Chiara D'Errico - Academia.edu (original) (raw)

Papers by Chiara D'Errico

Research paper thumbnail of Atom Interferometry with a Weakly Interacting Bose-Einstein Condensate

Bose-Einstein condensates have long been considered the most appropriate source for interferometr... more Bose-Einstein condensates have long been considered the most appropriate source for interferometry with matter waves, due to their maximal coherence properties. However, the realization of practical interferometers with condensates has been so far hindered by the presence of the natural atom-atom interaction, which dramatically affects their performance. We describe here the realization of a lattice-based interferometer based on a Bose-Einstein condensate where the contact interaction can be tuned by means of a Feshbach resonance, and eventually reduced towards zero. We observe a strong increase of the coherence time of the interferometer with vanishing scattering length, and see evidence of the effect of the weak magnetic dipole-dipole interaction. Our observations indicate that high-sensitivity atom interferometry with Bose-Einstein condensates is feasible, via a precise control of the interactions.

Research paper thumbnail of Magnetic dipolar interaction in an atomic Bose Einstein condensate interferometer

Physical Review Letters, 2008

We study the role played by the magnetic dipole interaction in an atomic interferometer based on ... more We study the role played by the magnetic dipole interaction in an atomic interferometer based on an alkali Bose-Einstein condensate with tunable scattering length. We tune the s-wave interaction to zero using a magnetic Feshbach resonance and measure the decoherence of the interferometer induced by the weak residual interaction between the magnetic dipoles of the atoms. We prove that with a proper choice of the scattering length it is possible to compensate for the dipolar interaction and extend the coherence time of the interferometer. We put in evidence the anisotropic character of the dipolar interaction by working with two different experimental configurations for which the minima of decoherence are achieved for a positive and a negative value of the scattering length, respectively. Our results are supported by a theoretical model we develop. This model indicates that the magnetic dipole interaction should not represent a serious source of decoherence in atom interferometers based on Bose-Einstein condensates.

Research paper thumbnail of Observation of an Efimov spectrum in an atomic system

In 1970 the Russian physicist V. Efimov predicted a puzzling quantum mechanical effect that is st... more In 1970 the Russian physicist V. Efimov predicted a puzzling quantum mechanical effect that is still of great interest today. He found that three particles subjected to a resonant pairwise interaction can join into an infinite number of loosely bound states even though each particle pair cannot bind. Interestingly, the properties of these aggregates, such as the peculiar geometric scaling of their energy spectrum, are universal, i.e. independent of the microscopic details of their components. Despite an extensive search in many different physical systems, including nuclei, atoms and molecules, Efimov spectra have long eluded observation. Here we report on the first discovery of two bound trimer states of potassium atoms very close to the Efimov scenario, which we reveal by studying three-particle collisions in an ultracold gas with tunable interaction. Our observation provides the first evidence of an Efimov spectrum and allows a direct test of its scaling behavior, shedding new light onto the physics of few-body universal systems.

Research paper thumbnail of Erratum: Feshbach spectroscopy of a K-Rb atomic mixture

Physical Review A, 2006

We wish to correct a small error in the calibration of the magnetic field in the experiment repor... more We wish to correct a small error in the calibration of the magnetic field in the experiment reported in our paper. The correct value of the magnetic field positions of 40K-87Rb Feshbach resonances are reported in Table I. A newly found resonance in the ground ...

Research paper thumbnail of Feshbach spectroscopy of a K-Rb atomic mixture

Physical Review A, 2006

We perform extensive magnetic Feshbach spectroscopy of an ultracold mixture of fermionic 40K and ... more We perform extensive magnetic Feshbach spectroscopy of an ultracold mixture of fermionic 40K and bosonic 87Rb atoms. The magnetic-field locations of 14 interspecies resonances is used to construct a quantum collision model able to predict accurate collisional parameters for all K-Rb isotopic pairs. In particular we determine the interspecies s-wave singlet and triplet scattering lengths for the 40K-87Rb mixture as -111 +/- 5 Bohr and -215 +/- 10 Bohr respectively. We also predict accurate scattering lengths and position of Feshbach resonances for the other K-Rb isotopic pairs. We discuss the consequences of our results for current and future experiments with ultracold K-Rb mixtures.

