arXiv subjects

Guido Pupillo

Publications and source records attributed to Guido Pupillo.

At least 91 records · Page 5Linked to original sources

arXiv2014

Transmissive optomechanical platforms with engineered spatial defects

We investigate the optomechanical photon-phonon coupling of a single light mode propagating through an array of vibrating mechanical elements. As recently shown for the particular case of a periodic array of membranes embedded in a high-finesse optical cavity [A. Xuereb, C. Genes and A. Dantan, Phys. Rev. Lett., \textbf{109}, 223601, (2012)], the intracavity linear optomechanical coupling can be considerably enhanced over the single element value in the so-called \textit{transmissive regime}, where for motionless membranes the whole system is transparent to light. Here, we extend these investigations to quasi-periodic arrays in the presence of engineered spatial defects in the membrane positions. In particular we show that the localization of light modes induced by the defect combined with the access of the transmissive regime window can lead to additional enhancement of the strength of both linear and quadratic optomechanical couplings.

quant-ph↗

arXiv2014

Reconfigurable long-range phonon dynamics in optomechanical arrays

We investigate periodic optomechanical arrays as reconfigurable platforms for engineering the coupling between multiple mechanical and electromagnetic modes and for exploring many-body phonon dynamics. Exploiting structural resonances in the coupling between light fields and collective motional modes of the array, we show that tunable effective long-range interactions between mechanical modes can be achieved. This paves the way towards the implementation of controlled phononic walks and heat transfer on densely-connected graphs as well as the coherent transfer of excitations between distant elements of optomechanical arrays.

quant-ph↗

arXiv2014

Defect-induced supersolidity with soft-core bosons

More than 40 years ago, Andreev, Lifshitz, and Chester suggested the possible existence of a peculiar solid phase of matter, the microscopic constituents of which can flow superfluidly without resistance due to the formation of zero-point defects in the ground state of self-assembled crystals. Yet, a physical system where this mechanism is unambiguously established remains to be found, both experimentally and theoretically. Here we investigate the zero-temperature phase diagram of two-dimensional bosons with finite-range soft-core interactions. For low particle densities, the system is show to feature a solid phase in which zero-point vacancies emerge spontaneously and give rice to superfluid flow of particles through the crystal. This provides the first example of defects-induced, continuous-space supersolidity consistent with the Andreev-Lifshitz-Chester scenario.

cond-mat.quant-gas↗

arXiv2013

Enhanced optomechanical readout using optical coalescence

We present a scheme to strongly enhance the readout sensitivity of the squared displacement of a mobile scatterer placed in a Fabry-Pérot cavity. We investigate the largely unexplored regime of cavity electrodynamics in which a highly reflective element positioned between the end mirrors of a symmetric Fabry-Pérot resonator strongly modifies the cavity response function, such that two longitudinal modes with different spatial parity are brought close to frequency degeneracy and interfere in the cavity output field. In the case of a movable middle reflector we show that the interference in this generic "optical coalescence" phenomenon gives rise to an enhanced frequency shift of the peaks of the cavity transmission that can be exploited in optomechanics.

quant-ph↗

arXiv2013

Cluster Luttinger Liquids of Rydberg-dressed Atoms in Optical Lattices

We investigate the zero-temperature phases of bosonic and fermionic gases confined to one dimension and interacting via a class of finite-range soft-shoulder potentials (i.e. soft-core potentials with an additional hard-core onsite interaction). Using a combination of analytical and numerical methods, we demonstrate the stabilization of critical quantum liquids with qualitatively new features with respect to the Tomonaga-Luttinger liquid paradigm. These features result from frustration and cluster formation in the corresponding classical ground-state. Characteristic signatures of these liquids are accessible in state-of-the-art experimental setups with Rydberg-dressed ground-state atoms trapped in optical lattices.

cond-mat.quant-gas↗

arXiv2013

Fluctuation-Dissipation Theorem in an Isolated System of Quantum Dipolar Bosons after a Quench

We examine the validity of fluctuation-dissipation relations in isolated quantum systems taken out of equilibrium by a sudden quench. We focus on the dynamics of trapped hard-core bosons in one-dimensional lattices with dipolar interactions whose strength is changed during the quench. We find that fluctuation-dissipation relations hold if the system is nonintegrable after the quench. They also hold if the system is integrable after the quench if the initial state is an equilibrium state of a nonintegrable Hamiltonian. However, they fail if the system is integrable both before and after quenching.

