We study the motion of a superfluid vortex in condensates having different background density pro... more We study the motion of a superfluid vortex in condensates having different background density profiles, ranging from parabolic to uniform. The resulting effective point-vortex model for a generic power-law potential ∝ r k can be experimentally realized with recent advances in optical-trapping techniques. Our analysis encompasses both empty-core and filled-core vortices. In the latter case, the vortex acquires a mass due to the presence of distinguishable atoms located in its core. The axisymmetry allows us to reduce the coupled dynamical equations of motion to a single radial equation with an effective potential V eff. In many cases, V eff has a single minimum, where the vortex precesses uniformly. The dynamics of the vortex and the localized massive core arises from the dependence of the energy on the radial position of the vortex and from the r k trap potential. We find that a positive vortex with small mass orbits in the positive direction, but the sense of precession can reverse as the core mass increases. Early experiments and theoretical studies on two-component vortices found some qualitatively similar behavior.
In the present work we discuss inter-species entanglement in Bose-Bose mixtures trapped in optica... more In the present work we discuss inter-species entanglement in Bose-Bose mixtures trapped in optical lattices. This work is motivated by the observation that, in the presence of a second component, the Mott-insulator lobe shifts differently on the hole-and particle-side with respect to the Mott lobe of the single species system [1, 2]. We use perturbation theory, formulated in a Hilbert space decomposed by means of lattice symmetries, in order to show that the nonuniform shift of the Mott lobe is a consequence of an inter-species entanglement which differs in the lowest excited states to remove and add a particle. Our results indicate that inter-species entanglement in mixtures can provide a new perspective in understanding quantum phase transitions. To validate our approach, we compare our results from perturbation theory with quantum Monte Carlo simulations.
The stationary transverse laser patterns correspond to the minima of an appropriate generalized f... more The stationary transverse laser patterns correspond to the minima of an appropriate generalized free energy. The calculated patterns agree with the experimental observations at P.T.B. in Braunschweig, and display exotic structures called phase singularities.
We perform a numeric study (Worm algorithm Monte Carlo simulations) of ultracold twocomponent bos... more We perform a numeric study (Worm algorithm Monte Carlo simulations) of ultracold twocomponent bosons in two-dimensional optical lattices. We study how the Mott insulator to superfluid transition is affected by the presence of a second superfluid bosonic species. We find that, at fixed interspecies interaction, the upper and lower boundaries of the Mott lobe are differently modified. The lower boundary is strongly renormalized even for relatively low filling factor of the second component and moderate (interspecies) interaction. The upper boundary, instead, is affected only for large enough filling of the second component. Whereas boundaries are renormalized we find evidence of polaron-like excitations. Our results are of interest for current experimental setups.
A bosonic gas formed by two interacting species trapped in a double-well potential features macro... more A bosonic gas formed by two interacting species trapped in a double-well potential features macroscopic localization effects when the interspecies interaction becomes sufficiently strong. A repulsive interaction spatially separates the species into different wells while an attractive interaction confines both species in the same well. We perform a fully-analytic study of the transitions from the weak-to the strong-interaction regime by exploiting the semiclassical method in which boson populations are represented in terms of continuous variables. We find an explict description of low-energy eigenstates and spectrum in terms of the model parameters which includes the neighborhood of the transition point. To test the effectiveness of the continuous-variable method we compare its predictions with the exact results found numerically. Numerical calculations confirm the spectral collapse evidenced by this method when the space localization takes place.
We study the motion of superfluid vortices with filled massive cores. Previous point-vortex model... more We study the motion of superfluid vortices with filled massive cores. Previous point-vortex models already pointed out the impact of the core mass on the vortex dynamical properties, but relied on an assumption that is questionable in many physical systems where the immiscibility condition is barely satisfied: the fact that the massive core always lays at the very bottom of the effective confining potential constituted by the hosting vortex. Here, we relax this assumption and present a new point-vortex model where quantum vortices are harmonically coupled to their massive cores. We thoroughly explore the new dynamical regimes offered by this improved model; we then show that the functional dependence of the system normal modes on the microscopic parameters can be correctly interpreted only within this new generalized framework. Our predictions are benchmarked against the numerical simulations of coupled Gross-Pitaevskii equations for a realistic mixture of atomic Bose-Einstein condensates.
