Spin decoupling and line narrowing are observed for the first time in an optical transition, $^{3}H_{4}\ensuremath{\leftrightarrow}^{1}D_{2}$ of ${\mathrm{Pr}}^{3+}$ in La ${\mathrm{F}}_{3}$ at 2\ifmmode^\circ\else\textdegree\fi{}K, with use of optical free-induction decay. The $^{19}\mathrm{F}$ nuclei, when irradiated by an appropriate rf field, undergo forced precession about an effective field at the magic angle in the rotating frame. The fluctuating $^{19}\mathrm{F}$ - $^{19}\mathrm{F}$ dipolar interaction is thereby quenched and the optical linewidth drops from \ensuremath{\sim}10 to \ensuremath{\sim}2 kHz, as predicted in a theory of spin diffusion.Spin decoupling and line narrowing are observed for the first time in an optical transition, $^{3}H_{4}\ensuremath{\leftrightarrow}^{1}D_{2}$ of ${\mathrm{Pr}}^{3+}$ in La${\mathrm{F}}_{3}$ at 2\ifmmode^\circ\else\textdegree\fi{}K, with use of optical free-induction decay. The $^{19}\mathrm{F}$ nuclei, when irradiated by an appropriate rf field, undergo forced precession about an effective field at the magic angle in the rotating frame. The fluctuating $^{19}\mathrm{F}$-$^{19}\mathrm{F}$ dipolar interaction is thereby quenched and the optical linewidth drops from \ensuremath{\sim}10 to \ensuremath{\sim}2 kHz, as predicted in a theory of spin diffusion.

Physical Review LettersDec 17, 197966 citations

Optical Correlation Phenomena

Jan Peřina

Springer eBooksJan 1, 19840 citations

Optical Correlation Phenomena

Jan Peřina

Springer eBooksJan 1, 19910 citations

Quantum computation based on magic-angle-spinning solid state nuclear magnetic resonance spectroscopy

Shangwu Ding, CHARLES A. MCDOWELL, Chaohui Ye +6 more

arXiv:quant-ph/0110014The European Physical Journal BNov 1, 20014 citations

Correlation effects in magic-angle twisted bilayer graphene: An auxiliary-field quantum Monte Carlo study

Zhi-Yu Xiao, Shiwei Zhang

Magic-angle twisted bilayer graphene (MATBG) presents a fascinating platform for investigating the effects of electron interactions in topological flat bands. The Bistritzer-MacDonald (BM) model provides a simplified quantitative description of the flat bands. Introducing long-range Coulomb interactions leads to an interacting BM (IBM) Hamiltonian, a momentum-space continuum description which offers a very natural starting point for many-body studies of MATBG. Accurate and reliable many-body computations in the IBM model are challenging, however, and have been limited mostly to special fillings or smaller lattice sizes. We employ a state-of-the-art auxiliary-field quantum Monte Carlo (AFQMC) method to study the IBM model, which constrains the sign problem to enable accurate treatment of large system sizes. We determine ground-state properties and quantify errors compared to mean-field theory calculations. Our calculations identify correlated metal states and their competition with the insulating Kramers intervalley-coherent state at both half-filling and charge neutrality. Additionally, we investigate one- and three-quarter fillings, and examine the effect of many-body corrections beyond single Slater determinant solutions. We discuss the effect that details of the IBM Hamiltonian have on the results, including different forms of double-counting corrections, and the need to establish and precisely specify many-body Hamiltonians to allow more direct and quantitative comparisons with experiments in MATBG.Magic-angle twisted bilayer graphene (MATBG) presents a fascinating platform for investigating the effects of electron interactions in topological flat bands. The Bistritzer-MacDonald (BM) model provides a simplified quantitative description of the flat bands. Introducing long-range Coulomb interactions leads to an interacting BM (IBM) Hamiltonian, a momentum-space continuum description which offers a very natural starting point for many-body studies of MATBG. Accurate and reliable many-body computations in the IBM model are challenging, however, and have been limited mostly to special fillings or smaller lattice sizes. We employ a state-of-the-art auxiliary-field quantum Monte Carlo (AFQMC) method to study the IBM model, which constrains the sign problem to enable accurate treatment of large system sizes. We determine ground-state properties and quantify errors compared to mean-field theory calculations. Our calculations identify correlated metal states and their competition with the insulating Kramers intervalley-coherent state at both half-filling and charge neutrality. Additionally, we investigate one- and three-quarter fillings, and examine the effect of many-body corrections beyond single Slater determinant solutions. We discuss the effect that details of the IBM Hamiltonian have on the results, including different forms of double-counting corrections, and the need to establish and precisely specify many-body Hamiltonians to allow more direct and quantitative comparisons with experiments in MATBG.

arXiv:2405.17808Physical Review ResearchJan 27, 20253 citations

Spin decoupling and line narrowing are observed for the first time in an optical transition, $^{3}H_{4}\ensuremath{\leftrightarrow}^{1}D_{2}$ of

{\mathrm{Pr}}^{3+}

in La

{\mathrm{F}}_{3}

at 2\ifmmode^\circ\else\textdegree\fi{}K, with use of optical free-induction decay. The

^{19}\mathrm{F}

nuclei, when irradiated by an appropriate rf field, undergo forced precession about an effective field at the magic angle in the rotating frame. The fluctuating

^{19}\mathrm{F}

^{19}\mathrm{F}

dipolar interaction is thereby quenched and the optical linewidth drops from \ensuremath{\sim}10 to \ensuremath{\sim}2 kHz, as predicted in a theory of spin diffusion.