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1. Dynamics for the Haldane phase in the Bilinear-Biquadratic Model

   Arya Dhar, Daniel Jaschke ( February 2021 , ArXivorg)

   null (Ed.)

   The BBM is a promising candidate to study spin-one systems and to design quantum simulators based on its underlying Hamiltonian. The variety of different phases contains amongst other valuable and exotic phases the Haldane phase. We study the Kibble-Zurek physics of linear quenches into the Haldane phase. We outline ideal quench protocols to minimize defects in the final state while exploiting different linear quench protocols via the uniaxial or interaction term. Furthermore, we look at the fate of the string order when quenching from a topologically non-trivial phase to a trivial phase. Our studies show this depends significantly on the path chosen for quenching; for example, we discover quenches from \Neel{} to Haldane phase which reach a string order greater than their ground state counterparts for the initial or final state at intermediate quench times. 

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2. Optically addressable molecular spins for quantum information processing

   https://doi.org/10.1126/science.abb9352  

   Bayliss, S. L. ; Laorenza, D. W. ; Mintun, P. J. ; Kovos, B. D. ; Freedman, D. E. ; Awschalom, D. D. ( November 2020 , Science)

   Spin-bearing molecules are promising building blocks for quantum technologies as they can be chemically tuned, assembled into scalable arrays, and readily incorporated into diverse device architectures. In molecular systems, optically addressing ground-state spins would enable a wide range of applications in quantum information science, as has been demonstrated for solid-state defects. However, this important functionality has remained elusive for molecules. Here, we demonstrate such optical addressability in a series of synthesized organometallic, chromium(IV) molecules. These compounds display a ground-state spin that can be initialized and read out using light and coherently manipulated with microwaves. In addition, through atomistic modification of the molecular structure, we vary the spin and optical properties of these compounds, indicating promise for designer quantum systems synthesized from the bottom-up.

    

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3. Spectral Gaps and Incompressibility in a $${\varvec{\nu }}$$ = 1/3 Fractional Quantum Hall System

   https://doi.org/10.1007/s00220-021-03997-0  

   Nachtergaele, Bruno ; Warzel, Simone ; Young, Amanda ( April 2021 , Communications in Mathematical Physics)

   null (Ed.)

   Abstract We study an effective Hamiltonian for the standard $$\nu =1/3$$ ν = 1 / 3 fractional quantum Hall system in the thin cylinder regime. We give a complete description of its ground state space in terms of what we call Fragmented Matrix Product States, which are labeled by a certain family of tilings of the one-dimensional lattice. We then prove that the model has a spectral gap above the ground states for a range of coupling constants that includes physical values. As a consequence of the gap we establish the incompressibility of the fractional quantum Hall states. We also show that all the ground states labeled by a tiling have a finite correlation length, for which we give an upper bound. We demonstrate by example, however, that not all superpositions of tiling states have exponential decay of correlations. 

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4. Unveiling Operator Growth Using Spin Correlation Functions

   https://doi.org/10.3390/e23050587  

   Carrega, Matteo ; Kim, Joonho ; Rosa, Dario ( May 2021 , Entropy)

   null (Ed.)

   In this paper, we study non-equilibrium dynamics induced by a sudden quench of strongly correlated Hamiltonians with all-to-all interactions. By relying on a Sachdev-Ye-Kitaev (SYK)-based quench protocol, we show that the time evolution of simple spin-spin correlation functions is highly sensitive to the degree of k-locality of the corresponding operators, once an appropriate set of fundamental fields is identified. By tracking the time-evolution of specific spin-spin correlation functions and their decay, we argue that it is possible to distinguish between operator-hopping and operator growth dynamics; the latter being a hallmark of quantum chaos in many-body quantum systems. Such an observation, in turn, could constitute a promising tool to probe the emergence of chaotic behavior, rather accessible in state-of-the-art quench setups. 

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5. Charge order textures induced by non-linear couplings in a half-doped manganite

   https://doi.org/10.1038/s41467-021-24026-7  

   El Baggari, Ismail ; Baek, David J. ; Zachman, Michael J. ; Lu, Di ; Hikita, Yasuyuki ; Hwang, Harold Y. ; Nowadnick, Elizabeth A. ; Kourkoutis, Lena F. ( June 2021 , Nature Communications)

   The self-organization of strongly interacting electrons into superlattice structures underlies the properties of many quantum materials. How these electrons arrange within the superlattice dictates what symmetries are broken and what ground states are stabilized. Here we show that cryogenic scanning transmission electron microscopy (cryo-STEM) enables direct mapping of local symmetries and order at the intra-unit-cell level in the model charge-ordered system Nd_1/2Sr_1/2MnO₃. In addition to imaging the prototypical site-centered charge order, we discover the nanoscale coexistence of an exotic intermediate state which mixes site and bond order and breaks inversion symmetry. We further show that nonlinear coupling of distinct lattice modes controls the selection between competing ground states. The results demonstrate the importance of lattice coupling for understanding and manipulating the character of electronic self-organization and that cryo-STEM can reveal local order in strongly correlated systems at the atomic scale.

    

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