ICTS

In this talk I will report on the experimental realization of far-from-equilibrium dynamics of the Dicke model in a closed system of ~100 trapped ions arranged in a two-dimensional crystal. This highly controllable platform allows us to study how collective spins and vibrational motion interact across regimes ranging from simple and nearly integrable to strongly coupled and chaotic. We observe a dynamical phase transition, the onset of quantum chaos beyond mean-field descriptions, and the growth of quantum correlations associated with thermalization. We further infer quantum-fluctuation-driven spin squeezing below the standard quantum limit, followed by coherent collapses and revivals, demonstrating long-lived coherence in a strongly interacting many-body system.

I will talk about how one can use permutation symmetry and a local incoherent pump to generate W states of N distant qubits. The model consists of N identical spin-1/2 chains coupled to a central spin via an ancilla. Incoherently pumping the central qubit drives the system to an exactly solvable matrix product state of bond dimension 2, after which a global parity measurement projects the outermost qubits to a W state. For N=2 one gets a rainbow state. The protocol is based on fermonic quantum simulation with local operators on a star geometry. I will discuss how one may realize the required central coupling by Floquet engineering.

Ultracold polar molecules are an exciting platform for quantum science and technology. The combination of rich internal structure of vibration and rotation, controllable long-range dipolar interactions and strong coupling to applied electric and microwave fields has inspired many applications. These include quantum simulation of strongly interacting many-body systems, the study of quantum magnetism, quantum metrology and molecular clocks, quantum computation, precision tests of fundamental physics and the exploration of ultracold chemistry. Many of these applications require full quantum control of both the internal and motional degrees of freedom of the molecule at the single particle level, combined with traps that support long coherence times for rotational-state superpositions.

Using ultracold RbCs molecules assembled from ultracold atoms, we demonstrate all these requirements. We present a novel magic-wavelength trap that supports second-scale rotational coherences in a gas of molecules and gives access to controllable dipole-dipole interactions. We also report the efficient assembly of individual molecules in optical tweezers. By transferring the molecules into magic-wavelength tweezers, we demonstrate long-lived rotational coherences. In the magic-wavelength tweezers we can resolve Hertz-scale dipolar interactions between pairs of molecules. We then use the dipolar interaction to engineer entanglement, both using a spin-exchange protocol and by direct microwave excitation. Correcting for leakage errors, we measure an entanglement fidelity of 0.976 +/- 0.015.

Finally, as an outlook, we discuss progress towards a quantum gas microscope for ultracold molecules. We demonstrate in-situ detection of individual molecules in a thermal bulk gas by pinning in a deep 2D optical lattice prior to dissociation and detection. Further, by mapping two internal states of the molecule to different atomic species, we demonstrate simultaneous detection of the position and rotational state of individual molecules, paving the way to simulations of quantum magnetism with single-site and spin-resolved detection.

An important advance in quantum simulation of many-body systems with ultracold atoms has been the development of quantum gas microscopes, with single particle detection and manipulation. Applying these techniques to ultracold molecules allows for the study of a wider variety of models, including anisotropic Hamiltonians and many-body phases due to the molecules’ rich internal structure and the long-range dipolar interactions [1]. Here, we demonstrate spin-resolved detection of single ultracold molecules in an optical lattice [2].
Synthetic dimensions involve using an internal degree of freedom of the system to simulate an extra spatial dimension. We use a stroboscopic microwave scheme to couple multiple rotational states of the molecule and realise a synthetic dimension within the internal structure of the molecules. Using only the different rotational states of the molecule, we prepare a one-dimensional synthetic lattice, realising the SSH (Su–Schrieffer–Heeger) model for up to 8 synthetic lattice sites. We probe the bulk states and edge states of the system as well as the topological phase transition described by the model. We utilise the long lifetimes and coherence times afforded to us by molecules to accurately measure the edge state energy splitting and show the topological protection of the edge states in this model.

[1] Cornish, S.L., Tarbutt, M.R. and Hazzard, K.R.A., Nature Physics 20(5), 730 (2024).
[2] J. M. Mortlock, A. P. Raghuram, B. P. Maddox, P. D. Gregory, and S. L. Cornish. arXiv:2506.12329v1 (2025)
[3] Sundar, B., Gadway, B. & Hazzard, K.R.A. Sci Rep 8, 3422 (2018).

