Publications

Order by: publication date number of citations

• Feedback cooling of fermionic atoms in optical lattices

  Wenhua Zhao, Ling-Na Wu, Francesco Petiziol, André Eckardt

  SciPost Phys. 19, 073 (2025) · published 25 September 2025 | Toggle abstract · pdf

  We discuss the preparation of topological insulator states with fermionic ultracold atoms in optical lattices by means of measurement-based Markovian feedback control. The designed measurement and feedback operators induce an effective dissipative channel that stabilizes the desired insulator state, either in an exact way or approximately in the case where additional experimental constraints are assumed. Successful state preparation is demonstrated in one-dimensional insulators as well as for Haldane's Chern insulator, by calculating the fidelity between the target ground state and the steady state of the feedback-modified master equation. The fidelity is obtained numerically through exact diagonalization or via time evolution of the system with moderate sizes. For larger 2D systems, we compare the mean occupation of the single-particle eigenstates for the ground and steady state computed through mean-field kinetic equations.

• Dipolar magnetostirring protocol for three-well atomtronic circuits

  Héctor Briongos-Merino, Felipe Isaule, Montserrat Guilleumas, Bruno Juliá-Díaz

  SciPost Phys. 19, 059 (2025) · published 27 August 2025 | Toggle abstract · pdf

  We propose a magnetostirring protocol to create persistent currents on an annular system. Under this protocol, polar bosons confined in a three-well ring circuit reach a state with high average circulation. We model the system with an extended Bose-Hubbard Hamiltonian and show that the protocol can create circulation in an atomtronic circuit for a range of tunable parameters. The performance and robustness of this scheme are examined, in particular considering different interaction regimes. We also present a method for predicting the optimal protocol parameters, which improves protocol's scalability and enables its application to systems with large numbers of bosons. This overcomes computational limitations and paves the way for exploring macroscopic quantum phenomena.

• Many-body open quantum systems

  Rosario Fazio, Jonathan Keeling, Leonardo Mazza, Marco Schirò

  SciPost Phys. Lect. Notes 99 (2025) · published 14 August 2025 | Toggle abstract · pdf

  These lecture notes discuss the recent theoretical advances in the understanding of open quantum many-body physics in platforms where both dissipative and coherent processes can be tuned and controlled to a high degree. We start by reviewing the theoretical frameworks and methods used to describe and tackle open quantum many-body systems. We then discuss the use of dissipative processes to engineer many-body stationary states with desired properties and the emergence of dissipative phase transitions arising out of the competition between coherent evolution and dissipation. We review the dynamics of open quantum many body systems in the presence of correlated many-body dissipative processes, such as heating and many-body losses. Finally we provide a different perspective on open quantum many-body systems by looking at stochastic quantum trajectories, relevant for the case in which the environment represents a monitoring device, and the associated measurement-induced phase transitions.

  13 citations

• Z2 topological orders in kagome dipolar systems: Feedback from Rydberg quantum simulator

  Pengwei Zhao, Gang v. Chen

  SciPost Phys. 19, 040 (2025) · published 14 August 2025 | Toggle abstract · pdf

  The mutual feedback between quantum condensed matter and cold atom physics has been quite fruitful throughout history and continues to inspire ongoing research. Motivated by the recent activities on the quantum simulation of topological orders among the ultracold Rydberg atom arrays, we consider the possibility of searching for topological orders among the dipolar quantum magnets and polar molecules with a kagome lattice geometry. Together with other quantum interactions such as the transverse field, the dipolar interaction endows the kagome system with a similar structure as the Balents-Fisher-Girvin model and thus fosters the emergence of the $\mathbb{Z}_2$ topological orders. We construct a $\mathbb{Z}_2$ lattice gauge theory to access the topological ordered phase and describe the spinon and vison excitations for the $\mathbb{Z}_2$ topological orders. We explain the spectroscopic consequences for various quantum phases as well as the experimental detection. We further discuss the rare-earth kagome magnets, ultracold polar molecules, and cluster Mott insulators for the physical realization.

• Mechanical stability of resonant Bose-Fermi mixtures

  Christian Gualerzi, Leonardo Pisani, Pierbiagio Pieri

  SciPost Phys. 19, 039 (2025) · published 14 August 2025 | Toggle abstract · pdf

  We investigate the mechanical stability of Bose-Fermi mixtures at zero temperature in the presence of a tunable Feshbach resonance, which induces a competition between boson condensation and boson-fermion pairing when the boson density is smaller than the fermion density. Using a many-body diagrammatic approach validated by fixed-node Quantum Monte Carlo calculations and supported by recent experimental observations, we determine the minimal amount of boson-boson repulsion required to guarantee the stability of the mixture across the entire range of boson-fermion interactions from weak to strong coupling. Our stability phase diagrams indicate that mixtures with boson-to-fermion mass ratios near two, such as the $^{87}$Rb-$^{40}$K system, exhibit optimal stability conditions. Moreover, by applying our results to a recent experiment with a $^{23}$Na-$^{40}$K mixture, we find that the boson-boson repulsion was insufficient to ensure stability, suggesting that the experimental timescale was short enough to avoid mechanical collapse. On the other hand, we also show that even in the absence of boson-boson repulsion, Bose-Fermi mixtures become intrinsically stable beyond a certain coupling strength, preceding the quantum phase transition associated with the vanishing of the bosonic condensate. We thus propose an experimental protocol for observing this quantum phase transition in a mechanically stable configuration.

