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1. Thermal disruption of a Luttinger liquid

   https://doi.org/10.1038/s41467-023-38767-0  

   Cavazos-Cavazos, Danyel; Senaratne, Ruwan; Kafle, Aashish; Hulet, Randall G. (May 2023, Nature Communications)

   Abstract The Tomonaga–Luttinger liquid (TLL) theory describes the low-energy excitations of strongly correlated one-dimensional (1D) fermions. In the past years, a number of studies have provided a detailed understanding of this universality class. More recently, theoretical investigations that go beyond the standard low-temperature, linear-response TLL regime have been developed. While these provide a basis for understanding the dynamics of the spin-incoherent Luttinger liquid, there are few experimental investigations in this regime. Here we report the observation of a thermally induced, spin-incoherent Luttinger liquid in a⁶Li atomic Fermi gas confined to 1D. We use Bragg spectroscopy to measure the suppression of spin-charge separation and the decay of correlations as the temperature is increased. Our results probe the crossover between the coherent and incoherent regimes of the Luttinger liquid and elucidate the roles of the charge and the spin degrees of freedom in this regime. 

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2. Generalized effective spin-chain formalism for strongly interacting spinor gases in optical lattices

   https://doi.org/10.1103/PhysRevA.108.063315  

   Basak, Sagarika; Pu, Han (December 2023, Physical Review A)

   A generalized effective spin-chain model is developed for studies of strongly interacting spinor gases in a one-dimensional (1D) optical lattice. The spinor gas is mapped to a system of spinless fermions and a spin chain. A generalized effective spin-chain Hamiltonian that acts on the mapped system is developed to study the static and dynamic properties of the spinor gas. This provides a computationally efficient alternative tool to study strongly interacting spinor gases in 1D lattice systems. This formalism permits the study of spinor gases with arbitrary spin and statistics, providing a generalized approach for 1D strongly interacting gases. By virtue of its simplicity, it provides an easier tool to study and gain deeper insights into the system. In combination with the model defined previously for continuum systems, a unified framework is developed. Studying the mapped system using this formalism recreates the physics of spinor gas in 1D lattice. Additionally, the time evolution of a quenched system is studied. The generalized effective spin-chain formalism has potential applications in the study of a multitude of interesting phenomena arising in lattice systems such as high-Tc superconductivity and the spin-coherent and spin-incoherent Luttinger liquid regimes. 

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3. An adaptive variational algorithm for exact molecular simulations on a quantum computer

   https://doi.org/10.1038/s41467-019-10988-2  

   Grimsley, Harper R.; Economou, Sophia E.; Barnes, Edwin; Mayhall, Nicholas J. (July 2019, Nature Communications)

   Abstract Quantum simulation of chemical systems is one of the most promising near-term applications of quantum computers. The variational quantum eigensolver, a leading algorithm for molecular simulations on quantum hardware, has a serious limitation in that it typically relies on a pre-selected wavefunction ansatz that results in approximate wavefunctions and energies. Here we present an arbitrarily accurate variational algorithm that, instead of fixing an ansatz upfront, grows it systematically one operator at a time in a way dictated by the molecule being simulated. This generates an ansatz with a small number of parameters, leading to shallow-depth circuits. We present numerical simulations, including for a prototypical strongly correlated molecule, which show that our algorithm performs much better than a unitary coupled cluster approach, in terms of both circuit depth and chemical accuracy. Our results highlight the potential of our adaptive algorithm for exact simulations with present-day and near-term quantum hardware. 

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4. Observation of dynamical fermionization

   https://doi.org/10.1126/science.aaz0242  

   Wilson, Joshua M.; Malvania, Neel; Le, Yuan; Zhang, Yicheng; Rigol, Marcos; Weiss, David S. (March 2020, Science)

   The wave function of a Tonks-Girardeau (T-G) gas of strongly interacting bosons in one dimension maps onto the absolute value of the wave function of a noninteracting Fermi gas. Although this fermionization makes many aspects of the two gases identical, their equilibrium momentum distributions are quite different. We observed dynamical fermionization, where the momentum distribution of a T-G gas evolves from bosonic to fermionic after its axial confinement is removed. The asymptotic momentum distribution after expansion in one dimension is the distribution of rapidities, which are the conserved quantities associated with many-body integrable systems. Our measurements agree well with T-G gas theory. We also studied momentum evolution after the trap depth is suddenly changed to a new nonzero value, and we observed the theoretically predicted bosonic-fermionic oscillations. 

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5. Spin effect on the low-temperature resistivity maximum in a strongly interacting 2D electron system

   https://doi.org/10.1038/s41598-022-09034-x  

   Shashkin, A. A.; Melnikov, M. Yu.; Dolgopolov, V. T.; Radonjić, M. M.; Dobrosavljević, V.; Huang, S.-H.; Liu, C. W.; Zhu, Amy Y.; Kravchenko, S. V. (December 2022, Scientific Reports)

   Abstract The increase in the resistivity with decreasing temperature followed by a drop by more than one order of magnitude is observed on the metallic side near the zero-magnetic-field metal-insulator transition in a strongly interacting two-dimensional electron system in ultra-clean SiGe/Si/SiGe quantum wells. We find that the temperature $$T_{\text {max}}$$ T max , at which the resistivity exhibits a maximum, is close to the renormalized Fermi temperature. However, rather than increasing along with the Fermi temperature, the value $$T_{\text {max}}$$ T max decreases appreciably for spinless electrons in spin-polarizing (parallel) magnetic fields. The observed behaviour of $$T_{\text {max}}$$ T max cannot be described by existing theories. The results indicate the spin-related origin of the effect. 

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