We show that, depending on the ratio between the inter-and the intra-species interactions, a bina... more We show that, depending on the ratio between the inter-and the intra-species interactions, a binary mixture trapped in a three-well potential with periodic boundary conditions exhibits three macroscopic ground-state configurations which differ in the degree of mixing. Accordingly, the corresponding quantum states feature either delocalization or a Schrödinger cat-like structure. The two-step phase separation occurring in the system, which is smoothed by the activation of tunnelling processes, is confirmed by the analysis of the energy spectrum that collapses and rearranges at the two critical points. In such points, we show that also Entanglement Entropy, a quantity borrowed from quantum-information theory, features singularities, thus demonstrating its ability to witness the double mixining-demixing phase transition. The developed analysis, which is of interest to both the experimental and theoretical communities, opens the door to the study of the demixing mechanism in complex lattice geometries.
Motivated by recent experiments and theoretical investigations on binary mixtures, we investigate... more Motivated by recent experiments and theoretical investigations on binary mixtures, we investigate the miscible-immiscible transition at finite temperature by means of Quantum Monte Carlo. Based on the observation that the segregated phase is strongly affected by temperature, we propose to use the degree of demixing for thermometry of a binary bosonic mixture trapped in an optical lattice. We show that the proposed method is especially sensitive at low temperatures, of the order of the tunnelling amplitude, and therefore is particularly suitable in the regime where quantum magnetism is expected. Ultracold atoms in optical lattices are generally regarded as an almost ideal experimental setting to investigate many-body quantum physics in strongly correlated regimes 1. However, next to undisputed strengths, atomic systems suffer from some notable limitations. Perhaps surprisingly if compared to condensed-matter counterparts, for strongly correlated quantum gases measuring fundamental parameters, such as temperature, is far from trivial, a fact often encumbering the comparison between theoretical and experimental findings. The physical reason is that the primary thermometric quantity used in cold atoms experiments, namely the momentum distribution, in strongly correlated regimes is often dominated by quantum rather than thermal fluctuations, thereby becoming quite insensitive to temperature variations. In recognition of its importance, thermometry for optical lattices have sparked numerous theoretical proposals and experiments 2. Quite generally, two main approaches have been pursued for thermometry: through ancillary samples (or sample subsets) in a well-understood, e.g. weakly interacting (WI), regime 3-7 ; or by measuring in-situ local density fluctuations with high-resolution imaging 8-13. Other proposed methods still await experimental demonstration 14-16. A new thermometric scheme. In this work, we propose a thermometry technique for ultracold quantum mixtures in optical lattices based on the demixing of two mutually repulsive components. Multi-components BECs have been created long ago 17, 18 , while recently seminal works in thermometry have been reported both with bosonic and fermionic samples. With a rubidium condensate, demixing between two spin components was induced by a magnetic field gradient and the width of the interface region was used to estimate the temperature 3, 4. Recently, the spin waves, or 'magnons', in a spinor Rb condensate were used to reduce the entropy per particle to values as low as 0.02 k B 19 , an order of magnitude below the values required for the onset of magnetic phases 20. On the fermionic side, anti-ferromagnetic correlations have been detected by means of Bragg scattering 21 , and also, very recently, directly by means of single-site imaging 22-24. We analyze the effect of temperature fluctuations on a demixed phase of a mixture of two bosonic species trapped in an optical lattice with and without an external harmonic confinement. Demixing, i.e. the spatial separation of the two components, occurs when inter-species repulsion overcomes the intra-species one 25-28. An important role is played by temperature fluctuations which compete with, and eventually destroy, demixing 29. Here, we take advantage of this competition to propose a route for thermometry in ultracold mixtures: we employ a suitable global estimator of demixing