cond-mat.stat-mech↗

arXiv2012

Quantum Phases of Dipolar Bosons in Bilayer Geometry

We investigate the quantum phases of hard-core dipolar bosons confined to a square lattice in a bilayer geometry. Using exact theoretical techniques, we discuss the many-body effects resulting from pairing of particles across layers at finite density, including a novel pair supersolid phase, superfluid and solid phases. These results are of direct relevance to experiments with polar molecules and atoms with large magnetic dipole moments trapped in optical lattices.

cond-mat.quant-gas↗

arXiv2011

Atomic Rydberg Reservoirs for Polar Molecules

We discuss laser dressed dipolar and Van der Waals interactions between atoms and polar molecules, so that a cold atomic gas with laser admixed Rydberg levels acts as a designed reservoir for both elastic and inelastic collisional processes. The elastic scattering channel is characterized by large elastic scattering cross sections and repulsive shields to protect from close encounter collisions. In addition, we discuss a dissipative (inelastic) collision where a spontaneously emitted photon carries away (kinetic) energy of the collision partners, thus providing a significant energy loss in a single collision. This leads to the scenario of rapid thermalization and cooling of a molecule in the mK down to the μK regime by cold atoms.

physics.atom-ph↗

arXiv2011

Three-body correlation functions and recombination rates for bosons in three and one dimensions

We investigate local three-body correlations for bosonic particles in three and one dimensions as a function of the interaction strength. The three-body correlation function g(3) is determined by measuring the three-body recombination rate in an ultracold gas of Cs atoms. In three dimensions, we measure the dependence of g(3) on the gas parameter in a BEC, finding good agreement with the theoretical prediction accounting for beyond-mean-field effects. In one dimension, we observe a reduction of g(3) by several orders of magnitude upon increasing interactions from the weakly interacting BEC to the strongly interacting Tonks-Girardeau regime, in good agreement with predictions from the Lieb-Liniger model for all strengths of interaction.

cond-mat.quant-gas↗

arXiv2010

Realization of an Excited, Strongly-Correlated Quantum Gas Phase

Ultracold atomic physics offers myriad possibilities to study strongly correlated many-body systems in lower dimensions. Typically, only ground state phases are accessible. Using a tunable quantum gas of bosonic cesium atoms, we realize and control in one dimensional geometry a highly excited quantum phase that is stabilized in the presence of attractive interactions by maintaining and strengthening quantum correlations across a confinement-induced resonance. We diagnose the crossover from repulsive to attractive interactions in terms of the stiffness and the energy of the system. Our results open up the experimental study of metastable excited many-body phases with strong correlations and their dynamical properties.

cond-mat.quant-gas↗

arXiv2010

Universal rates for reactive ultracold polar molecules in reduced dimensions

Analytic expressions describe universal elastic and reactive rates of quasi-two-dimensional and quasi-one-dimensional collisions of highly reactive ultracold molecules interacting by a van der Waals potential. Exact and approximate calculations for the example species of KRb show that stability and evaporative cooling can be realized for spin-polarized fermions at moderate dipole and trapping strength, whereas bosons or unlike fermions require significantly higher dipole or trapping strengths.

physics.atom-ph↗

arXiv2010

Pinning quantum phase transition for a Luttinger liquid of strongly interacting bosons

One of the most remarkable results of quantum mechanics is the fact that many-body quantum systems may exhibit phase transitions even at zero temperature. Quantum fluctuations, deeply rooted in Heisenberg's uncertainty principle, and not thermal fluctuations, drive the system from one phase to another. Typically, the relative strength of two competing terms in the system's Hamiltonian is changed across a finite critical value. A well-known example is the Mott-Hubbard quantum phase transition from a superfluid to an insulating phase, which has been observed for weakly interacting bosonic atomic gases. However, for strongly interacting quantum systems confined to lower-dimensional geometry a novel type of quantum phase transition may be induced for which an arbitrarily weak perturbation to the Hamiltonian is sufficient to drive the transition. Here, for a one-dimensional (1D) quantum gas of bosonic caesium atoms with tunable interactions, we observe the commensurate-incommensurate quantum phase transition from a superfluid Luttinger liquid to a Mott-insulator. For sufficiently strong interactions, the transition is induced by adding an arbitrarily weak optical lattice commensurate with the atomic granularity, which leads to immediate pinning of the atoms. We map out the phase diagram and find that our measurements in the strongly interacting regime agree well with a quantum field description based on the exactly solvable sine-Gordon model. We trace the phase boundary all the way to the weakly interacting regime where we find good agreement with the predictions of the 1D Bose-Hubbard model. Our results open up the experimental study of quantum phase transitions, criticality, and transport phenomena beyond Hubbard-type models in the context of ultracold gases.

