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Observation of antiferromagnetic correlations in an ultracold SU(N) Hubbard model


Mott insulators are paradigmatic examples of strongly correlated physics from which many phases of quantum matter with hard-to-explain properties emerge. Extending the typical SU(2) spin symmetry of Mott insulators to SU(N) is predicted to produce exotic quantum magnetism at low temperatures. In this work, we experimentally observe nearest-neighbour spin correlations in a SU(6) Hubbard model realized by ytterbium atoms in optical lattices. We study one-dimensional, two-dimensional square and three-dimensional cubic lattice geometries. The measured SU(6) spin correlations are enhanced compared with the SU(2) correlations, owing to strong Pomeranchuk cooling. The experimental data for a one-dimensional lattice agree qualitatively with our theoretical calculations, with an error of at most 30%, without any fitting parameters. Detailed comparison between theory and experiment allows us to infer the temperature to be the lowest achieved for a cold-atom Fermi–Hubbard model. For three-dimensional lattices, the experiments reach entropies below the regime where our calculations converge, highlighting the importance of these experiments as quantum simulations.

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Fig. 1: Experimental setup.
Fig. 2: Entropy dependence of the nearest-neighbour correlations of the SU(N) FHM at U/t = 15.3.
Fig. 3: Dimension dependence of the spin correlations.

Data availability

All the data presented in this paper are available from the corresponding author upon reasonable request.

Code availability

The mathematical codes that support the findings of the study are available from the corresponding author upon reasonable request.


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We thank H. Ozawa for contributions in the early stage of the experiment. The experimental work was supported by JSPS grants-in-aid for scientific research nos. JP17H06138, JP18H05405 and JP18H05228, the Impulsing Paradigm Change through Disruptive Technologies (ImPACT) programme, JST CREST (no. JPMJCR1673) and MEXT Quantum Leap Flagship Program (MEXT Q-LEAP) grant no. JPMXS0118069021. Y. K. acknowledges the support of the Grant-in-Aid for JSPS Fellows (no. 17J00486). The work of K.R.A.H., E.I.-G.-P. and H.-T.W. was supported in part by the Welch Foundation through grant no. C1872 and the National Science Foundation through grant no. PHY1848304. The work of R.T.S. was supported by grant DE-SC0014671 funded by the U.S. Department of Energy Office of Science.

Author information

Authors and Affiliations



S.T., N.N. and Y. Takasu carried out experiments. S.T. analysed the data. Y.K. gave advice on experiments from the theoretical viewpoint. Y. Takahashi conducted the whole experiment. E.I.-G.-P. developed the SU(N) DQMC code extended from R.T.S.’s SU(2) code, performed the DQMC calculations, many ED calculations and the LDA calculations with ED and DQMC results, and carried out the theoretical data analysis. H.-T.W. developed the ED code and performed many of the ED calculations. R.T.S. and K.R.A.H. conceived and supervised the theoretical calculations. E.I.-G.-P., H.-T.W., R.T.S. and K.R.A.H. all contributed to interpreting the theory and theory–experiment comparisons. All the authors contributed to preparing the manuscript. S.T. and E.I.-G.-P. contributed equally to this work.

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Correspondence to Shintaro Taie.

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Nature Physics thanks Peter Schauß and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1 Temperature of a 1D SU(6) Fermi gas at U/t = 15.3.

The vertical dashed lines indicate the range of the largest experimentally measured STO imbalance in 1D that is consistent with error bars. The temperature of this datapoint is inferred from the finite-size scaling curves and the results are summarized in panel (d). The fss error is a conservative estimate of the finite-size error, the difference between the finite-size scaled results and the L = 8 site chain. The exp error comes from the experimental uncertainty on the correlations.

Extended Data Fig. 2 Interaction dependence of the nearest neighbor correlations.

Behavior of (a) STO amplitude and (b) singlet-triplet imbalance in 1D and 3D lattices are shown. Experimental data is shown for SU(6) systems with initial entropy S/NptclkB = 1.4 ± 0.1. The error bars are extracted from the error of fit in the analysis of the STO signal. Solid lines are the result of exact diagonalization calculations for S/NptclkB = 1.4, and the error bars correspond to the sum in quadrature of the finite-size error and the basis-state truncation error. The inset presents the entropy per particle extracted by fitting it to reproduce the experimentally measured spin correlations. Results saturate at S/NptclkB = 1.818 ± 0.005. Error bars in the inset come from the experimental uncertainty on the correlations.

Extended Data Fig. 3 Normalized STO amplitude for an SU(6) Fermi gas in an L = 5 site chain with U/t = 15.3 for different truncations of the Hilbert space.

Basis states with an on-site energy larger than the energy cutoff Ecut, as well as those that exceed the maximum particle number \({N}_{\max }\) are disregarded. There is no visible difference between calculations. The inset shows the absolute value of the difference between the \({E}_{{{{\rm{cut}}}}}=2U,{N}_{\max }=7\) and \({E}_{{{{\rm{cut}}}}}=U,{N}_{\max }=5\) curves.

Extended Data Fig. 4 Trap anharmonicity.

(a) Full external potential (optical + gravity) profile along the direction of gravity z. The shaded region is excluded from the calculation of DOS. (b) Density of states calculated from the external potential for the 3D cubic geometry. The corresponding harmonic approximation is also shown. The atoms are sensitive only to the density of states for E/t 10.

Extended Data Fig. 5 Finite-size scaling in 1D.

Normalized STO amplitude and imbalance for SU(2) and SU(6) Fermi gases in L-site chains and the results after finite-size scaling (fss) for U/t = 15.3. The inset in panel (b) illustrates the finite-size scaling procedure.

Extended Data Table 1 Error estimates for the DQMC calculation at U/t = 15.3.

Errors are presented at kBT/t = 1. Most errors decrease with increasing temperature. The top two rows estimate errors by considering homogeneous systems as follows: “Finite Tcut” is the error by a non-infinite value of Tcut in entropy integrations estimated by the difference of kBTcut = 1000 and 500. “Statistical” estimates is the standard error of the mean, taken at its largest value over all μ and T considered. The bottom 5 rows come from results after adiabatic loading in the trap, as follows. “Finite size (2D)” is the finite-size error estimated by the difference between A(S) in 44 and 66 geometries, “Trotter-step” is the Trotter error estimated by the difference of A(S) for Trotter step size Δμ = 0.05 and 0.025, “μ-grid coarseness” and “T-grid coarseness” are the estimates of the errors associated with discretizing μ and T by taking the difference of the result after doubling the grid spacing, and “Statistical (adiabatic loading)” is the standard error of the mean of the DQMC.

Extended Data Table 2 Error estimates for the different error sources involved in the DQMC calculation for U/t = 8 and N = 3.

Row labels are the same as in Extended Data Table 1. The first three rows are for homogeneous systems while the last is for the A(S) after adiabatic loading. For homogeneous system results, we report the largest error in the whole range of temperatures/entropies considered. The T grid coarseness error for S vs T monotonically increases from 2.0 × 10−2 at kBT/t = 0.64 to the value reported in the table, 1.3 × 10−1, at kBT/t = 4.

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Taie, S., Ibarra-García-Padilla, E., Nishizawa, N. et al. Observation of antiferromagnetic correlations in an ultracold SU(N) Hubbard model. Nat. Phys. (2022).

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