which can readily be measured and used to determine the temperature. We first consider the case of a moderately shallow optical lattice, where each species is superfluid. At sufficiently weak interspecies interaction, this regime is interesting as the momentum distribution of either species allows an independent determination of the temperature 30 to validate the currently proposed thermometry. In the case of a deeper optical lattice, thus a strongly-interacting (SI) regime 31 , we lack reliable temperature estimators other than the direct microscopic observation of particle-hole pairs. In this regime, our proposed thermometry proves a remarkably effective tool. Specifically, we show how the degree of demixing characterizing the spatial distribution of trapped mixtures depends upon the temperature. In particular,
Motivated by recent experiments and theoretical investigations on binary mixtures, we investigate... more Motivated by recent experiments and theoretical investigations on binary mixtures, we investigate the miscible-immiscible transition at finite temperature by means of Quantum Monte Carlo. Based on the observation that the segregated phase is strongly affected by temperature, we propose to use the degree of demixing for thermometry of a binary bosonic mixture trapped in an optical lattice. We show that the proposed method is especially sensitive at low temperatures, of the order of the tunnelling amplitude, and therefore is particularly suitable in the regime where quantum magnetism is expected. Ultracold atoms in optical lattices are generally regarded as an almost ideal experimental setting to investigate many-body quantum physics in strongly correlated regimes 1. However, next to undisputed strengths, atomic systems suffer from some notable limitations. Perhaps surprisingly if compared to condensed-matter counterparts, for strongly correlated quantum gases measuring fundamental parameters, such as temperature, is far from trivial, a fact often encumbering the comparison between theoretical and experimental findings. The physical reason is that the primary thermometric quantity used in cold atoms experiments, namely the momentum distribution, in strongly correlated regimes is often dominated by quantum rather than thermal fluctuations, thereby becoming quite insensitive to temperature variations. In recognition of its importance, thermometry for optical lattices have sparked numerous theoretical proposals and experiments 2. Quite generally, two main approaches have been pursued for thermometry: through ancillary samples (or sample subsets) in a well-understood, e.g. weakly interacting (WI), regime 3-7 ; or by measuring in-situ local density fluctuations with high-resolution imaging 8-13. Other proposed methods still await experimental demonstration 14-16. A new thermometric scheme. In this work, we propose a thermometry technique for ultracold quantum mixtures in optical lattices based on the demixing of two mutually repulsive components. Multi-components BECs have been created long ago 17, 18 , while recently seminal works in thermometry have been reported both with bosonic and fermionic samples. With a rubidium condensate, demixing between two spin components was induced by a magnetic field gradient and the width of the interface region was used to estimate the temperature 3, 4. Recently, the spin waves, or 'magnons' , in a spinor Rb condensate were used to reduce the entropy per particle to values as low as 0.02 k B 19
We consider the dynamical properties of quantum vortices with filled massive cores, hence the ter... more We consider the dynamical properties of quantum vortices with filled massive cores, hence the term "massive vortices". While the motion of massless vortices is described by firstorder motion equations, the inclusion of core mass introduces a second-order time derivative in the motion equations and thus doubles the number of independent dynamical variables needed to describe the vortex. The simplest possible system where this physics is present, i.e. a single massive vortex in a circular domain, is thoroughly discussed. We point out that a massive vortex can exhibit various dynamical regimes, as opposed to its massless counterpart, which can only precess at a constant rate. The predictions of our analytical model are validated by means of numerical simulations of coupled Gross-Pitaevskii equations, which indeed display the signature of the core inertial mass. Eventually, we discuss a nice formal analogy between the motion of massive vortices and that of massive charges in two-dimensional domains pierced by magnetic fields.