Research paper thumbnail of Effects of interactions on an Anderson insulator in a disordered lattice

Anderson localization of ultracold atoms in disordered optical lattices, i.e. the transition from... more Anderson localization of ultracold atoms in disordered optical lattices, i.e. the transition from extended to exponentially localized states, was recently demonstrated for non-interacting samples. With the addition of atomic interactions, the system becomes more complicated and more difficult to describe theoretically. The effects of the disorder are expected to be gradually suppressed, and the possibility of different quantum phases arises. In our system, we employ a ^39K Bose gas, where the interaction can be tuned from negligible to large values via a Feshbach resonance. We employ a one-dimensional incommensurate bichromatic optical lattice as a model of a controllable disordered system. In this talk, we present recent experimental results showing a transition from the Anderson-insulator phase to a superfluid phase.

Research paper thumbnail of Atom Interferometry with a Weakly Interacting Bose-Einstein Condensate

Physical Review Letters, 2008

Bose-Einstein condensates have been considered since long the most appropriate source for interfe... more Bose-Einstein condensates have been considered since long the most appropriate source for interferometry with matter waves, due to their maximal coherence properties. However, the realization of practical interferometers with condensates has been so far hindered by the presence of the natural atom-atom interaction, which dramatically affects their performance. We will report on the realization of an interferometer based on a Bose-Einstein condensate of 39 K atoms, where the contact interaction between atoms can be tuned by means of a Feshbach resonance 1 . We observe that the coherence time of the interferometer is greatly enhanced by a reduction of the contact interaction by orders of magnitude from the standard value 2 . We also study the effect of the residual magnetic dipole-dipole interaction.

Research paper thumbnail of Magnetic Dipolar Interaction in a Bose-Einstein Condensate Atomic Interferometer

Physical Review Letters, 2008

We study the role played by the magnetic dipole interaction in an atomic interferometer based on ... more We study the role played by the magnetic dipole interaction in an atomic interferometer based on an alkali Bose-Einstein condensate with tunable scattering length. We tune the s-wave interaction to zero using a magnetic Feshbach resonance and measure the decoherence of the interferometer induced by the weak residual interaction between the magnetic dipoles of the atoms. We prove that with a proper choice of the scattering length it is possible to compensate for the dipolar interaction and extend the coherence time of the interferometer. We put in evidence the anisotropic character of the dipolar interaction by working with two different experimental configurations for which the minima of decoherence are achieved for a positive and a negative value of the scattering length, respectively. Our results are supported by a theoretical model we develop. This model indicates that the magnetic dipole interaction should not represent a serious source of decoherence in atom interferometers based on Bose-Einstein condensates.

Research paper thumbnail of K39 Bose-Einstein Condensate with Tunable Interactions

Physical Review Letters, 2007

We produce a Bose-Einstein condensate of 39-K atoms. Condensation of this species with naturally ... more We produce a Bose-Einstein condensate of 39-K atoms. Condensation of this species with naturally small and negative scattering length is achieved by a combination of sympathetic cooling with 87-Rb and direct evaporation, exploiting the magnetic tuning of both inter- and intra-species interactions at Feshbach resonances. We explore tunability of the self-interactions by studying the expansion and the stability of the condensate. We find that a 39-K condensate is interesting for future experiments requiring a weakly interacting Bose gas.

