arXiv subjects

Giacomo Valtolina

Publications and source records attributed to Giacomo Valtolina.

12 recordsLinked to original sources

arXiv2026

Temperature-induced effective topology in many-body ultracold atomic quantum systems

Ultracold atomic quantum systems offer an unprecedentedly powerful platform for exploring interacting symmetry-protected topological phases. Here, we show that their characteristic control over temperature provides a resource for engineering effective topological regimes with no zero-temperature counterpart. Employing finite-temperature matrix-product-state calculations, we investigate experimentally accessible Hamiltonians - the interacting bosonic Su-Schrieffer-Heeger and spin-1 XXZ chains - that host a topological phase at zero temperature, as well as a fermionic dipolar ladder model whose ground state exhibits no topological order. By tracking complementary topological markers, we identify an intriguing mechanism rooted in the structure of the zero-temperature phase diagrams: in finite-size systems, excitation gaps with different magnitudes define an intermediate-temperature window where the correlations associated with the lower gap are suppressed, while those protected by the larger gap persist. This enables the emergence of effective finite-temperature regimes exhibiting topological features that are either absent or qualitatively different from those at zero temperature. Our results establish a novel route toward exploring effective topological phases in ultracold atomic quantum systems.

cond-mat.quant-gas↗

arXiv2026

Magnetic atoms with a large electric dipole moment

We experimentally show that an electric dipole moment of more than 1 Debye can be induced in the dysprosium (Dy) atom, in a long-lived state that is about 17513 cm$^{-1}$ above the ground state. This metastable state is part of a strongly coupled opposite-parity doublet. Using optically detected microwave spectroscopy in an atomic beam, we determine the approximately 1.12 cm$^{-1}$ doublet spacing for the five stable bosonic isotopes of Dy with kHz-level accuracy. From the shift of the microwave transition frequency in low electric fields (below 150 V/cm) and from optical spectra in high electric fields (up to 150 kV/cm), a reduced transition dipole moment of 7.65 $\pm$ 0.05 Debye between the doublet states is extracted. In high electric fields the doublet interacts with a third state at 17727 cm$^{-1}$, that connects to the ground state via an electric-dipole transition. The three-state Stark interaction enables preparation of Dy atoms in the metastable state via single-photon excitation from the ground state.

physics.atom-ph↗

arXiv2025

Accelerated Hydrogen Exchange Reaction in a Dark Cavity: A Benchmark for Bridging the Gap Between Theory and Experiment

The gas-phase hydrogen exchange reaction (HER) is the most fundamental chemical process for benchmarking quantum reaction dynamics. In this Letter, we focus on controlling HER by means of strong light-matter coupling inside a resonant cavity, an approach often called polariton chemistry. In particular, we focus on the isotopic variation of HER involving collisions between molecular hydrogen H$_2$ and deuterium atom D, i.e., H$_2$+D$\to$HD+H. We find that the asymmetry introduced by the different isotopes, despite being small, enables strong cavity-induced modifications of reaction rates. Outside of the cavity the reaction is as usual D+H${_2}$$\to$DH+H. However, inside the cavity another type of reactions take place where D+H$_2$$\to$DH+H+E$_{photon}$, where E$_{photon}$=$\hbarω_{cav}$. Our results show that HER is an ideal platform to make a significant step toward closing the gap between theory and experiment in polariton chemistry.

physics.chem-ph↗

arXiv2024

Cold molecular ions via autoionization below the dissociation limit

Several diatomic transition metal oxides, rare-earth metal oxides and fluorides have the unusual property that their bond dissociation energy is larger than their ionization energy. In these molecules, bound levels above the ionization energy can be populated via strong, resonant transitions from the ground state. The only relevant decay channel of these levels is autoionization; predissociation is energetically not possible and radiative decay is many orders of magnitude slower. Starting from translationally cold neutral molecules, translationally cold molecular ions can thus be produced with very high efficiency. By populating bound levels just above the ionization energy, internally cold molecular ions, exclusively occupying the lowest rotational level, are produced. This is experimentally shown here for the dysprosium monoxide molecule, DyO, for which the lowest bond dissociation energy is determined to be 0.0831(6) eV above the ionization energy.

physics.atm-clus↗

arXiv2024

Quantum state manipulation and cooling of ultracold molecules

An increasingly large variety of molecular species are being cooled down to low energies in recent years, and innovative ideas and powerful techniques continue to emerge to gain ever more precise control of molecular motion. In this brief review we focus our discussions on two widely employed cooling techniques that have brought molecular gases into the quantum regime: association of ultracold atomic gases into quantum gases of molecules and direct laser cooling of molecules. These advances have brought into reality our capability to prepare and manipulate both internal and external states of molecules quantum mechanically, opening the field of cold molecules to a wide range of scientific explorations.

cond-mat.quant-gas↗

arXiv2022

Dynamical generation of spin squeezing in ultra-cold dipolar molecules

We study a bulk fermionic dipolar molecular gas in the quantum degenerate regime confined in a two-dimensional geometry. We consider two rotational states that encode a spin 1/2 degree of freedom. We derive a long-range interacting XXZ model describing the many-body spin dynamics of the molecules valid in the regime where motional degrees of freedom are frozen. Due to the spatially extended nature of the harmonic oscillator modes, the interactions in the spin model are very long-ranged and the system behaves close to the collective limit, resulting in robust dynamics and generation of entanglement in the form of spin squeezing even at finite temperature and in presence of dephasing and chemical reactions. We demonstrate how the internal state structure can be exploited to realise time-reversal and enhanced metrological sensing protocols.

