Quantum Spin Puddles and Lakes: NISQ-Era Spin Liquids from Non-Equilibrium Dynamics

While many-body systems can host long-ranged entangled quantum spin liquids (QSLs), the ingredients for realizing these as ground states can be prohibitively difficult. In many circumstances, one requires (i) a constrained Hilbert space and (ii) an extensive quantum superposition. The paradigmatic example is the toric code, or $\mathbb{Z}_2$ spin liquid, which is a superposition of closed loop states. We show how non-equilibrium Hamiltonian dynamics can provide a streamlined route toward creating such QSLs. Rather than cooling into the ground state of a Hamiltonian, we show how a simple parameter sweep can dynamically project a family of initial product states into the constrained space, giving rise to a QSL. For the toric code, this is achieved in systems with a separation in energy scales between the $e$- and $m$-anyons, where one can sweep in a way that is adiabatic (sudden) with respect to the former (latter). Although this separation of scales does not extend to the thermodynamic limit, we analytically and numerically show that this method efficiently prepares a spin liquid in finite-sized regions, which we brand ``quantum spin lakes.'' This mechanism elucidates recent experimental and numerical observations of the dynamical state preparation of the ruby lattice spin liquid in Rydberg atom arrays. In fact, the slow dynamics of $m$-anyons suggest that we can capture spin lake preparation by simulating the dynamics on tree lattices, which we confirm with tensor network simulations. Finally, we use this mechanism to propose new experiments, e.g., for preparing a finite-sized $U(1)$ spin liquid as a honeycomb Rokhsar-Kivelson dimer model using Rydberg atoms -- which is remarkable given its equilibrium counterpart is unstable in $2 + 1$D. Our work opens up a new avenue in the study of non-equilibrium physics, as well as the exploration of exotic states of finite extent in NISQ devices.Comment: 24 pages with 9 figures + 5 page supplementary with 7 figure

Emergent Holographic Forces from Tensor Networks and Criticality

The AdS/CFT correspondence stipulates a duality between conformal field theories and certain theories of quantum gravity in one higher spatial dimension. However, probing this conjecture on contemporary classical or quantum computers is challenging. We formulate an efficiently implementable multi-scale entanglement renormalization ansatz (MERA) model of AdS/CFT providing a mapping between a (1+1)-dimensional critical spin system and a (2+1)-dimensional bulk theory. Using a combination of numerics and analytics, we show that the bulk theory arising from this optimized tensor network furnishes excitations with attractive interactions. Remarkably, these excitations have one- and two-particle energies matching the predictions for matter coupled to AdS gravity at long distances, thus displaying key features of AdS physics. We show that these potentials arise as a direct consequence of entanglement renormalization and discuss how this approach can be used to efficiently simulate bulk dynamics using realistic quantum devices.Comment: 7+23 pages, 15 figure

Putting the Law in its Place: Analyses of recent developments in law relating to same-sex desire in India and Uganda

This collection of essays has been jointly produced by Sexuality Policy Watch and the IDS Sexuality and Development Programme. The collection of analyses presented here juxtaposes the Indian and the Ugandan contexts with the intention of opening up new questions for struggles in both these places, but also with the objective of generating a deeper conversation amongst activists and academics about the peculiarities of Law and Politics as distinct (if connected) realms of action. One feature of these various essays is to bring about the circulation of more nuanced analyses of the particular political-economic and cultural conditions for these dramatic developments in law , which take place at the intricate intersections between global economics, national politics and the so called ‘return of the religious’ (Derrida, 1998) in dogmatic manifestations. Another aspect examined by some of the authors regards the limitations and caveats of dominant juridical, economic and scientific rationales that currently pervade political struggles and advocacy in relation to human rights

Superconductivity in a Topological Lattice Model with Strong Repulsion

The highly tunable nature of synthetic quantum materials -- both in the solid-state and cold atom contexts -- invites examining which microscopic ingredients aid in the realization of correlated phases of matter such as superconductors. Recent experimental advances in moir\'e materials suggest that unifying the features of the Fermi-Hubbard model and quantum Hall systems creates a fertile ground for the emergence of such phases. Here, we introduce a minimal 2D lattice model that incorporates exactly these features: time-reversal symmetry, band topology, and strong repulsive interactions. By using infinite cylinder density matrix renormalization group methods (cylinder iDMRG), we investigate the ground state phase diagram of this model. We find that it hosts an interaction-induced quantum spin Hall (QSH) insulator and demonstrate that weakly hole-doping this state gives rise to a superconductor at a finite circumference, with indications that this behavior persists on larger cylinders. At the aforementioned circumference, the superconducting phase is surprisingly robust to perturbations including additional repulsive interactions in the pairing channel. By developing a technique to probe the superconducting gap function in iDMRG, we phenomenologically characterize the superconductor. Namely, we demonstrate that it is formed from the weak pairing of holes atop the QSH insulator. Furthermore, we determine the pairing symmetry of the superconductor, finding it to be $p$-wave -- reminiscent of the unconventional superconductivity reported in experiments on twisted bilayer graphene (TBG). Motivated by this, we elucidate structural similarities and differences between our model and those of TBG in its chiral limit. Finally, to provide a more direct experimental realization, we detail an implementation of our Hamiltonian in a system of cold fermionic alkaline-earth atoms in an optical lattice.Comment: 27 pages (with 8 figures) + 35 pages supplementary (with 14 figures

Framework to Improve Labour Productivity for Indian Building Projects

This study explores the practice of planning and productivity measurement on Indian building construction sites and suggests a framework to improve the practice. An exploratory study based on observing several projects was initially undertaken and it was found that there was no structured method utilised to analyse and improve productivity during the construction phase. Further analysis of planning practices on 15 building construction projects revealed that while the overall milestone plan was appropriate, the critical path method schedule (macro schedule) had several limitations, which made its relevance for look-ahead planning and coordination of resources questionable. Without an appropriate model for medium term planning, the short-term plans became uncoordinated and resulted in significant wastages. Based on a comparison of observed practices with documented best practices, and constraints unique to projects in India, the gaps in developing CPM based schedule are enumerated and strategies to close the gaps are suggested. In addition to this top-down approach to develop a realistic CPM based schedule, a bottom up approach to monitor the daily progress against the planned weekly targets is proposed. While the conventional monitoring framework mandates this approach, there were several gaps in practice that were observed. The causes for these gaps are analysed and suggestions to close the gaps are proposed. The proposed framework consisting of the top-down and bottom-up approach is expected to overcome several of the barriers to measure and improve labour productivity on Indian building projects.International Council for Research and Innovation in Building and Construction (CIB

Measuring the Pull-Off Force of an Individual Fiber Using a Novel Picoindenter/Scanning Electron Microscope Technique

We employed a novel picoindenter (PI)/scanning electron microscopy (SEM) technique to measure the pull-off force of an individual electrospun poly(vinylidene fluoride) (PVDF) fibers. Individual fibers were deposited over a channel in a custom-designed silicon substrate, which was then attached to a picoindenter. The picoindenter was then positioned firmly on the sample stage of the SEM. The picoindenter tip laterally pushed individual fibers to measure the force required to detach it from the surface of substrate. SEM was used to visualize and document the process. The measured pull-off force ranged between 5.8 ± 0.2 μN to ~17.8 ± 0.2 μN for individual fibers with average diameter ranging from 0.8 to 2.3 μm. Thus, this study, a first of its kind, demonstrates the use of a picoindenter to measure the pull-off force of a single micro/nanofiber