Research paper thumbnail of Anderson localization of a non-interacting Bose-Einstein condensate

Nature, 2008

One of the most intriguing phenomena in physics is the localization of waves in disordered media.... more One of the most intriguing phenomena in physics is the localization of waves in disordered media. This phenomenon was originally predicted by Anderson, fifty years ago, in the context of transport of electrons in crystals. Anderson localization is actually a much more general phenomenon, and it has been observed in a large variety of systems, including light waves. However, it has never been observed directly for matter waves. Ultracold atoms open a new scenario for the study of disorder-induced localization, due to high degree of control of most of the system parameters, including interaction. Here we employ for the first time a noninteracting Bose-Einstein condensate to study Anderson localization. The experiment is performed with a onedimensional quasi-periodic lattice, a system which features a crossover between extended and exponentially localized states as in the case of purely random disorder in higher dimensions. Localization is clearly demonstrated by investigating transport properties, spatial and momentum distributions. We characterize the crossover, finding that the critical disorder strength scales with the tunnelling energy of the atoms in the lattice. Since the interaction in the condensate can be controlled at will, this system might be employed to solve open questions on the interplay of disorder and interaction and to explore exotic quantum phases.

Research paper thumbnail of Anderson Localization of a Non-Interacting Bose-Einstein Condensate

One of the most intriguing phenomena in physics is the localization of waves in disordered media.... more One of the most intriguing phenomena in physics is the localization of waves in disordered media. This phenomenon was originally predicted by P. W. Anderson, fifty years ago, in the context of transport of electrons in crystals, but it has never been directly observed for matter waves. Ultracold atoms open a new scenario for the study of disorder-induced localization, due to the high degree of control of most of the system parameters, including interactions. For the first time we have employed a noninteracting Bose-Einstein condensate to study Anderson localization. The experiment is performed in a 1D lattice with quasi-periodic disorder, a system which features a crossover between extended and exponentially localized states as in the case of purely random disorder in higher dimensions. We clearly demonstrate localization by investigating transport properties, spatial and momentum distributions. Since the interaction in the condensate can be controlled, this system represents a novel tool to solve fundamental questions on the interplay of disorder and interactions and to explore exotic quantum phases.

Research paper thumbnail of Feshbach resonances in ultracold 39K

New Journal of Physics, 2007

We discover several magnetic Feshbach resonances in collisions of ultracold K(39) atoms, by study... more We discover several magnetic Feshbach resonances in collisions of ultracold K(39) atoms, by studying atom losses and molecule formation. Accurate determination of the magnetic-field resonance locations allows us to optimize a quantum collision model for potassium isotopes. We employ the model to predict the magnetic-field dependence of scattering lengths and of near-threshold molecular levels. Our findings will be useful to plan future experiments on ultracold potassium atoms and molecules.

Research paper thumbnail of Observation of an Efimov spectrum in an atomic system

Nature Physics, 2009

In 1970 V. Efimov predicted a puzzling quantum-mechanical effect that is still of great interest ... more In 1970 V. Efimov predicted a puzzling quantum-mechanical effect that is still of great interest today. He found that three particles subjected to a resonant pairwise interaction can join into an infinite number of loosely bound states even though each particle pair cannot bind. Interestingly, the properties of these aggregates, such as the peculiar geometric scaling of their energy spectrum, are universal, i.e. independent of the microscopic details of their components. Despite an extensive search in many different physical systems, including atoms, molecules and nuclei, the characteristic spectrum of Efimov trimer states still eludes observation. Here we report on the discovery of two bound trimer states of potassium atoms very close to the Efimov scenario, which we reveal by studying three-particle collisions in an ultracold gas. Our observation provides the first evidence of an Efimov spectrum and allows a direct test of its scaling behaviour, shedding new light onto the physics of few-body systems.

Research paper thumbnail of Delocalization of a disordered bosonic system by repulsive interactions

Nature Physics, 2010

Clarifying the interplay of interactions and disorder is fundamental to the understanding of many... more Clarifying the interplay of interactions and disorder is fundamental to the understanding of many quantum systems, including superfluid helium in porous media, granular and thin-film superconductors, and light propagating in disordered media. One central aspect for bosonic systems is the competition between disorder, which tends to localize particles, and weak repulsive interactions, which instead have a delocalizing effect. Since the required degree of independent control of the disorder and of the interactions is not easily achievable in most available physical systems, a systematic experimental investigation of this competition has so far not been possible. Here we employ an ultracold atomic Bose-Einstein condensate with tunable repulsive interactions in a quasi-periodic lattice potential to study this interplay in detail. We characterize the entire delocalization crossover through the study of the average local shape of the wavefunction, the spatial correlations, and the phase coherence. Three different regimes are identified and compared with theoretical expectations: an exponentially localized Anderson glass, the formation of locally coherent fragments, as well as a coherent, extended state. Our results illuminate the role of weak repulsive interactions on disordered bosonic systems and show that the system and the techniques we employ are promising for further investigations of disordered systems with interactions, also in the strongly correlated regime.

