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1. State preparation in a Jaynes-Cummings lattice with quantum optimal control

   https://doi.org/10.1038/s41598-023-47002-1  

   Parajuli, Prabin ; Govindarajan, Anuvetha ; Tian, Lin ( November 2023 , Scientific Reports)

   High-fidelity preparation of quantum states in an interacting many-body system is often hindered by the lack of knowledge of such states and by limited decoherence times. Here, we study a quantum optimal control (QOC) approach for fast generation of quantum ground states in a finite-sized Jaynes-Cummings lattice with unit filling. Our result shows that the QOC approach can generate quantum many-body states with high fidelity when the evolution time is above a threshold time, and it can significantly outperform the adiabatic approach. We study the dependence of the threshold time on the parameter constraints and the connection of the threshold time with the quantum speed limit. We also show that the QOC approach can be robust against control errors. Our result can lead to advances in the application of the QOC to many-body state preparation.

    

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2. Entanglement in the quantum phases of an unfrustrated Rydberg atom array

   https://doi.org/10.1038/s41467-023-41166-0  

   O’Rourke, Matthew J. ; Chan, Garnet Kin-Lic ( September 2023 , Nature Communications)

   Recent experimental advances have stimulated interest in the use of large, two-dimensional arrays of Rydberg atoms as a platform for quantum information processing and to study exotic many-body quantum states. However, the native long-range interactions between the atoms complicate experimental analysis and precise theoretical understanding of these systems. Here we use new tensor network algorithms capable of including all long-range interactions to study the ground state phase diagram of Rydberg atoms in a geometrically unfrustrated square lattice array. We find a greatly altered phase diagram from earlier numerical and experimental studies, revealed by studying the phases on the bulk lattice and their analogs in experiment-sized finite arrays. We further describe a previously unknown region with a nematic phase stabilized by short-range entanglement and an order from disorder mechanism. Broadly our results yield a conceptual guide for future experiments, while our techniques provide a blueprint for converging numerical studies in other lattices.

    

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3. Finite temperature phase transition in a cross-dimensional triangular lattice

   https://doi.org/10.1088/1367-2630/ab2b5f  

   Jin, Shengjie ; Guo, Xinxin ; Peng, Peng ; Chen, Xuzong ; Li, Xiaopeng ; Zhou, Xiaoji ( July 2019 , New Journal of Physics)

   Atomic many-body phase transitions and quantum criticality have recently attracted much attention in non-standard optical lattices. Here we perform an experimental study of finite temperature superfluid transition of bosonic atoms confined in a three dimensional triangular lattice, whose structure can be continuously deformed to dimensional crossover regions including quasi-one and two dimensions. This non-standard lattice system provides a versatile platform to investigate many-body correlated phases. For the three dimensional case, we find that the finite temperature superfluid transition agrees quantitatively with the Gutzwiller mean field theory prediction, whereas tuning towards reduced dimensional cases, both quantum and thermal fluctuation effects are more dramatic, and the experimental measurement for the critical point becomes strongly deviated from the mean field theory. We characterize the fluctuation effects in the whole dimension crossover process. Our experimental results imply strong many-body correlations in the system beyond mean field description, paving a way to study quantum criticality near Mott-superfluid transition in finite temperature dimension-crossover lattices.

    

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4. Efficient pathway to NaCs ground state molecules

   https://doi.org/10.1088/1367-2630/acd411  

   Warner, Claire ; Bigagli, Niccolò ; Lam, Aden Z. ; Yuan, Weijun ; Zhang, Siwei ; Stevenson, Ian ; Will, Sebastian ( June 2023 , New Journal of Physics)

   We present a study of two-photon pathways for the transfer of NaCs molecules to their rovibrational ground state. Starting from NaCs Feshbach molecules, we perform bound-bound excited state spectroscopy in the wavelength range from 900 nm to 940 nm, covering more than 30 vibrational states of the$c^3{\mathrm{\Sigma }}^{+}$,$b^3\mathrm{\Pi }$, and$B^1\mathrm{\Pi }$electronic states. Analyzing the rotational substructure, we identify the highly mixed$c^3{\mathrm{\Sigma }}_1^{+}|v=22⟩\sim b^3{\mathrm{\Pi }}_1|v=54⟩$state as an efficient bridge for stimulated Raman adiabatic passage. We demonstrate transfer into the NaCs ground state with an efficiency of up to 88(4)%. Highly efficient transfer is critical for the realization of many-body quantum phases of strongly dipolar NaCs molecules and high fidelity detection of single molecules, for example, in spin physics experiments in optical lattices and quantum information experiments in optical tweezer arrays.

    

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5. Experimental realization of an extended Fermi-Hubbard model using a 2D lattice of dopant-based quantum dots

   https://doi.org/10.1038/s41467-022-34220-w  

   Wang, Xiqiao ; Khatami, Ehsan ; Fei, Fan ; Wyrick, Jonathan ; Namboodiri, Pradeep ; Kashid, Ranjit ; Rigosi, Albert F. ; Bryant, Garnett ; Silver, Richard ( December 2022 , Nature Communications)

   Abstract The Hubbard model is an essential tool for understanding many-body physics in condensed matter systems. Artificial lattices of dopants in silicon are a promising method for the analog quantum simulation of extended Fermi-Hubbard Hamiltonians in the strong interaction regime. However, complex atom-based device fabrication requirements have meant emulating a tunable two-dimensional Fermi-Hubbard Hamiltonian in silicon has not been achieved. Here, we fabricate 3 × 3 arrays of single/few-dopant quantum dots with finite disorder and demonstrate tuning of the electron ensemble using gates and probe the many-body states using quantum transport measurements. By controlling the lattice constants, we tune the hopping amplitude and long-range interactions and observe the finite-size analogue of a transition from metallic to Mott insulating behavior. We simulate thermally activated hopping and Hubbard band formation using increased temperatures. As atomically precise fabrication continues to improve, these results enable a new class of engineered artificial lattices to simulate interactive fermionic models. 

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