We study interacting dipolar atomic bosons in a triple-well potential within a ring geometry. Thi... more We study interacting dipolar atomic bosons in a triple-well potential within a ring geometry. This system is shown to be equivalent to a three-site Bose-Hubbard model. We analyze the ground state of dipolar bosons by varying the effective on-site interaction. This analysis is performed both numerically and analytically by using suitable coherent-state representations of the ground state. The latter exhibits a variety of forms ranging from the su(3) coherent state in the delocalization regime to a macroscopic cat-like state with fully localized populations, passing for a coexistence regime where the ground state displays a mixed character. We characterize the quantum correlations of the ground state from the bi-partition perspective. We calculate both numerically and analytically (within the previous coherent-state representation) the single-site entanglement entropy which, among various interesting properties, exhibits a maximum value in correspondence to the transition from the cat-like to the coexistence regime. In the latter case, we show that the ground-state mixed form corresponds, semiclassically, to an energy exhibiting two almost-degenerate minima.
We study the motion of a superfluid vortex in condensates having different background density pro... more We study the motion of a superfluid vortex in condensates having different background density profiles, ranging from parabolic to uniform. The resulting effective point-vortex model for a generic power-law potential ∝ r k can be experimentally realized with recent advances in optical-trapping techniques. Our analysis encompasses both empty-core and filled-core vortices. In the latter case, the vortex acquires a mass due to the presence of distinguishable atoms located in its core. The axisymmetry allows us to reduce the coupled dynamical equations of motion to a single radial equation with an effective potential V eff. In many cases, V eff has a single minimum, where the vortex precesses uniformly. The dynamics of the vortex and the localized massive core arises from the dependence of the energy on the radial position of the vortex and from the r k trap potential. We find that a positive vortex with small mass orbits in the positive direction, but the sense of precession can reverse as the core mass increases. Early experiments and theoretical studies on two-component vortices found some qualitatively similar behavior.
Submitted for the DAMOP14 Meeting of The American Physical Society Mott-insulator to superfluid t... more Submitted for the DAMOP14 Meeting of The American Physical Society Mott-insulator to superfluid transition in the strong coupling regime and in the presence of a minority component WEI WANG, BAR-BARA CAPOGROSSO-SANSONE, Univ of Oklahoma, VITTORIO PENNA, Depat. of applied science, Politecnico of Torino-By means of perturbation theory, we study the Mott-insulator to superfluid transition in the strong coupling regime and in the presence of a minority second component. In the limit of zero hopping, ground-states are in general degenerate. This degeneracy is not always lifted by the first order perturbation theory. In such cases, the standard perturbation theory does not uniquely determine the ground-state correction. To resolve this issue, we proved that the ground state energy of the Hamiltonian is non-degenerate, and used this property along with symmetry properties of the lattice to determine the first order correction to the ground state.
Quantum dynamics of impurities in a bath of bosons is a long-standing problem in solid-state, pla... more Quantum dynamics of impurities in a bath of bosons is a long-standing problem in solid-state, plasma, and atomic physics. Recent experimental and theoretical investigations with ultracold atoms have focused on this problem, studying atomic impurities immersed in an atomic Bose-Einstein condensate (BEC) and for various relative coupling strengths tuned by the Fano−Feshbach resonance technique. Here, we report extensive numerical simulations on a closely related problem: the collision between a bosonic impurity consisting of a few 41 K atoms and a BEC of 87 Rb atoms in a quasi onedimensional configuration and under a weak harmonic axial confinement. For small values of the inter-species interaction strength (regardless of its sign), we find that the impurity, which starts from outside the BEC, simply causes the BEC cloud to oscillate back and forth, but the frequency of oscillation depends on the interaction strength. For intermediate couplings, after a few cycles of oscillation the impurity is captured by the BEC, and strongly changes its amplitude of oscillation. In the strong interaction regime, if the inter-species interaction is attractive, a local maximum (bright soliton) in the BEC density occurs where the impurity is trapped; if, instead, the inter-species interaction is repulsive, the impurity is not able to enter the BEC cloud and the reflection coefficient is close to one. However, if the initial displacement of the impurity is increased, the impurity is able to penetrate the cloud, leading to the appearance of a moving hole (dark soliton) in the BEC.
