arXiv subjects

G. Pupillo

Publications and source records attributed to G. Pupillo.

At least 37 records · Page 2Linked to original sources

arXiv2015

Conductivity in organic semiconductors hybridized with the vacuum field

Organic semiconductors have generated considerable interest for their potential for creating inexpensive and flexible devices easily processed on a large scale [1-11]. However technological applications are currently limited by the low mobility of the charge carriers associated with the disorder in these materials [5-8]. Much effort over the past decades has therefore been focused on optimizing the organisation of the material or the devices to improve carrier mobility. Here we take a radically different path to solving this problem, namely by injecting carriers into states that are hybridized to the vacuum electromagnetic field. These are coherent states that can extend over as many as 10^5 molecules and should thereby favour conductivity in such materials. To test this idea, organic semiconductors were strongly coupled to the vacuum electromagnetic field on plasmonic structures to form polaritonic states with large Rabi splittings ca. 0.7 eV. Conductivity experiments show that indeed the current does increase by an order of magnitude at resonance in the coupled state, reflecting mostly a change in field-effect mobility as revealed when the structure is gated in a transistor configuration. A theoretical quantum model is presented that confirms the delocalization of the wave-functions of the hybridized states and the consequences on the conductivity. While this is a proof-of-principle study, in practice conductivity mediated by light-matter hybridized states is easy to implement and we therefore expect that it will be used to improve organic devices. More broadly our findings illustrate the potential of engineering the vacuum electromagnetic environment to modify and to improve properties of materials.

cond-mat.mtrl-sci↗

arXiv2015

Cluster Luttinger liquids and emergent supersymmetric conformal critical points in the one-dimensional soft-shoulder Hubbard model

We investigate the quantum phases of hard-core bosonic atoms in an extended Hubbard model where particles interact via soft-shoulder potentials in one dimension. Using a combination of field-theoretical methods and strong-coupling perturbation theory, we demonstrate that the low-energy phase can be a conformal cluster Luttinger liquid (CLL) phase with central charge $c=1$, where the microscopic degrees of freedom correspond to mesoscopic ensembles of particles. Using numerical density-matrix-renormalization-group methods, we demonstrate that the CLL phase, first predicted in [Phys. Rev. Lett. 111, 165302 (2013)], is separated from a conventional Tomonaga-Luttinger liquid by an exotic critical point with central charge $c=3/2$. The latter is expression of an emergent conformal supersymmetry, which is not present in the original Hamiltonian. We discuss the observability of the CLL phase in realistic experimental settings with weakly-dressed Rydberg atoms confined to optical lattices. Using quantum Monte-Carlo simulations, we show that the typical features of CLLs are stable up to comparatively high temperatures. Using exact diagonalizations and quantum trajectory methods, we provide a protocol for adiabatic state preparation as well as quantitative estimates on the effects of particle losses.

cond-mat.quant-gas↗

arXiv2013

Simulations of micrometeoroid interactions with the Earth atmosphere

Micrometeoroids (cosmic dust with size between a few $μ$m and $\sim$1 mm) dominate the annual extraterrestrial mass flux to the Earth. We investigate the range of physical processes occurring when micrometeoroids traverse the atmosphere. We compute the time (and altitude) dependent mass loss, energy balance, and dynamics to identify which processes determine their survival for a range of entry conditions. We develop a general numerical model for the micrometeoroid-atmosphere interaction. The equations of motion, energy, and mass balance are simultaneously solved for different entry conditions (e.g. initial radii, incident speeds and angles). Several different physical processes are taken into account in the equation of energy and in the mass balance, in order to understand their relative roles and evolution during the micrometeoroid-atmosphere interaction. In particular, to analyze the micrometeoroid thermal history we include in the energy balance: collisions with atmospheric particles, micrometeoroid radiation emission, evaporation, melting, sputtering and kinetic energy of the ablated mass. Low entry velocities and grazing incidence angles favor micrometeoroid survival. Among those that survive, our model distinguishes (1) micrometeoroids who reach the melting temperature and for which melting is the most effective mass loss mechanism, and (2) micrometeoroids for which ablation due to evaporation causes most of the the mass loss. Melting is the most effective cooling mechanism. Sputtering-induced mass loss is negligible.

astro-ph.EP↗

arXiv2012

Driven-dissipative dynamics of a strongly interacting Rydberg gas

We study the non-equilibrium many-body dynamics of a cold gas of ground state alkali atoms weakly admixed by Rydberg states with laser light. On a timescale shorter than the lifetime of the dressed states, effective dipole-dipole or van der Waals interactions between atoms can lead to the formation of strongly correlated phases, such as atomic crystals. Using a semiclassical approach, we study the long-time dynamics where decoherence and dissipative processes due to spontaneous emission and blackbody radiation dominate, leading to heating and melting of atomic crystals as well as particle losses. These effects can be substantially mitigated by performing active laser cooling in the presence of atomic dressing.

