2024 New's Items

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...

Entanglement dynamics in monitored Kitaev circuits: loop models, symmetry classification, and quantum Lifshitz scaling

Klocke, K.
Simm, D.
Zhu, G.-Y.
Trebst, S.
Buchhold, M.
2024

Quantum circuits offer a versatile platform for simulating digital quantum dynamics and uncovering novel states of non-equilibrium quantum matter. One principal example are measurement-induced phase transitions arising from non-unitary dynamics in monitored circuits, which employ mid-circuit measurements as an essential building block next to standard unitary gates. Although a comprehensive understanding of the dynamics in generic circuits is still evolving, we contend that monitored quantum circuits give rise to robust phases of dynamic matter, which – akin to Hamiltonian ground state...

Spin Excitation Continuum in the Exactly Solvable Triangular-Lattice Spin Liquid CeMgAl11O19

Gao, B.
Chen, T.
Liu, C.
Klemm, M. L.
Zhang, S.
Ma, Z.
Xu, X.
Won, C.
McCandless, G. T.
Murai, N.
Ohira-Kawamura, S.
Moxim, S. J.
Ryan, J. T.
Huang, X.
Wang, X.
Chan, J. Y.
Cheong, S.-W.
Tchernyshyov, O.
Balents, L.
Dai, P.
2024

In magnetically ordered insulators, elementary quasiparticles manifest as spin waves - collective motions of localized magnetic moments propagating through the lattice - observed via inelastic neutron scattering. In effective spin-1/2 systems where geometric frustrations suppress static magnetic order, spin excitation continua can emerge, either from degenerate classical spin ground states or from entangled quantum spins characterized by emergent gauge fields and deconfined fractionalized excitations. Comparing the spin Hamiltonian with theoretical models can unveil the microscopic...

Sublattice polarization from destructive interference on common lattices

Yu-Ping Lin
2024
We show that sublattice-polarized states (SLPSs) appear ubiquitously on the common lattices. We first establish the destructive-interference (DI) scenario for the SLPSs, which is systematized by a point-group-symmetry interpretation. The examples on common one-, two-, and three-dimensional lattices are then demonstrated. We also deduce the symmetry-protected robustness of SLPSs against further-neighbor hoppings. Moreover, the DI scenario can be generalized to the multi-SLP. The important effects on interaction-driven phases are studied by Hartree-Fock analysis.

A tale of two localizations: coexistence of flat bands and Anderson localization in a photonics-inspired amorphous system

Dresselhaus, E. J.
Avdoshkin, A.
Jia, Z.
Secli, M.
Kante, B.
Moore, J. E.
2024
Emerging experimental platforms use amorphousness, a constrained form of disorder, to tailor meta-material properties. We study localization under this type of disorder in a class of models generalizing recent experiments on photonic systems. We explore two kinds of localization that emerge in these models: Anderson localization by disorder, and the existence of compact, macroscopically degenerate localized states as in many crystalline flat bands. We find localization properties to depend on the symmetry class within a family of amorphized kagom\'{e} tight-binding models, set by a tunable...

Machine learning of 27Al NMR quadrupolar tensors for crystalline structures from DFT

Sun, H.
Dwaraknath, S.
West, M. E.
Ling, H.
Persson, K.
Hayes, S.
2024
NMR crystallography has emerged as promising technique for the determination and refinement of crystal structures. The crystal structure of compounds containing quadrupolar nuclei, such as 27Al, can be improved by directly comparing solid-state NMR measurements to DFT computations of the electric field gradient (EFG). The high computational cost of these first-principles calculations limits the applicability of this method to all but the most well-defined structures. We developed a fast, low-cost machine learning model to predict EFG parameters based on local structural motifs and elemental...

Quantum Melting of a Disordered Wigner Solid

Xiang, Z.
Li, H.
Xiao, J.
Naik, M. H.
Ge, Z.
He, Z.
Chen, S.
Nie, J.
Li, S.
Jiang, Y.
Sailus, R.
Banerjee, R.
Taniguchi, T.
Watanabe, K.
Tongay, S.
Louie, S. G.
Crommie, M. F.
Wang, F.
2024

The behavior of two-dimensional electron gas (2DEG) in extreme coupling limits are reasonably well-understood, but our understanding of intermediate region remains limited. Strongly interacting electrons crystalize into a solid phase known as the Wigner crystal at very low densities, and these evolve to a Fermi liquid at high densities. At intermediate densities, however, where the Wigner crystal melts into a strongly correlated electron fluid that is poorly understood partly due to a lack of microscopic probes for delicate quantum phases. Here we report the first imaging of a...