We study the motion of a superfluid vortex in condensates having different background density pro... more We study the motion of a superfluid vortex in condensates having different background density profiles, ranging from parabolic to uniform. The resulting effective point-vortex model for a generic power-law potential ∝ r k can be experimentally realized with recent advances in optical-trapping techniques. Our analysis encompasses both empty-core and filled-core vortices. In the latter case, the vortex acquires a mass due to the presence of distinguishable atoms located in its core. The axisymmetry allows us to reduce the coupled dynamical equations of motion to a single radial equation with an effective potential V eff. In many cases, V eff has a single minimum, where the vortex precesses uniformly. The dynamics of the vortex and the localized massive core arises from the dependence of the energy on the radial position of the vortex and from the r k trap potential. We find that a positive vortex with small mass orbits in the positive direction, but the sense of precession can reverse as the core mass increases. Early experiments and theoretical studies on two-component vortices found some qualitatively similar behavior.
In the present work we discuss inter-species entanglement in Bose-Bose mixtures trapped in optica... more In the present work we discuss inter-species entanglement in Bose-Bose mixtures trapped in optical lattices. This work is motivated by the observation that, in the presence of a second component, the Mott-insulator lobe shifts differently on the hole-and particle-side with respect to the Mott lobe of the single species system [1, 2]. We use perturbation theory, formulated in a Hilbert space decomposed by means of lattice symmetries, in order to show that the nonuniform shift of the Mott lobe is a consequence of an inter-species entanglement which differs in the lowest excited states to remove and add a particle. Our results indicate that inter-species entanglement in mixtures can provide a new perspective in understanding quantum phase transitions. To validate our approach, we compare our results from perturbation theory with quantum Monte Carlo simulations.
The stationary transverse laser patterns correspond to the minima of an appropriate generalized f... more The stationary transverse laser patterns correspond to the minima of an appropriate generalized free energy. The calculated patterns agree with the experimental observations at P.T.B. in Braunschweig, and display exotic structures called phase singularities.
We perform a numeric study (Worm algorithm Monte Carlo simulations) of ultracold twocomponent bos... more We perform a numeric study (Worm algorithm Monte Carlo simulations) of ultracold twocomponent bosons in two-dimensional optical lattices. We study how the Mott insulator to superfluid transition is affected by the presence of a second superfluid bosonic species. We find that, at fixed interspecies interaction, the upper and lower boundaries of the Mott lobe are differently modified. The lower boundary is strongly renormalized even for relatively low filling factor of the second component and moderate (interspecies) interaction. The upper boundary, instead, is affected only for large enough filling of the second component. Whereas boundaries are renormalized we find evidence of polaron-like excitations. Our results are of interest for current experimental setups.
A bosonic gas formed by two interacting species trapped in a double-well potential features macro... more A bosonic gas formed by two interacting species trapped in a double-well potential features macroscopic localization effects when the interspecies interaction becomes sufficiently strong. A repulsive interaction spatially separates the species into different wells while an attractive interaction confines both species in the same well. We perform a fully-analytic study of the transitions from the weak-to the strong-interaction regime by exploiting the semiclassical method in which boson populations are represented in terms of continuous variables. We find an explict description of low-energy eigenstates and spectrum in terms of the model parameters which includes the neighborhood of the transition point. To test the effectiveness of the continuous-variable method we compare its predictions with the exact results found numerically. Numerical calculations confirm the spectral collapse evidenced by this method when the space localization takes place.
We study the motion of superfluid vortices with filled massive cores. Previous point-vortex model... more We study the motion of superfluid vortices with filled massive cores. Previous point-vortex models already pointed out the impact of the core mass on the vortex dynamical properties, but relied on an assumption that is questionable in many physical systems where the immiscibility condition is barely satisfied: the fact that the massive core always lays at the very bottom of the effective confining potential constituted by the hosting vortex. Here, we relax this assumption and present a new point-vortex model where quantum vortices are harmonically coupled to their massive cores. We thoroughly explore the new dynamical regimes offered by this improved model; we then show that the functional dependence of the system normal modes on the microscopic parameters can be correctly interpreted only within this new generalized framework. Our predictions are benchmarked against the numerical simulations of coupled Gross-Pitaevskii equations for a realistic mixture of atomic Bose-Einstein condensates.