physics.atom-ph↗

arXiv2012

Condensed Matter Theory of Dipolar Quantum Gases

Recent experimental breakthroughs in trapping, cooling and controlling ultracold gases of polar molecules, magnetic and Rydberg atoms have paved the way toward the investigation of highly tunable quantum systems, where anisotropic, long-range dipolar interactions play a prominent role at the many-body level. In this article we review recent theoretical studies concerning the physics of such systems. Starting from a general discussion on interaction design techniques and microscopic Hamiltonians, we provide a summary of recent work focused on many-body properties of dipolar systems, including: weakly interacting Bose gases, weakly interacting Fermi gases, multilayer systems, strongly interacting dipolar gases and dipolar gases in 1D and quasi-1D geometries. Within each of these topics, purely dipolar effects and connections with experimental realizations are emphasized.

cond-mat.quant-gas↗

arXiv2012

Supersolid Vortex Crystals in Rydberg-dressed Bose-Einstein Condensates

We study rotating quasi-two-dimensional Bose-Einstein-condensates, in which atoms are dressed to a highly excited Rydberg state. This leads to weak effective interactions that induce a transition to a mesoscopic supersolid state. Considering slow rotation, we determine its superfluidity using Quantum Monte-Carlo simulations as well as mean field calculations. For rapid rotation, the latter reveal an interesting competition between the supersolid crystal structure and the rotation-induced vortex lattice that gives rise to new phases, including arrays of mesoscopic vortex crystals.

physics.atom-ph↗

arXiv2012

Engineered Open Systems and Quantum Simulations with Atoms and Ions

The enormous experimental progress in atomic, molecular and optical (AMO) physics during the last decades allows us nowadays to isolate single, a few or even many-body ensembles of microscopic particles, and to manipulate their quantum properties at a level of precision, which still seemed unthinkable some years ago. This versatile set of tools has enabled the development of the well-established concept of engineering of many-body Hamiltonians in various physical platforms. These available tools, however, can also be harnessed to extend the scenario of Hamiltonian engineering to a more general Liouvillian setting, which in addition to coherent dynamics also includes controlled dissipation in many-body quantum systems. Here, we review recent theoretical and experimental progress in different directions along these lines, with a particular focus on physical realizations with systems of atoms and ions. This comprises digital quantum simulations in a general open system setting, as well as engineering and understanding new classes of systems far away from thermodynamic equilibrium.

quant-ph↗

arXiv2011

Trimer liquids and crystals of polar molecules in coupled wires

We investigate the pairing and crystalline instabilities of bosonic and fermionic polar molecules confined to a ladder geometry. By means of analytical and quasi-exact numerical techniques, we show that gases of composite molecular dimers as well as trimers can be stabilized as a function of the density difference between the wires. A shallow optical lattice can pin both liquids, realizing crystals of composite bosons or fermions. We show that these exotic quantum phases should be realizable under current experimental conditions in finite-size confining potentials.

cond-mat.quant-gas↗

arXiv2010

1D Quantum Liquids with Power-Law Interactions: a Luttinger Staircase with Polar Molecules

We study one dimensional fermionic and bosonic gases with repulsive power-law interactions $1/|x|^β$, with $β>1$, in the framework of Tomonaga-Luttinger liquid (LL) theory. We obtain an accurate analytical expression linking the LL parameter to the microscopic Hamiltonian, for arbitrary $β$ and strength of the interactions. In the presence of a small periodic potential, power-law interactions make the LL unstable towards the formation of a cascade of lattice solids with fractional filling, thus forming a "Luttinger staircase". Several of these quantum phases and phase transitions are realized with groundstate polar molecules and weakly-bound magnetic Feshbach molecules.

cond-mat.quant-gas↗

arXiv2010

A superfluid-droplet crystal and a free-space supersolid in a dipole-blockaded gas

A novel supersolid phase is predicted for an ensemble of Rydberg atoms in the dipole-blockade regime, interacting via a repulsive dipolar potential "softened" at short distances. Using exact numerical techniques, we study the low temperature phase diagram of this system, and observe an intriguing phase consisting of a crystal of mesoscopic superfluid droplets. At low temperature, phase coherence throughout the whole system, and the ensuing bulk superfluidity, are established through tunnelling of identical particles between neighbouring droplets.