quant-ph↗

arXiv2021

Tuning of dipolar interactions and evaporative cooling in a three-dimensional molecular quantum gas

Ultracold polar molecules possess long-range, anisotropic, and tunable dipolar interactions, providing the opportunities to probe quantum phenomena inaccessible with existing cold gas platforms. However, experimental progress has been hindered by the dominance of two-body loss over elastic interactions, which prevents efficient evaporative cooling. Though recent work has demonstrated controlled interactions by confining molecules to a two-dimensional geometry, a general approach for tuning molecular interactions in a three-dimensional (3D), stable system has been lacking. Here, we demonstrate tunable elastic dipolar interactions in a bulk gas of ultracold 40K87Rb molecules in 3D, facilitated by an electric field-induced shielding resonance which suppresses the reactive loss by a factor of thirty. This improvement in the ratio of elastic to inelastic collisions enables direct thermalization. The thermalization rate depends on the angle between the collisional axis and the dipole orientation controlled by an external electric field, a direct manifestation of the anisotropic dipolar interaction. We achieve evaporative cooling mediated by the dipolar interactions in three dimensions. This work demonstrates full control of a long-lived bulk quantum gas system with tunable long-range interactions, paving the way for the study of collective quantum many-body physics.

cond-mat.quant-gas↗

arXiv2020

Resonant collisional shielding of reactive molecules using electric fields

Full control of molecular interactions, including reactive losses, would open new frontiers in quantum science. Here, we demonstrate extreme tunability of chemical reaction rates by using an external electric field to shift excited collision channels of ultracold molecules into degeneracy with the initial collision channel. In this situation, resonant dipolar interactions mix the channels at long range, dramatically altering the intermolecular potential. We prepare fermionic potassium-rubidium (KRb) molecules in their first excited rotational state and observe a three orders-of-magnitude modulation of the chemical reaction rate as we tune the electric field strength by a few percent across resonance. In a quasi-two-dimensional geometry, we accurately determine the contributions from the three lowest angular momentum projections of the collisions. Using the resonant features, we shield the molecules from loss and suppress the reaction rate by up to an order of magnitude below the background value, realizing a long-lived sample of polar molecules in large electric fields.

cond-mat.quant-gas↗

arXiv2020

Dipolar evaporation of reactive molecules to below the Fermi temperature

Molecules are the building blocks of matter and their control is key to the investigation of new quantum phases, where rich degrees of freedom can be used to encode information and strong interactions can be precisely tuned. Inelastic losses in molecular collisions, however, have greatly hampered the engineering of low-entropy molecular systems. So far, the only quantum degenerate gas of molecules has been created via association of two highly degenerate atomic gases. Here, we use an external electric field along with optical lattice confinement to create a two-dimensional (2D) Fermi gas of spin-polarized potassium-rubidium (KRb) polar molecules, where elastic, tunable dipolar interactions dominate over all inelastic processes. Direct thermalization among the molecules in the trap leads to efficient dipolar evaporative cooling, yielding a rapid increase in phase-space density. At the onset of quantum degeneracy, we observe the effects of Fermi statistics on the thermodynamics of the molecular gas. These results demonstrate a general strategy for achieving quantum degeneracy in dipolar molecular gases to explore strongly interacting many-body phases.

cond-mat.quant-gas↗

arXiv2020

Quantum Many-Body Physics with Ultracold Polar Molecules: Nanostructured Potential Barriers and Interactions

We design dipolar quantum many-body Hamiltonians that will facilitate the realization of exotic quantum phases under current experimental conditions achieved for polar molecules. The main idea is to modulate both single-body potential barriers and two-body dipolar interactions on a spatial scale of tens of nanometers to strongly enhance energy scales and, therefore, relax temperature requirements for observing new quantum phases of engineered many-body systems. We consider and compare two approaches. In the first, nanoscale barriers are generated with standing wave optical light fields exploiting optical nonlinearities. In the second, static electric field gradients in combination with microwave dressing are used to write nanostructured spatial patterns on the induced electric dipole moments, and thus dipolar interactions. We study the formation of inter-layer and interface bound states of molecules in these configurations, and provide detailed estimates for binding energies and expected losses for present experimental setups.

cond-mat.quant-gas↗

arXiv2019

Thermalization and Sub-Poissonian Density Fluctuations in a Degenerate Molecular Fermi Gas

We observe thermalization in the production of a degenerate Fermi gas of polar ${}^{40}\text{K}{}^{87}\text{Rb}$ molecules. By measuring the atom--dimer elastic scattering cross section near the Feshbach resonance, we show that Feshbach molecules rapidly reach thermal equilibrium with both parent atomic species. Equilibrium is essentially maintained through coherent transfer to the ground state. Sub-Poissonian density fluctuations in Feshbach and ground-state molecules are measured, giving an independent characterization of degeneracy and directly probing the molecular Fermi--Dirac distribution.

cond-mat.quant-gas↗

arXiv2018

A Fermi Degenerate Gas of Polar Molecules

It has long been expected that quantum degenerate gases of molecules would open access to a wide range of phenomena in molecular and quantum sciences. However, the very complexity that makes ultracold molecules so enticing has made reaching degeneracy an outstanding experimental challenge over the past decade. We now report the production of a Fermi degenerate gas of ultracold polar molecules of potassium--rubidium (KRb). Through coherent adiabatic association in a deeply degenerate mixture of a rubidium Bose-Einstein condensate and a potassium Fermi gas, we produce molecules at temperatures below 0.3 times the Fermi temperature. We explore the properties of this reactive gas and demonstrate how degeneracy suppresses chemical reactions, making a long-lived degenerate gas of polar molecules a reality.

physics.atom-ph↗