I shall talk about non-invasive detection of spin coherence in a collection of Raman driven cold atoms using dispersive Faraday rotation fluctuation measurements, which opens possibilities of probing spin correlations in quantum gases and other similar systems. We can measure various atomic, magnetic and sub-atomic properties as well as perform precision magnetometry (sensing) using Spin Noise Spectroscopy (SNS) in an atomic ensemble and show that it has better resolution than typical absorption spectroscopy in detecting spectral lines.

I shall show a minimally perturbative detection method, based on Raman Driven SNS (RDSNS) to directly probe the local density of a cloud of cold atoms in real time. Unlike traditional fluorescence and absorption imaging techniques, this approach does not require stochastic photon scattering from trapped atoms, thereby leaving the cold cloud unperturbed. The data can be collected in MHz refresh rate, allowing for near real-time detection. This detection protocol is particularly advantageous for probing systems that lack inherent symmetry and can have important application in the domain of neutral atom based quantum computing platforms.

Reference:

1. Sayari Majumder, Bhagyashri Bidwai, Bernadette Varsha, Saptarishi Chaudhuri, Appl. Phys. Lett. 127, 044004 (2025)
2. S. Majumder and S. Chaudhuri, IEEE Transactions on Instrumentation and Measurement, vol. 74, pp. 1-10, 2025

We consider a gas of non-interacting fermions that is released from a box into the vacuum and look at the entanglement between the escaped particles with those in the box. This provides a simple analytically tractable model that reproduces many features of the Page curve characterizing the evolution of entanglement entropy during evaporation of a black hole. Apart from the entropy we consider several other physical observables and show that the framework of generalized hydrodynamics provides a rather surprisingly accurate description of the quantum dynamics. We also report numerical results for interacting fermions.

We study a chain of periodically driven Rydberg atoms and identify a class of drive protocols for which the driven chain exhibits emergent prethermal Bethe integrability at special drive frequencies. We provide a perturbative, analytic, expression of its Floquet Hamiltonian in the large drive amplitude regime. We demonstrate integrability of the leading term of this Floquet Hamiltonian at special drive frequencies, which we identify, by mapping it to the Hamiltonian of a XXZ spin chain. We support our analytical results by exact diagonalization studies on finite chain; our numerical results on level statistics, average magnetization, and spin-spin autocorrelation function of the driven chain brings out its integrable nature at these frequencies up to a large prethermal timescale. We discuss experiments that can test our theory.

Going beyond short-range interactions, we explore the role of long-range interactions in the extended XY model for transferring quantum states through evolution. In particular, employing a spin-1/2 chain with interactions decaying as a power law, we demonstrate that long-range (LR) interactions significantly enhance the efficiency of a quantum state transfer (QST) protocol, improving the achievable fidelity, mitigating its slow decline as compared with the nearest-neighbor setting, associated with increasing system-size. Our study identifies the LR regime as providing an optimal balance between interaction range and transfer efficiency, outperforming the protocol with the short-range interacting model. Our detailed analysis reveals the impact of system parameters, such as anisotropy, magnetic field strength, and coordination number, on QST dynamics. Specifically, we find that intermediate coordination numbers lead to a faster and more reliable state transfer, while extreme values diminish performance. Furthermore, we exhibit that the presence of LR interactions considerably reduces the minimum time required to achieve fidelity beyond the classical limit. In addition, we analyze the impact of non-Hermiticity in the quantum state transmission by employing a non-Hermitian spin chain that functions as a quantum data bus.

Polarization forces are ubiquitous in nature, spanning both animate and inanimate systems. They are most commonly described in terms of pairwise interactions. In this talk, we explore two settings in which this binary description breaks down, revealing the importance of genuine few-body effects.

In the first part, we revisit the validity of the pairwise approximation in lattice systems of Rydberg atoms. We identify regimes where the binary picture holds, as well as conditions under which additional interaction terms become essential. In particular, we highlight special regimes near a Förster resonance where three-body interactions are strongly enhanced. We discuss ongoing efforts to derive effective low-energy Hamiltonians and to characterize the resulting many-body quantum behavior in and around these regimes.

In the second part, we turn to Rydberg macrodimers, diatomic molecules with micron-scale bond lengths. These systems exhibit remarkable single-molecule properties, including a spectrum of shallow vibrational states that have recently been probed using quantum gas microscopy. We compute the intermolecular interactions between macrodimers, which arise from the Rydberg character of their constituent atoms, and map out the resulting anisotropic molecular potentials. Based on this, we predict a molecular excitation blockade and present comparisons with experimental data that provide first evidence of this effect.