Research paper thumbnail of Control of the interaction in a Fermi-Bose mixture

Physical Review A, 2006

We control the interspecies interaction in a two-species atomic quantum mixture by tuning the mag... more We control the interspecies interaction in a two-species atomic quantum mixture by tuning the magnetic field at a Feshbach resonance. The mixture is composed by fermionic 40K and bosonic 87Rb. We observe effects of the large attractive and repulsive interaction energy across the resonance, such as collapse or a reduced spatial overlap of the mixture, and we accurately locate the resonance position and width. Understanding and controlling instabilities in this mixture opens the way to a variety of applications, including formation of heteronuclear molecular quantum gases.

Research paper thumbnail of Near-threshold model for ultracold KRb dimers from interisotope Feshbach spectroscopy

Physical Review A, 2008

We investigate magnetic Feshbach resonances in two different ultracold K-Rb mixtures. Information... more We investigate magnetic Feshbach resonances in two different ultracold K-Rb mixtures. Information on the K(39)-Rb(87) isotopic pair is combined with novel and pre-existing observations of resonance patterns for K(40)-Rb(87). Interisotope resonance spectroscopy improves significantly our near-threshold model for scattering and bound-state calculations. Our analysis determines the number of bound states in singlet/triplet potentials and establishes precisely near threshold parameters for all K-Rb pairs of interest for experiments with both atoms and molecules. In addition, the model verifies the validity of the Born-Oppenheimer approximation at the present level of accuracy.

Research paper thumbnail of Atom Interferometry with a Weakly Interacting Bose-Einstein Condensate

Bose-Einstein condensates have long been considered the most appropriate source for interferometr... more Bose-Einstein condensates have long been considered the most appropriate source for interferometry with matter waves, due to their maximal coherence properties. However, the realization of practical interferometers with condensates has been so far hindered by the presence of the natural atom-atom interaction, which dramatically affects their performance. We describe here the realization of a lattice-based interferometer based on a Bose-Einstein condensate where the contact interaction can be tuned by means of a Feshbach resonance, and eventually reduced towards zero. We observe a strong increase of the coherence time of the interferometer with vanishing scattering length, and see evidence of the effect of the weak magnetic dipole-dipole interaction. Our observations indicate that high-sensitivity atom interferometry with Bose-Einstein condensates is feasible, via a precise control of the interactions.

Research paper thumbnail of Magnetic dipolar interaction in an atomic Bose Einstein condensate interferometer

Physical Review Letters, 2008

We study the role played by the magnetic dipole interaction in an atomic interferometer based on ... more We study the role played by the magnetic dipole interaction in an atomic interferometer based on an alkali Bose-Einstein condensate with tunable scattering length. We tune the s-wave interaction to zero using a magnetic Feshbach resonance and measure the decoherence of the interferometer induced by the weak residual interaction between the magnetic dipoles of the atoms. We prove that with a proper choice of the scattering length it is possible to compensate for the dipolar interaction and extend the coherence time of the interferometer. We put in evidence the anisotropic character of the dipolar interaction by working with two different experimental configurations for which the minima of decoherence are achieved for a positive and a negative value of the scattering length, respectively. Our results are supported by a theoretical model we develop. This model indicates that the magnetic dipole interaction should not represent a serious source of decoherence in atom interferometers based on Bose-Einstein condensates.