cond-mat.quant-gas↗

arXiv2010

Quantum Phases of Cold Polar Molecules in 2D Optical Lattices

We discuss the quantum phases of hard-core bosons on a two-dimensional square lattice interacting via repulsive dipole-dipole interactions, as realizable with polar molecules trapped in optical lattices. In the limit of small tunneling, we find evidence for a devil's staircase, where solid phases appear at all rational fillings of the underlying lattice. For finite tunneling, we establish the existence of extended regions of parameters where the groundstate is a supersolid, obtained by doping the solids either with particles or vacancies. Here the solid-superfluid quantum melting transition consists of two consecutive second-order transitions, with a supersolid as the intermediate phase. The effects of finite temperature and confining potentials relevant to experiments are discussed.

cond-mat.stat-mech↗

arXiv2010

Strongly correlated gases of Rydberg-dressed atoms: quantum and classical dynamics

We discuss techniques to generate long-range interactions in a gas of groundstate alkali atoms, by weakly admixing excited Rydberg states with laser light. This provides a tool to engineer strongly correlated phases with reduced decoherence from inelastic collisions and spontaneous emission. As an illustration, we discuss the quantum phases of dressed atoms with dipole-dipole interactions confined in a harmonic potential, as relevant to experiments. We show that residual spontaneous emission from the Rydberg state acts as a heating mechanism, leading to a quantum-classical crossover.

cond-mat.quant-gas↗

arXiv2009

Mesoscopic phases of dipolar ensembles with polar molecules and Rydberg atoms

We discuss the realization of mesoscopic phases of dipolar gases relevant to current experiments with cold polar molecules and Rydberg atoms confined to two dimensions. We predict the existence of superfluid clusters, mesoscopic supersolids, and crystals for a small number of trapped particles, with no counterpart in the homogeneous situation. For certain strengths of the dipole-dipole interactions, the stabilization of purely {\it non-classical crystals} by quantum fluctuations is possible. We propose a magnification scheme to detect the spatial structure of these crystalline phases.

cond-mat.quant-gas↗

arXiv2009

Quantum Simulations of Extended Hubbard Models with Dipolar Crystals

In this paper we study the realization of lattice models in mixtures of atomic and dipolar molecular quantum gases. We consider a situation where polar molecules form a self-assembled dipolar lattice, in which atoms or molecules of a second species can move and scatter. We describe the system dynamics in a master equation approach in the Brownian motion limit of slow particles and fast phonons, which we find appropriate for our system. In a wide regime of parameters, the reduced dynamics of the particles leads to physical realizations of extended Hubbard models with tuneable long-range interactions mediated by crystal phonons. This extends the notion of quantum simulation of strongly correlated systems with cold atoms and molecules to include phonon-dynamics, where all coupling parameters can be controlled by external fields.

cond-mat.other↗

arXiv2008

Trap modulation spectroscopy of the Mott-insulator transition in optical lattices

We introduce a new technique to probe the properties of an interacting cold atomic gas that can be viewed as a dynamical compressibility measurement. We apply this technique to the study of the superfluid to Mott insulator quantum phase transition in one and three dimensions for a bosonic gas trapped in an optical lattice. Excitations of the system are detected by time-of-flight measurements. The experimental data for the one-dimensional case are in good agreement with the results of a time-dependent density matrix renormalization group calculation.

cond-mat.other↗

arXiv2008

Three-body Interactions in one Dimension

We determine the phase-diagram of a one-dimensional system of hard-core lattice bosons interacting via repulsive three-body interactions by analytic methods and extensive quantum Monte-Carlo simulations. Such three-body interactions can be derived from a microscopic theory for polar molecules trapped in an optical lattice. Depending on the strength of the interactions and the particle density, we find superfluid and solid phases, the latter appearing at an unconventional filling of the lattice and displaying a coexistence of charge-density-wave and bond orders.

cond-mat.other↗

arXiv2008

State-dependent, addressable subwavelength lattices with cold atoms

We discuss how adiabatic potentials can be used to create addressable lattices on a subwavelength scale, which can be used as a tool for local operations and readout within a lattice substructure, while taking advantage of the faster timescales and higher energy and temperature scales determined by the shorter lattice spacing. For alkaline-earth-like atoms with non-zero nuclear spin, these potentials can be made state dependent, for which we give specific examples with $^{171}$Yb atoms. We discuss in detail the limitations in generating the lattice potentials, in particular non-adiabatic losses, and show that the loss rates can always be made exponentially small by increasing the laser power.

cond-mat.other↗

arXiv2008

Condensed Matter Physics with Cold Polar Molecules

In this review chapter we focus on the many-body dynamics of cold polar molecules in the strongly interacting regime. In particular, we discuss a toolbox for engineering many-body Hamiltonians based on the manipulation of the electric dipole moments of the molecules, and thus of molecular interactions, using external static and microwave fields. This forms the basis for the realization of novel quantum phases in these systems.

cond-mat.other↗