Abstract
Discontinuous (first-order) quantum phase transitions and the associated metastability play central roles in diverse areas of physics, ranging from ferromagnetism to the false-vacuum decay in the early Universe1,2; yet, their dynamics are not well understood. Ultracold atoms provide an ideal platform for experimental simulations of quantum phase transitions3,4; so far, however, studies of first-order phase transitions have been limited to systems with weak interactions5,6,7,8, where quantum effects are exponentially suppressed. Here we realize a strongly correlated driven many-body system whose transition can be tuned from continuous to discontinuous. Resonant shaking of a one-dimensional optical lattice hybridizes the two lowest Bloch bands9,10, driving a novel transition from a Mott insulator to a superfluid with a staggered phase order. For weak shaking amplitudes, this transition is discontinuous and the system can remain frozen in a metastable state, whereas for strong shaking, it undergoes a continuous transition towards a superfluid. Our observations of this metastability and hysteresis agree with numerical simulations and pave the way for exploring the crucial role of quantum fluctuations in discontinuous transitions.
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Data availability
The data for all figures that support the findings of this study are available in Hierarchical Data Format (HDF5) at the Apollo repository (https://doi.org/10.17863/CAM.78025)
Code availability
The code that supports the plots in this paper is available from the corresponding author upon reasonable request.
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Acknowledgements
This work was partly funded by the European Commission ERC Starting Grant QUASICRYSTAL, the EPSRC Grant EP/R044627/1 and Programme Grant DesOEQ (EP/P009565/1), and by a Simons Investigator Award. We are grateful to E. Gottlob and A. Eckardt for fruitful discussions.
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N.C. and U.S. conceived and supervised the project, with S.D. and B.S. leading the detailed design. B.S., S.B., J.-C.Y. and E.C. performed the experiments. B.S. analysed the experimental data and S.D. performed the numerical simulations. All the authors contributed to the interpretation of the results and writing of the manuscript.
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Extended data
Extended Data Fig. 1 Single-particle correlations.
a, Average correlations \(\langle \langle {\hat{a}}_{i}^{{\dagger} }{\hat{a}}_{i+r}\rangle \rangle\) and \(| \langle \langle {\hat{b}}_{i}^{{\dagger} }{\hat{b}}_{i+r}\rangle \rangle |\) in the ground state with L = 64 sites, fitted with an exponential times a power law. b-c, Correlation length (solid lines) and Luttinger parameter (dashed lines) extracted from the fits across first-order and continuous transitions denoted by vertical lines (cf. Extended Data Fig. 2).
Extended Data Fig. 2 Entanglement and central charge.
a, Von Neumann entanglement entropy across bipartitions of the ground state for L = 64 and \({{{\mathcal{A}}}}=3\) nm with different shaking frequencies, fitted with the conformal field theory (CFT) prediction in Eq. (10). b-f, Fitted central charge c as a function of the shaking frequency at increasing shaking amplitudes, exhibiting discontinuous jumps and smooth peaks characteristic of discontinuous (first-order) and continuous phase transitions, respectively (shown by the vertical dashed lines, with the same color convention as in the phase diagram in Supplementary Fig. S3).
Extended Data Fig. 3 Frequency modulation of lattice laser.
An example of the indirect sweep sequence with a final shaking frequency ff = 21 kHz and a final shaking amplitude \({{{\mathcal{A}}}}=1.9\)nm. a, b and c show variations of the modulation depth Al (the shaking amplitude \({{{\mathcal{A}}}}\)), the shaking frequency f and the laser frequency fl (the displacement of the lattice s), respectively.
Extended Data Fig. 4 Measured band-edge population after different sweep durations for different shaking amplitudes.
a and b show the final population \({{{{\mathcal{N}}}}}_{\pi }\) after direct sweeps in the forward (from a MI to a π-SF state) and backward (from a π-SF to a MI state) directions, respectively. We extract \(\partial {{{{\mathcal{N}}}}}_{\pi }/\partial \tau\) by the linear fits (solid lines). The fit results are shown in Fig. 4c,d.
Extended Data Fig. 5 The band-edge population \({{{{\mathcal{N}}}}}_{\pi }\).
(a) Atom numbers around k = 0 (n0) and k = ± k0 (nπ) are counted inside the boxes in blue and red, respectively. Note that nπ is the sum over the two red boxes. (b-f) are measured with different box sizes lbox/k0 = 0.1, 0.2, 0.4, 0.6, and 0.8, respectively.
Supplementary information
Supplementary Information
Supplementary Sections I–IV and Figs. 1–6.
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Song, B., Dutta, S., Bhave, S. et al. Realizing discontinuous quantum phase transitions in a strongly correlated driven optical lattice. Nat. Phys. 18, 259–264 (2022). https://doi.org/10.1038/s41567-021-01476-w
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DOI: https://doi.org/10.1038/s41567-021-01476-w
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