We show that, depending on the ratio between the inter-and the intra-species interactions, a bina... more We show that, depending on the ratio between the inter-and the intra-species interactions, a binary mixture trapped in a three-well potential with periodic boundary conditions exhibits three macroscopic ground-state configurations which differ in the degree of mixing. Accordingly, the corresponding quantum states feature either delocalization or a Schrödinger cat-like structure. The two-step phase separation occurring in the system, which is smoothed by the activation of tunnelling processes, is confirmed by the analysis of the energy spectrum that collapses and rearranges at the two critical points. In such points, we show that also Entanglement Entropy, a quantity borrowed from quantum-information theory, features singularities, thus demonstrating its ability to witness the double mixining-demixing phase transition. The developed analysis, which is of interest to both the experimental and theoretical communities, opens the door to the study of the demixing mechanism in complex lattice geometries.
Motivated by recent experiments and theoretical investigations on binary mixtures, we investigate... more Motivated by recent experiments and theoretical investigations on binary mixtures, we investigate the miscible-immiscible transition at finite temperature by means of Quantum Monte Carlo. Based on the observation that the segregated phase is strongly affected by temperature, we propose to use the degree of demixing for thermometry of a binary bosonic mixture trapped in an optical lattice. We show that the proposed method is especially sensitive at low temperatures, of the order of the tunnelling amplitude, and therefore is particularly suitable in the regime where quantum magnetism is expected. Ultracold atoms in optical lattices are generally regarded as an almost ideal experimental setting to investigate many-body quantum physics in strongly correlated regimes 1. However, next to undisputed strengths, atomic systems suffer from some notable limitations. Perhaps surprisingly if compared to condensed-matter counterparts, for strongly correlated quantum gases measuring fundamental parameters, such as temperature, is far from trivial, a fact often encumbering the comparison between theoretical and experimental findings. The physical reason is that the primary thermometric quantity used in cold atoms experiments, namely the momentum distribution, in strongly correlated regimes is often dominated by quantum rather than thermal fluctuations, thereby becoming quite insensitive to temperature variations. In recognition of its importance, thermometry for optical lattices have sparked numerous theoretical proposals and experiments 2. Quite generally, two main approaches have been pursued for thermometry: through ancillary samples (or sample subsets) in a well-understood, e.g. weakly interacting (WI), regime 3-7 ; or by measuring in-situ local density fluctuations with high-resolution imaging 8-13. Other proposed methods still await experimental demonstration 14-16. A new thermometric scheme. In this work, we propose a thermometry technique for ultracold quantum mixtures in optical lattices based on the demixing of two mutually repulsive components. Multi-components BECs have been created long ago 17, 18 , while recently seminal works in thermometry have been reported both with bosonic and fermionic samples. With a rubidium condensate, demixing between two spin components was induced by a magnetic field gradient and the width of the interface region was used to estimate the temperature 3, 4. Recently, the spin waves, or 'magnons', in a spinor Rb condensate were used to reduce the entropy per particle to values as low as 0.02 k B 19 , an order of magnitude below the values required for the onset of magnetic phases 20. On the fermionic side, anti-ferromagnetic correlations have been detected by means of Bragg scattering 21 , and also, very recently, directly by means of single-site imaging 22-24. We analyze the effect of temperature fluctuations on a demixed phase of a mixture of two bosonic species trapped in an optical lattice with and without an external harmonic confinement. Demixing, i.e. the spatial separation of the two components, occurs when inter-species repulsion overcomes the intra-species one 25-28. An important role is played by temperature fluctuations which compete with, and eventually destroy, demixing 29. Here, we take advantage of this competition to propose a route for thermometry in ultracold mixtures: we employ a suitable global estimator of demixing