Research paper thumbnail of Observation of an Efimov spectrum in an atomic system

In 1970 the Russian physicist V. Efimov predicted a puzzling quantum mechanical effect that is st... more In 1970 the Russian physicist V. Efimov predicted a puzzling quantum mechanical effect that is still of great interest today. He found that three particles subjected to a resonant pairwise interaction can join into an infinite number of loosely bound states even though each particle pair cannot bind. Interestingly, the properties of these aggregates, such as the peculiar geometric scaling of their energy spectrum, are universal, i.e. independent of the microscopic details of their components. Despite an extensive search in many different physical systems, including nuclei, atoms and molecules, Efimov spectra have long eluded observation. Here we report on the first discovery of two bound trimer states of potassium atoms very close to the Efimov scenario, which we reveal by studying three-particle collisions in an ultracold gas with tunable interaction. Our observation provides the first evidence of an Efimov spectrum and allows a direct test of its scaling behavior, shedding new light onto the physics of few-body universal systems.

Research paper thumbnail of Erratum: Feshbach spectroscopy of a K-Rb atomic mixture

Physical Review A, 2006

We wish to correct a small error in the calibration of the magnetic field in the experiment repor... more We wish to correct a small error in the calibration of the magnetic field in the experiment reported in our paper. The correct value of the magnetic field positions of 40K-87Rb Feshbach resonances are reported in Table I. A newly found resonance in the ground ...

Research paper thumbnail of Feshbach spectroscopy of a K-Rb atomic mixture

Physical Review A, 2006

We perform extensive magnetic Feshbach spectroscopy of an ultracold mixture of fermionic 40K and ... more We perform extensive magnetic Feshbach spectroscopy of an ultracold mixture of fermionic 40K and bosonic 87Rb atoms. The magnetic-field locations of 14 interspecies resonances is used to construct a quantum collision model able to predict accurate collisional parameters for all K-Rb isotopic pairs. In particular we determine the interspecies s-wave singlet and triplet scattering lengths for the 40K-87Rb mixture as -111 +/- 5 Bohr and -215 +/- 10 Bohr respectively. We also predict accurate scattering lengths and position of Feshbach resonances for the other K-Rb isotopic pairs. We discuss the consequences of our results for current and future experiments with ultracold K-Rb mixtures.

Research paper thumbnail of Effects of interactions on an Anderson insulator in a disordered lattice

Anderson localization of ultracold atoms in disordered optical lattices, i.e. the transition from... more Anderson localization of ultracold atoms in disordered optical lattices, i.e. the transition from extended to exponentially localized states, was recently demonstrated for non-interacting samples. With the addition of atomic interactions, the system becomes more complicated and more difficult to describe theoretically. The effects of the disorder are expected to be gradually suppressed, and the possibility of different quantum phases arises. In our system, we employ a ^39K Bose gas, where the interaction can be tuned from negligible to large values via a Feshbach resonance. We employ a one-dimensional incommensurate bichromatic optical lattice as a model of a controllable disordered system. In this talk, we present recent experimental results showing a transition from the Anderson-insulator phase to a superfluid phase.

Research paper thumbnail of Atom Interferometry with a Weakly Interacting Bose-Einstein Condensate

Physical Review Letters, 2008

Bose-Einstein condensates have been considered since long the most appropriate source for interfe... more Bose-Einstein condensates have been considered since long the most appropriate source for interferometry with matter waves, due to their maximal coherence properties. However, the realization of practical interferometers with condensates has been so far hindered by the presence of the natural atom-atom interaction, which dramatically affects their performance. We will report on the realization of an interferometer based on a Bose-Einstein condensate of 39 K atoms, where the contact interaction between atoms can be tuned by means of a Feshbach resonance 1 . We observe that the coherence time of the interferometer is greatly enhanced by a reduction of the contact interaction by orders of magnitude from the standard value 2 . We also study the effect of the residual magnetic dipole-dipole interaction.

