properties of spoil material; however, there remains a considerable gap in understanding how to deal with spoil materials in the context of sustainable development and civil infrastructure design. In this work, a systematic effort is made to quantify the uncertainty of the geotechnical properties of a particular spoil heap. Laboratory test results based on an extended investigation of a spoil material originating from lignite coal mines are gathered in one database and thoroughly analyzed. The results reveal and quantify the significant spoil material variability, which is contrasted against data for common soils, while a systematic approach is proposed for spoil material characterization

Temperature and wavelength drift tolerant WDM transmission and routing in on-chip silicon photonic interconnects

We demonstrate a temperature and wavelength shift resilient silicon transmission and routing interconnect system suitable for multi-socket interconnects, utilizing a dual-strategy CLIPP feedback circuitry that safeguards the operating point of the constituent photonic building blocks along the entire on-chip transmission-multiplexing-routing chain. The control circuit leverages a novel control power-independent and calibration-free locking strategy that exploits the 2nd derivative of ring resonator modulators (RMs) transfer function to lock them close to the point of minimum transmission penalty. The system performance was evaluated on an integrated Silicon Photonics 2-socket demonstrator, enforcing control over a chain of RM-MUX-AWGR resonant structures and stressed against thermal and wavelength shift perturbations. The thermal and wavelength stress tests ranged from 27 degrees C to 36 degrees C and 1309.90 nm to 1310.85 nm and revealed average eye diagrams Q-factor values of 5.8 and 5.9 respectively, validating the system robustness to unstable environments and fabrication variations. (C) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreemen

Vortices in polariton OPO superfluids

This chapter reviews the occurrence of quantised vortices in polariton fluids, primarily when polaritons are driven in the optical parametric oscillator (OPO) regime. We first review the OPO physics, together with both its analytical and numerical modelling, the latter being necessary for the description of finite size systems. Pattern formation is typical in systems driven away from equilibrium. Similarly, we find that uniform OPO solutions can be unstable to the spontaneous formation of quantised vortices. However, metastable vortices can only be injected externally into an otherwise stable symmetric state, and their persistence is due to the OPO superfluid properties. We discuss how the currents charactering an OPO play a crucial role in the occurrence and dynamics of both metastable and spontaneous vortices.Comment: 40 pages, 16 figure

Topological order and thermal equilibrium in polariton condensates

We report the observation of the Berezinskii-Kosterlitz-Thouless transition for a 2D gas of exciton-polaritons, and through the joint measurement of the first-order coherence both in space and time we bring compelling evidence of a thermodynamic equilibrium phase transition in an otherwise open driven/dissipative system. This is made possible thanks to long polariton lifetimes in high-quality samples with small disorder and in a reservoir-free region far away from the excitation spot, that allow topological ordering to prevail. The observed quasi-ordered phase, characteristic for an equilibrium 2D bosonic gas, with a decay of coherence in both spatial and temporal domains with the same algebraic exponent, is reproduced with numerical solutions of stochastic dynamics, proving that the mechanism of pairing of the topological defects (vortices) is responsible for the transition to the algebraic order. Finally, measurements in the weak-coupling regime confirm that polariton condensates are fundamentally different from photon lasers and constitute genuine quantum degenerate macroscopic states

3D Numerical Analysis for the Valorization Potential of Spoil Heaps by Shallow Foundations

Coal has been an energy source exploited for several decades, with its extraction being linked to creating wastes. Surface mines’ overburden and interburden materials are typically dumped in spoil heaps, many times without considering their future use. Nowadays, sustainability and circular economy principles demand the efficient valorization of these areas. In that vein, this work investigates alternatives from a geotechnical perspective with shallow foundations for the reclamation of a massive spoil heap. Initially, the installation with a raft foundation of a wind turbine was investigated through a serviceability limit envelope employing 3D finite element analysis. However, the spoil material is too soft to withstand such a massive superstructure, and more advanced foundation techniques are needed. Moreover, the installation of supportive constructions was examined, i.e., buildings with shallow isolated footings using a similar approach and 3D finite element analysis. The soil-footing response is much dependent on the constitutive model, and the potential of small buildings requires further attention. Overall, for the appropriate valorization of the spoil heap, it appears that ground improvement or deep foundations are necessary. This conclusion stands for many similar spoil heaps globally due to the material’s nature

Geotechnical Characterization of Fine-Grained Spoil Material from Surface Coal Mines

Coal mines produce large amounts of excavated waste soils, known as spoils. These materials can cover vast areas, are typically dumped in heaps without any treatment, and are difficult to exploit for engineering purposes because of their significant variability. Efficient exploitation of spoil heaps poses engineering challenges, related mainly to the involved degree of uncertainty. A small number of studies have attempted to characterize the geotechnical properties of spoil material; however, there remains a considerable gap in understanding how to deal with spoil materials in the context of sustainable development and civil infrastructure design. In this work, a systematic effort is made to quantify the uncertainty of the geotechnical properties of a particular spoil heap. Laboratory test results based on an extended investigation of a spoil material originating from lignite coal mines are gathered in one database and thoroughly analyzed. The results reveal and quantify the significant spoil material variability, which is contrasted against data for common soils, while a systematic approach is proposed for spoil material characterization.This material may be downloaded for personal use only. Any other use requires prior permission of the American Society of Civil Engineers. This material may be found at https://ascelibrary.org/doi/10.1061/%28ASCE%29GT.1943-5606.0002550

8×40 Gbps WDM amplification in a monolithically integrated Al2O3:Er3+-Si3N4waveguide amplifier

On chip waveguide optical amplifiers have been extensively studied over the last years, with a wide variety of materials tested and proposed for different applications. Among the most prominent solutions for on-chip amplification, erbium doped waveguide amplifiers (EDWAs) are able to offer attractive performance metrics that can exceed SOA-based amplification solutions in traditional single and multi-channel systems. In this letter, we experimentally demonstrate a record high 8 × 40 Gbps non return to zero (NRZ) wavelength division multiplexing (WDM) data amplification through a 5.9 cm long on-chip amplifier consisting of an erbium-doped aluminum oxide spiral waveguide monolithically integrated on the Si3N4 platform. Experimental results show more than 12.7 dB amplification per channel for low saturation total input power of -2.75 dBm, and clear eye diagrams and bit-error rate values below the KR4-FEC limit of 2 × 10-5 for all eight channels without any digital signal processing (DSP) applied to the signal to the receiver or transmitter side. The high losses from the fiber to chip interfaces, however, prevented achieving device net gain