which can readily be measured and used to determine the temperature. We first consider the case of a moderately shallow optical lattice, where each species is superfluid. At sufficiently weak interspecies interaction, this regime is interesting as the momentum distribution of either species allows an independent determination of the temperature 30 to validate the currently proposed thermometry. In the case of a deeper optical lattice, thus a strongly-interacting (SI) regime 31 , we lack reliable temperature estimators other than the direct microscopic observation of particle-hole pairs. In this regime, our proposed thermometry proves a remarkably effective tool. Specifically, we show how the degree of demixing characterizing the spatial distribution of trapped mixtures depends upon the temperature. In particular,
Motivated by recent experiments and theoretical investigations on binary mixtures, we investigate... more Motivated by recent experiments and theoretical investigations on binary mixtures, we investigate the miscible-immiscible transition at finite temperature by means of Quantum Monte Carlo. Based on the observation that the segregated phase is strongly affected by temperature, we propose to use the degree of demixing for thermometry of a binary bosonic mixture trapped in an optical lattice. We show that the proposed method is especially sensitive at low temperatures, of the order of the tunnelling amplitude, and therefore is particularly suitable in the regime where quantum magnetism is expected. Ultracold atoms in optical lattices are generally regarded as an almost ideal experimental setting to investigate many-body quantum physics in strongly correlated regimes 1. However, next to undisputed strengths, atomic systems suffer from some notable limitations. Perhaps surprisingly if compared to condensed-matter counterparts, for strongly correlated quantum gases measuring fundamental parameters, such as temperature, is far from trivial, a fact often encumbering the comparison between theoretical and experimental findings. The physical reason is that the primary thermometric quantity used in cold atoms experiments, namely the momentum distribution, in strongly correlated regimes is often dominated by quantum rather than thermal fluctuations, thereby becoming quite insensitive to temperature variations. In recognition of its importance, thermometry for optical lattices have sparked numerous theoretical proposals and experiments 2. Quite generally, two main approaches have been pursued for thermometry: through ancillary samples (or sample subsets) in a well-understood, e.g. weakly interacting (WI), regime 3-7 ; or by measuring in-situ local density fluctuations with high-resolution imaging 8-13. Other proposed methods still await experimental demonstration 14-16. A new thermometric scheme. In this work, we propose a thermometry technique for ultracold quantum mixtures in optical lattices based on the demixing of two mutually repulsive components. Multi-components BECs have been created long ago 17, 18 , while recently seminal works in thermometry have been reported both with bosonic and fermionic samples. With a rubidium condensate, demixing between two spin components was induced by a magnetic field gradient and the width of the interface region was used to estimate the temperature 3, 4. Recently, the spin waves, or 'magnons' , in a spinor Rb condensate were used to reduce the entropy per particle to values as low as 0.02 k B 19
We consider the dynamical properties of quantum vortices with filled massive cores, hence the ter... more We consider the dynamical properties of quantum vortices with filled massive cores, hence the term "massive vortices". While the motion of massless vortices is described by firstorder motion equations, the inclusion of core mass introduces a second-order time derivative in the motion equations and thus doubles the number of independent dynamical variables needed to describe the vortex. The simplest possible system where this physics is present, i.e. a single massive vortex in a circular domain, is thoroughly discussed. We point out that a massive vortex can exhibit various dynamical regimes, as opposed to its massless counterpart, which can only precess at a constant rate. The predictions of our analytical model are validated by means of numerical simulations of coupled Gross-Pitaevskii equations, which indeed display the signature of the core inertial mass. Eventually, we discuss a nice formal analogy between the motion of massive vortices and that of massive charges in two-dimensional domains pierced by magnetic fields.