cond-mat.quant-gas↗

arXiv2010

Time-dependent currents of 1D bosons in an optical lattice

We analyse the time-dependence of currents in a 1D Bose gas in an optical lattice. For a 1D system, the stability of currents induced by accelerating the lattice exhibits a broad crossover as a function of the magnitude of the acceleration, and the strength of the inter-particle interactions. This differs markedly from mean-field results in higher dimensions. Using the infinite Time Evolving Block Decimation algorithm, we characterise this crossover by making quantitative predictions for the time-dependent behaviour of the currents and their decay rate. We also compute the time-dependence of quasi-condensate fractions which can be measured directly in experiments. We compare our results to calculations based on phase-slip methods, finding agreement with the scaling as the particle density increases, but with significant deviations near unit filling.

cond-mat.quant-gas↗

arXiv2008

Dipole oscillations of confined lattice bosons in one dimension

We study the dynamics of a non-integrable system comprising interacting cold bosons trapped in an optical lattice in one-dimension by means of exact time-dependent numerical DMRG techniques. Particles are confined by a parabolic potential, and dipole oscillations are induced by displacing the trap center of a few lattice sites. Depending on the system parameters this motion can vary from undamped to overdamped. We study the dipole oscillations as a function of the lattice displacement, the particle density and the strength of interparticle interactions. These results explain the recent experiment C.D. Fertig et al., Phys. Rev. Lett. 94, 120403 (2005).

cond-mat.other↗

arXiv2008

Structure and melting behavior of classical bilayer crystals of dipoles

We study the structure and melting of a classical bilayer system of dipoles, in a setup where the dipoles are oriented perpendicular to the planes of the layers and the density of dipoles is the same in each layer. Due to the anisotropic character of the dipole-dipole interactions, we find that the ground-state configuration is given by two hexagonal crystals positioned on top of each other, independent of the interlayer spacing and dipolar density. For large interlayer distances these crystals are independent, while in the opposite limit of small interlayer distances the system behaves as a two-dimensional crystal of paired dipoles. Within the harmonic approximation for the phonon excitations, the melting temperature of these crystalline configurations displays a non-monotonic dependence on the interlayer distance, which is associated with a re-entrant melting behavior in the form of solid-liquid-solid-liquid transitions at fixed temperature.

cond-mat.other↗

arXiv2006

The role of interactions, tunneling and harmonic confinement on the adiabatic loading of bosons in an optical lattice

We calculate entropy-temperature curves for interacting bosons in unit filled optical lattices for both homogeneous and harmonically trapped situations, and use them to understand how adiabatic changes in the lattice depth affect the temperature of the system. In a translationally invariant lattice, the zero tunneling limit facilitates a rather detailed analytic description. Unlike the non-interacting bosonic system which is always cooled upon adiabatic loading for low enough initial temperature, the change in the excitation spectrum induced by interactions can lead to heating. Finite tunneling helps to reduce this heating. Finally, we study the spatially inhomogeneous system confined in a parabolic potential and show that the presence of the trap can significantly reduce the final available temperature, due to the non-vanishing superfluid component at the edge of the cloud which is present in trapped systems.

cond-mat.stat-mech↗

arXiv2006

Bragg spectroscopy of trapped one dimensional strongly interacting bosons in optical lattices: Probing the cake-structure

We study Bragg spectroscopy of strongly interacting one dimensional bosons loaded in an optical lattice plus an additional parabolic potential. We calculate the dynamic structure factor by using Monte Carlo simulations for the Bose-Hubbard Hamiltonian, exact diagonalizations and the results of a recently introduced effective fermionization (EF) model. We find that, due to the system's inhomogeneity, the excitation spectrum exhibits a multi-branched structure, whose origin is related to the presence of superfluid regions with different densities in the atomic distribution. We thus suggest that Bragg spectroscopy in the linear regime can be used as an experimental tool to unveil the shell structure of alternating Mott insulator and superfluid phases characteristic of trapped bosons.

cond-mat.other↗

arXiv2006

Effects of finite temperature on the Mott insulator state

We investigate the effects of finite temperature on ultracold Bose atoms confined in an optical lattice plus a parabolic potential in the Mott insulator state. In particular, we analyze the temperature dependence of the density distribution of atomic pairs in the lattice, by means of exact Monte-Carlo simulations. We introduce a simple model that quantitatively accounts for the computed pair density distributions at low enough temperatures. We suggest that the temperature dependence of the atomic pair statistics may be used to estimate the system's temperature at energies of the order of the atoms' interaction energy.

cond-mat.other↗