Research paper thumbnail of Magnetic Dipolar Interaction in a Bose-Einstein Condensate Atomic Interferometer

Physical Review Letters, 2008

We study the role played by the magnetic dipole interaction in an atomic interferometer based on ... more We study the role played by the magnetic dipole interaction in an atomic interferometer based on an alkali Bose-Einstein condensate with tunable scattering length. We tune the s-wave interaction to zero using a magnetic Feshbach resonance and measure the decoherence of the interferometer induced by the weak residual interaction between the magnetic dipoles of the atoms. We prove that with a proper choice of the scattering length it is possible to compensate for the dipolar interaction and extend the coherence time of the interferometer. We put in evidence the anisotropic character of the dipolar interaction by working with two different experimental configurations for which the minima of decoherence are achieved for a positive and a negative value of the scattering length, respectively. Our results are supported by a theoretical model we develop. This model indicates that the magnetic dipole interaction should not represent a serious source of decoherence in atom interferometers based on Bose-Einstein condensates.

Research paper thumbnail of K39 Bose-Einstein Condensate with Tunable Interactions

Physical Review Letters, 2007

We produce a Bose-Einstein condensate of 39-K atoms. Condensation of this species with naturally ... more We produce a Bose-Einstein condensate of 39-K atoms. Condensation of this species with naturally small and negative scattering length is achieved by a combination of sympathetic cooling with 87-Rb and direct evaporation, exploiting the magnetic tuning of both inter- and intra-species interactions at Feshbach resonances. We explore tunability of the self-interactions by studying the expansion and the stability of the condensate. We find that a 39-K condensate is interesting for future experiments requiring a weakly interacting Bose gas.

Research paper thumbnail of Anderson localization of a non-interacting Bose-Einstein condensate

Nature, 2008

One of the most intriguing phenomena in physics is the localization of waves in disordered media.... more One of the most intriguing phenomena in physics is the localization of waves in disordered media. This phenomenon was originally predicted by Anderson, fifty years ago, in the context of transport of electrons in crystals. Anderson localization is actually a much more general phenomenon, and it has been observed in a large variety of systems, including light waves. However, it has never been observed directly for matter waves. Ultracold atoms open a new scenario for the study of disorder-induced localization, due to high degree of control of most of the system parameters, including interaction. Here we employ for the first time a noninteracting Bose-Einstein condensate to study Anderson localization. The experiment is performed with a onedimensional quasi-periodic lattice, a system which features a crossover between extended and exponentially localized states as in the case of purely random disorder in higher dimensions. Localization is clearly demonstrated by investigating transport properties, spatial and momentum distributions. We characterize the crossover, finding that the critical disorder strength scales with the tunnelling energy of the atoms in the lattice. Since the interaction in the condensate can be controlled at will, this system might be employed to solve open questions on the interplay of disorder and interaction and to explore exotic quantum phases.

Research paper thumbnail of Anderson Localization of a Non-Interacting Bose-Einstein Condensate

One of the most intriguing phenomena in physics is the localization of waves in disordered media.... more One of the most intriguing phenomena in physics is the localization of waves in disordered media. This phenomenon was originally predicted by P. W. Anderson, fifty years ago, in the context of transport of electrons in crystals, but it has never been directly observed for matter waves. Ultracold atoms open a new scenario for the study of disorder-induced localization, due to the high degree of control of most of the system parameters, including interactions. For the first time we have employed a noninteracting Bose-Einstein condensate to study Anderson localization. The experiment is performed in a 1D lattice with quasi-periodic disorder, a system which features a crossover between extended and exponentially localized states as in the case of purely random disorder in higher dimensions. We clearly demonstrate localization by investigating transport properties, spatial and momentum distributions. Since the interaction in the condensate can be controlled, this system represents a novel tool to solve fundamental questions on the interplay of disorder and interactions and to explore exotic quantum phases.

Research paper thumbnail of Feshbach resonances in ultracold 39K

New Journal of Physics, 2007

We discover several magnetic Feshbach resonances in collisions of ultracold K(39) atoms, by study... more We discover several magnetic Feshbach resonances in collisions of ultracold K(39) atoms, by studying atom losses and molecule formation. Accurate determination of the magnetic-field resonance locations allows us to optimize a quantum collision model for potassium isotopes. We employ the model to predict the magnetic-field dependence of scattering lengths and of near-threshold molecular levels. Our findings will be useful to plan future experiments on ultracold potassium atoms and molecules.