We study interacting dipolar atomic bosons in a triple-well potential within a ring geometry. Thi... more We study interacting dipolar atomic bosons in a triple-well potential within a ring geometry. This system is shown to be equivalent to a three-site Bose-Hubbard model. We analyze the ground state of dipolar bosons by varying the effective on-site interaction. This analysis is performed both numerically and analytically by using suitable coherent-state representations of the ground state. The latter exhibits a variety of forms ranging from the su(3) coherent state in the delocalization regime to a macroscopic cat-like state with fully localized populations, passing for a coexistence regime where the ground state displays a mixed character. We characterize the quantum correlations of the ground state from the bi-partition perspective. We calculate both numerically and analytically (within the previous coherent-state representation) the single-site entanglement entropy which, among various interesting properties, exhibits a maximum value in correspondence to the transition from the cat-like to the coexistence regime. In the latter case, we show that the ground-state mixed form corresponds, semiclassically, to an energy exhibiting two almost-degenerate minima.
We study the motion of a superfluid vortex in condensates having different background density pro... more We study the motion of a superfluid vortex in condensates having different background density profiles, ranging from parabolic to uniform. The resulting effective point-vortex model for a generic power-law potential ∝ r k can be experimentally realized with recent advances in optical-trapping techniques. Our analysis encompasses both empty-core and filled-core vortices. In the latter case, the vortex acquires a mass due to the presence of distinguishable atoms located in its core. The axisymmetry allows us to reduce the coupled dynamical equations of motion to a single radial equation with an effective potential V eff. In many cases, V eff has a single minimum, where the vortex precesses uniformly. The dynamics of the vortex and the localized massive core arises from the dependence of the energy on the radial position of the vortex and from the r k trap potential. We find that a positive vortex with small mass orbits in the positive direction, but the sense of precession can reverse as the core mass increases. Early experiments and theoretical studies on two-component vortices found some qualitatively similar behavior.
Submitted for the DAMOP14 Meeting of The American Physical Society Mott-insulator to superfluid t... more Submitted for the DAMOP14 Meeting of The American Physical Society Mott-insulator to superfluid transition in the strong coupling regime and in the presence of a minority component WEI WANG, BAR-BARA CAPOGROSSO-SANSONE, Univ of Oklahoma, VITTORIO PENNA, Depat. of applied science, Politecnico of Torino-By means of perturbation theory, we study the Mott-insulator to superfluid transition in the strong coupling regime and in the presence of a minority second component. In the limit of zero hopping, ground-states are in general degenerate. This degeneracy is not always lifted by the first order perturbation theory. In such cases, the standard perturbation theory does not uniquely determine the ground-state correction. To resolve this issue, we proved that the ground state energy of the Hamiltonian is non-degenerate, and used this property along with symmetry properties of the lattice to determine the first order correction to the ground state.
Quantum dynamics of impurities in a bath of bosons is a long-standing problem in solid-state, pla... more Quantum dynamics of impurities in a bath of bosons is a long-standing problem in solid-state, plasma, and atomic physics. Recent experimental and theoretical investigations with ultracold atoms have focused on this problem, studying atomic impurities immersed in an atomic Bose-Einstein condensate (BEC) and for various relative coupling strengths tuned by the Fano−Feshbach resonance technique. Here, we report extensive numerical simulations on a closely related problem: the collision between a bosonic impurity consisting of a few 41 K atoms and a BEC of 87 Rb atoms in a quasi onedimensional configuration and under a weak harmonic axial confinement. For small values of the inter-species interaction strength (regardless of its sign), we find that the impurity, which starts from outside the BEC, simply causes the BEC cloud to oscillate back and forth, but the frequency of oscillation depends on the interaction strength. For intermediate couplings, after a few cycles of oscillation the impurity is captured by the BEC, and strongly changes its amplitude of oscillation. In the strong interaction regime, if the inter-species interaction is attractive, a local maximum (bright soliton) in the BEC density occurs where the impurity is trapped; if, instead, the inter-species interaction is repulsive, the impurity is not able to enter the BEC cloud and the reflection coefficient is close to one. However, if the initial displacement of the impurity is increased, the impurity is able to penetrate the cloud, leading to the appearance of a moving hole (dark soliton) in the BEC.
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Papers by Vittorio Penna