• Beyond-mean-field analysis of the Townes soliton and its breathing mode

  Dmitry S. Petrov

  SciPost Phys. 19, 037 (2025) · published 13 August 2025 | Toggle abstract · pdf

  By using the Bogoliubov perturbation theory we describe the self-bound ground state and excited breathing states of $N$ two-dimensional bosons with zero-range attractive interactions. Our results for the ground state energy $B_N$ and size $R_N$ improve previously known large-$N$ asymptotes and we better understand the crossover to the few-body regime. The breathing oscillations, absent at the mean-field level, result from the quantum-mechanical breaking of the mean-field scale symmetry. The breathing-mode frequency scales as $\Omega\propto |B_N|/\sqrt{N}$ at large $N$.

• Efficiency of dynamical decoupling for (almost) any spin–boson model

  Alexander Hahn, Daniel Burgarth, Davide Lonigro

  SciPost Phys. 19, 035 (2025) · published 13 August 2025 | Toggle abstract · pdf

  Dynamical decoupling is a technique aimed at suppressing the interaction between a quantum system and its environment by applying frequent unitary operations on the system alone. In the present paper, we analytically study the dynamical decoupling of a two-level system coupled with a structured bosonic environment initially prepared in a thermal state. We find sufficient conditions under which dynamical decoupling works for such systems, and—most importantly—we find bounds for the convergence speed of the procedure. Our analysis is based on a new Trotter theorem for multiple Hamiltonians and involves a rigorous treatment of the evolution of mixed quantum states via unbounded Hamiltonians. A comparison with numerical experiments shows that our bounds reproduce the correct scaling in various relevant system parameters. Furthermore, our analytical treatment allows for quantifying the decoupling efficiency for boson baths with infinitely many modes, in which case a numerical treatment is unavailable.

  1 citation

• Velocity gauge formulation of nonlinear optical response in Floquet quantum systems

  S. Sajad Dabiri, Reza Asgari

  SciPost Phys. Core 8, 049 (2025) · published 21 July 2025 | Toggle abstract · pdf

  Using the velocity gauge formalism, we develop a theoretical framework for computing the nonlinear optical responses of time-periodic quantum systems. This approach complements the length gauge formulation and offers distinct advantages in both numerical and analytical treatments, particularly for atomic and solid-state systems with well-defined momentum-space structures. By applying our framework to the Rabi model, we derive numerical solutions in the velocity gauge and compare them with the length gauge, demonstrating full agreement between the two formulations. Our findings reveal rich optical phenomena, including photon-assisted transitions, frequency mixing effects, and emergent Floquet-induced photocurrents that are absent in static systems. We demonstrate that nonlinear responses in Floquet-driven systems exhibit resonances at integer multiples of the driving frequency, providing insights into ultrafast spectroscopy and Floquet engineering of quantum materials. The present formulation establishes a bridge between theoretical models and experimental observations in driven quantum systems, with potential applications in quantum optics, photonics, and next-generation optoelectronic devices.

• Tunable anharmonicity in cavity optomechanics in the unresolved sideband regime

  Jonathan L. Wise, Clement Dutreix, Fabio Pistolesi

  SciPost Phys. 19, 016 (2025) · published 16 July 2025 | Toggle abstract · pdf

  Introducing a controlled and strong anharmonicity in mechanical systems is a present challenge of nanomechanics. In cavity optomechanics a mechanical oscillator may be made anharmonic by ponderomotively coupling its motion to the light field of a laser-driven cavity. In the regime where the mechanical resonating frequency and the single-photon coupling constant are small compared to the decay rate of the cavity field, it turns out that the quantum electromagnetic fluctuations of the laser field drive the oscillator into a high-temperature thermal state. The motional state may however be highly non-Gaussian; we show that a precise tuning of system parameters may even lead to a purely quartic effective potential for the mechanical oscillator. We present a theory that predicts the measurable signatures left by the mechanical anharmonicity. In particular, we obtain analytically and numerically the mechanical displacement spectrum, and explore the imprints of the mechanical anharmonicity on the cavity light field.

• Acceleration-induced transport of quantum vortices in joined atomtronic circuits

  Andrii Chaika, Artem O. Oliinyk, Ihor V. Yatsuta, Nick P. Proukakis, Mark Edwards, Alexander I. Yakimenko, Thomas Bland

  SciPost Phys. 19, 005 (2025) · published 2 July 2025 | Toggle abstract · pdf

  Persistent currents–inviscid quantized flow around an atomic circuit–are a crucial building block of atomtronic devices. We investigate how acceleration influences the transfer of persistent currents between two density-connected, ring-shaped atomic Bose-Einstein condensates, joined by a tunable weak link that controls system topology. We find that the acceleration of this system modifies both the density and phase dynamics between the rings, leading to a bias in the periodic vortex oscillations studied in T. Bland et al., Phys. Rev. Research 4, 043171 (2022). Accounting for dissipation suppressing such vortex oscillations, the acceleration facilitates a unilateral vortex transfer to the leading ring. We analyze how this transfer depends on the weak-link amplitude, the initial persistent current configuration, and the acceleration strength and direction. Characterization of the sensitivity to these parameters paves the way for a new platform for acceleration measurements, for which we outline a proof-of-concept ultracold double-ring accelerometer.

  1 citation