Research paper thumbnail of Observation of an Efimov spectrum in an atomic system

Nature Physics, 2009

In 1970 V. Efimov predicted a puzzling quantum-mechanical effect that is still of great interest ... more In 1970 V. Efimov predicted a puzzling quantum-mechanical effect that is still of great interest today. He found that three particles subjected to a resonant pairwise interaction can join into an infinite number of loosely bound states even though each particle pair cannot bind. Interestingly, the properties of these aggregates, such as the peculiar geometric scaling of their energy spectrum, are universal, i.e. independent of the microscopic details of their components. Despite an extensive search in many different physical systems, including atoms, molecules and nuclei, the characteristic spectrum of Efimov trimer states still eludes observation. Here we report on the discovery of two bound trimer states of potassium atoms very close to the Efimov scenario, which we reveal by studying three-particle collisions in an ultracold gas. Our observation provides the first evidence of an Efimov spectrum and allows a direct test of its scaling behaviour, shedding new light onto the physics of few-body systems.

Research paper thumbnail of Delocalization of a disordered bosonic system by repulsive interactions

Nature Physics, 2010

Clarifying the interplay of interactions and disorder is fundamental to the understanding of many... more Clarifying the interplay of interactions and disorder is fundamental to the understanding of many quantum systems, including superfluid helium in porous media, granular and thin-film superconductors, and light propagating in disordered media. One central aspect for bosonic systems is the competition between disorder, which tends to localize particles, and weak repulsive interactions, which instead have a delocalizing effect. Since the required degree of independent control of the disorder and of the interactions is not easily achievable in most available physical systems, a systematic experimental investigation of this competition has so far not been possible. Here we employ an ultracold atomic Bose-Einstein condensate with tunable repulsive interactions in a quasi-periodic lattice potential to study this interplay in detail. We characterize the entire delocalization crossover through the study of the average local shape of the wavefunction, the spatial correlations, and the phase coherence. Three different regimes are identified and compared with theoretical expectations: an exponentially localized Anderson glass, the formation of locally coherent fragments, as well as a coherent, extended state. Our results illuminate the role of weak repulsive interactions on disordered bosonic systems and show that the system and the techniques we employ are promising for further investigations of disordered systems with interactions, also in the strongly correlated regime.

Research paper thumbnail of Control of the interaction in a Fermi-Bose mixture

Physical Review A, 2006

We control the interspecies interaction in a two-species atomic quantum mixture by tuning the mag... more We control the interspecies interaction in a two-species atomic quantum mixture by tuning the magnetic field at a Feshbach resonance. The mixture is composed by fermionic 40K and bosonic 87Rb. We observe effects of the large attractive and repulsive interaction energy across the resonance, such as collapse or a reduced spatial overlap of the mixture, and we accurately locate the resonance position and width. Understanding and controlling instabilities in this mixture opens the way to a variety of applications, including formation of heteronuclear molecular quantum gases.

Research paper thumbnail of Near-threshold model for ultracold KRb dimers from interisotope Feshbach spectroscopy

Physical Review A, 2008

We investigate magnetic Feshbach resonances in two different ultracold K-Rb mixtures. Information... more We investigate magnetic Feshbach resonances in two different ultracold K-Rb mixtures. Information on the K(39)-Rb(87) isotopic pair is combined with novel and pre-existing observations of resonance patterns for K(40)-Rb(87). Interisotope resonance spectroscopy improves significantly our near-threshold model for scattering and bound-state calculations. Our analysis determines the number of bound states in singlet/triplet potentials and establishes precisely near threshold parameters for all K-Rb pairs of interest for experiments with both atoms and molecules. In addition, the model verifies the validity of the Born-Oppenheimer approximation at the present level of accuracy.