2024 New's Items

MOSFET Probabilistic-Bit Behavior

Tatum LP
Kong X
Stojanovic V
Liu TJK
2024
Probabilistic computing is a physics-based beyond-von-Neumann framework proposed to meet the high energy-efficiency and performance demands of modern AI and combinatorial optimization problems [1] . A probabilistic computing platform is a control loop made up of probabilistic-bits (p-bits), which are essentially tunable random-number-generators (RNGs) [2] , and classical circuitry that updates the p-bit inputs ( Fig. 1a ). When a p-bit’s input is high, it is usually “1”, and when a p-bit’s input is low, it is usually “0” ( Fig. 1b ); in-between is a stochastic region wherein the probability...

Advanced Ferroelectric Modeling for BEOL Negative Capacitance Nanoelectromechanical Switches

Collin Finnan
Lars Tatum
Tsu-Jae King Liu
2024
Negative capacitance (NC) - achieved by adding a ferroelectric layer in series with the dielectric layer (air gap) of an electrostatic actuator - has been proposed as a means of reducing the pull-in voltage of a nano-electro-mechanical (NEM) switch without physically scaling down the gap size. This paper introduces a two-dimensional device simulation framework for NC NEM switches using the ferroelectric material hafnium zirconium oxide. The ferroelectric layer is simulated using both a simplified single polarization domain model and two different multi-domain models. While a dramatic...

Ultrafast optical control of charge orders in kagome metals

Yu-Ping Lin
Vidya Madhavan
Joel E Moore
2024

We show that ultrafast optical pump pulses provide effective control over charge orders in the kagome metals AV3Sb5 with A = K, Rb, and Cs. Starting from the real charge density waves (rCDWs) at the p-type Van Hove singularity, we conduct a thorough analysis of the post-pump dynamics by time-dependent Hartree-Fock theory. Our analysis uncovers distinct dynamical phenomena under linearly and circularly polarized pumps. Linearly polarized pumps induce directional preferences in the rCDWs, accompanied by an enhancement in the flat band. Unexpectedly, charge nematicity also emerges and...

Coherent Magneto-Conductance Oscillations in Amorphous Topological Insulator Nanowires

Siddhant Mal
Elizabeth J Dresselhaus
Joel E Moore
2024
Recent experiments on amorphous materials have established the existence of surface states similar to those of crystalline three-dimensional topological insulators (TIs). Amorphous topological insulators are also independently of interest for thermo-electric and other properties. To develop an understanding of transport in these systems, we carry out quantum transport calculations for a tight-binding model of an amorphous nano-wire pierced by an axial magnetic flux, then compare the results to known features in the case of crystalline models with disorder. Our calculations complement previous...

Crystallography, Group Cohomology, and Lieb-Schultz-Mattis Constraints

Chunxiao Liu
Weicheng Ye
2024
We compute the mod-2 cohomology ring for three-dimensional (3D) space groups and establish a connection between them and the lattice structure of crystals with space group symmetry. This connection allows us to obtain a complete set of Lieb-Schultz-Mattis constraints, specifying the conditions under which a unique, symmetric, gapped ground state cannot exist in 3D lattice magnets. We associate each of these constraints with an element in the third mod-2 cohomology of the space group, when the internal symmetry acts on-site and its projective representations are classified by powers of . We...

Spin-liquid-based topological qubits

Klocke, K.
Liu, Y.
Halász, G. B.
Alicea, J.
2024
Topological quantum computation relies on control of non-Abelian anyons for inherently fault-tolerant storage and processing of quantum information. By now, blueprints for topological qubits are well developed for electrically active topological superconductor and fractional quantum Hall platforms. We leverage recent insights into the creation and detection of non-Abelian anyons in electrically insulating spin systems to propose topological qubit architectures based on quantum spin liquids. We present two types of prototype designs that enable the requisite control in a potentially scalable...

Post-measurement Quantum Monte Carlo

Baweja, K.
Luitz, D. J.
Garratt, S. J.
2024

We show how the effects of large numbers of measurements on many-body quantum ground and thermal states can be studied using Quantum Monte Carlo (QMC). Density matrices generated by measurement in this setting feature products of many local nonunitary operators, and by expanding these density matrices as sums over operator strings we arrive at a generalized stochastic series expansion (SSE). Our `post-measurement SSE' is based on importance sampling of operator strings contributing to a measured thermal density matrix. We demonstrate our algorithm by probing the effects of...

Quantum resource-theoretical analysis of the role of vibrational structure in photoisomerization

Tiwary, S.
Spaventa, G.
Huelga, S. F.
Plenio, M. B.
2024

Thermodynamical systems at the nanoscale, such as single molecules interacting with highly structured vibrational environments, typically undergo non-equilibrium physical processes that lack precise microscopic descriptions. Photoisomerization is such an example which has emerged as a platform on which to study single-molecule ultrafast photochemical processes from a quantum resource theoretic perspective. However, upper bounds on its efficiency have only been obtained under significant simplifications that make the mathematics of the resource-theoretical treatment manageable. Here we...

The multi-state geometry of shift current and polarization

Avdoshkin, A.
Mitscherling, J.
Moore, J. E.
2024

The quantum metric and Berry curvature capture essential properties of non-trivial Bloch states and underpin many fascinating phenomena. However, it becomes increasingly evident that a more comprehensive understanding of quantum state geometry is necessary to explain properties involving Bloch states of multiple bands, such as optical transitions. To this end, we employ quantum state projectors to develop an explicitly gauge-invariant formalism and demonstrate its power with applications to non-linear optics and the theory of electronic polarization. We provide a simple expression...

Quasiperiodicity protects quantized transport in disordered systems without gaps

Gottlob, E.
Borgnia, D. S.
Slager, R.-J.
Schneider, U.
2024
The robustness of topological properties, such as quantized currents, generally depends on the existence of gaps surrounding the relevant energy levels or on symmetry-forbidden transitions. Here, we observe quantized currents that survive the addition of bounded local disorder beyond the closing of the relevant instantaneous energy gaps in a driven Aubry-Andr\'e-Harper chain, a prototypical model of quasiperiodic systems. We explain the robustness using a local picture in \textit{configuration-space} based on Landau-Zener transitions, which rests on the Anderson localisation of the...