Quantum droplets (QDs) have recently emerged as a novel state of matter in ultracold atomic systems, where self-bound states arise from the interplay between mean-field (MF) interactions and beyond-mean-field (BMF) quantum fluctuations. While in higher dimensions droplets typically form due to attractive MF and repulsive BMF contributions, in one-dimensional binary systems the mechanism is reversed, with repulsive MF balanced by attractive BMF interactions. In the first half of this talk, we focus on the structure and dynamics of quantum droplets in one-dimensional spin–orbit coupled binary Bose–Einstein condensates, presenting numerical results on how both vanishingly small and finite MF interactions affect droplet stability, shape, and evolution. We also discuss dynamical responses induced by velocity perturbations, quenches in spin–orbit or Rabi coupling, and control of droplet properties via population imbalance between pseudo-spin components. In the second part of the talk, we turn to turbulent dynamics in two-dimensional condensates, where turbulence is generated using a rotating external paddling potential. By tuning the rotation strength and angular velocity, we identify different turbulent regimes, including vortex dipoles, vortex clusters, and randomly distributed vortex–antivortex pairs, and analyze their corresponding energy spectra, revealing Kolmogorov- and Vinen-type scaling behaviors in different configurations.

Efficient light-matter interfaces are a cornerstone for scalable quantum technologies, with nanophotonic platforms offering unprecedented control over light-matter interactions. In this work, we propose and analyze a composite waveguide system consisting of two parallel optical nanofibers to significantly enhance photon-emitter interactions. Using a full 3D Green’s tensor formalism, we develop a rigorous and computationally efficient framework to capture the full radiation dynamics, including both guided and radiation modes.

We show that the composite geometry leads to a substantial enhancement in photon coupling efficiency compared to single nanofiber systems, resulting in stronger and more robust long-range entanglement between emitters [1]. Furthermore, the system enables tunable, position-dependent chiral emission, providing precise control over photon directionality for efficient quantum state routing. We also observe superradiant and subradiant collective states in arrays of emitters, where long-lived subradiant modes can be exploited for quantum memory applications. These results establish composite nanofiber platforms as a promising route toward scalable fiber-based quantum technologies.

References:

[1] K. Jain, L. Ruks, F. Le Kien, and T. Busch, “Strong dipole-dipole interactions via enhanced light-matter coupling in composite nanofiber waveguides,” Phys. Rev. Research 6, 033311 (2024).

Supersolids, quantum phases that simultaneously exhibit crystalline order and superfluidity, provide a unique platform to explore the interplay of broken continuous symmetries and collective excitations. In this presentation, we will discuss the excitation spectrum of dipolar quantum gases across the superfluid-to-supersolid phase transition, with particular emphasis on the emergence and detection of amplitude (Higgs) modes.
Higgs-like amplitude modes are notoriously difficult to observe in condensed matter systems, including supersolids in harmonic potentials. To mitigate this mode coupling, we consider toroidal trapping potentials, whose continuous rotational symmetry and periodic boundary conditions along the azimuthal direction establish a direct connection between experimentally accessible finite-size systems and bulk supersolids described within mean-field theory. Within this framework, we compute the elementary excitation spectrum across the phase transition and demonstrate the emergence of first sound, second sound, and Higgs amplitude modes in dipolar supersolids.
Furthermore, we propose an interferometric protocol to probe Higgs amplitude excitations by exploiting the temporal Talbot effect in a toroidal geometry. This approach enables the creation and real-space detection of localized Higgs wave packets. The resulting “quantum carpet” dynamics reveal the quadratic dispersion of amplitude modes and allow for a direct extraction of the effective mass of the Higgs quasiparticle from revival times.

Critical points in disordered quantums system are very special points in the parameter space where localization transitions happen. Moreover, near-critical points have been proposed for enhanced quantum sensing. However, these critical points are very fine-tuned and fragile under external perturbations. For example, the paradigmatic Aubry-Andre-Harper (AAH) model in one dimension where all the single-particle eigenstates undergo the delocalization-localization transition at the critical strength of the quasiperiodic potential, protected by self-duality. Hence, two relevant questions are in order: can the self-duality (criticality) re-emerge in the AAH model even with duality-breaking perturbation? Can we obtain a broadened critical phase, instead of a point, in a quasiperiodic chain in presence of interactions? I will briefly talk about our recent works addressing these two questions.