We report on the observation of controllable phase separation in a dual-species Bose-Einstein condensate with 85 Rb and 87 Rb. Interatomic interactions between the different components determine the miscibility of the two quantum fluids. In our experiments, we can clearly observe immiscible behavior via a dramatic spatial separation of the two species. Furthermore, a magnetic-field Feshbach resonance is used to change them between miscible and immiscible by tuning the 85 Rb scattering length. The spatial density pattern of the immiscible quantum fluids exhibits complex alternating-domain structures that are uncharacteristic of its stationary ground state. . Ultracold quantum gases also provide a unique opportunity to study the miscibility of interpenetrating quantum fluids. They exhibit numerous advantages including the resonant control of two-body interactions via magnetic-field Feshbach resonances, which provides a parameter to directly alter the miscibility of the fluids.The first two-component condensate was produced with different hyperfine states of 87 Rb, and evidence for repulsive interactions between the two clouds was reported [2]. The dynamical behavior of a two-component BoseEinstein condensate (BEC) has been studied extensively [3,4] including the dramatic observation of weakly damped collective oscillations [5]. In spinor condensates both miscible and immiscible two-component condensates were observed for the first time [6]. They formed long-lived metastable excited states composed of magnetic domains [7], and tunneling effects between the domains were studied [8]. Dual-species quantum gases are currently a subject of significant interest. In particular, an outstanding goal is the creation of ultracold heteronuclear molecules in low-lying vibrational states. Such molecules are expected to possess a dipole moment that could be utilized for such varied applications as quantum information and the search for the electron electric dipole moment [9]. A dual-species BEC of 41 K and 87 Rb has already been realized in a harmonic potential [10] and in an optical lattice [11]. In a Bose-Fermi mixture of 40 K and 87 Rb, a tunable interspecies scattering length was used to probe both phase separation of the mixture and interaction-induced collapse [12].Understanding how the spatial overlap of a dual-species BEC changes as interactions are tuned will be important for future experiments. In this Letter, we explore the tunable miscibility of a Bose-condensed mixture of 85 Rb and 87 Rb gases. Immiscibility of the two-component quantum gas is observed as a dramatic departure of the density distribution from the symmetry of the trapping potential. Surprisingly, we observe the robust formation of multiple, nonoverlapped, single-species BEC ''cloudlets'' that represent an interesting presumably metastable excited state.Theoretical investigations of two-component condensates have illuminated the role that interatomic interactions play in determining the density patterns and phase separation of the components [13][14][15...

We report on measurements of the excitation spectrum of a strongly interacting Bose-Einstein condensate. A magnetic-field Feshbach resonance is used to tune atom-atom interactions in the condensate and to reach a regime where quantum depletion and beyond mean-field corrections to the condensate chemical potential are significant. We use two-photon Bragg spectroscopy to probe the condensate excitation spectrum; our results demonstrate the onset of beyond mean-field effects in a gaseous Bose-Einstein condensate.

A powerful set of universal relations, centered on a quantity called the contact, connects the strength of short-range two-body correlations to the thermodynamics of a many-body system with delta-function interactions. We report on measurements of the contact, using RF spectroscopy, for an 85 Rb atomic Bose-Einstein condensate (BEC). For bosons, the fact that contact spectroscopy can be used to probe the gas on short timescales is useful given the decreasing stability of BECs with increasing interactions. A complication is the added possibility, for bosons, of three-body interactions. In investigating this issue, we have located an Efimov resonance for 85 Rb atoms with loss measurements and thus determined the three-body interaction parameter. In our contact spectroscopy, in a region of observable beyond-mean-field effects, we find no measurable contribution from three-body physics.Systems with strong quantum correlations represent a frontier in our understanding of the complex quantum systems found in nature, and atomic Bose-Einstein condensates (BEC) provide a versatile system in which to explore beyond mean-field physics. Ultracold atoms experience two-body, short-range interactions that are well described theoretically by a delta-function pseudopotential characterized by an s-wave scattering length a. In the simplest BEC experiments the values of a and of the density n are such that interactions are too weak, compared to the kinetic energy cost of correlations, to take the gas out of the mean-field regime. The presence of a lattice potential can greatly suppress this kinetic energy cost, thus freeing the system to explore a much richer portion of many-body state space [1]. The application of an external lattice potential, however, imposes an artificial orderliness not found in bosons in the wild. To explore strong interactions in a more naturalistic bulk three-dimensional gas, one can increase a by means of a magnetic-field-tunable Feshbach scattering resonance [2]. Such efforts are motivated for instance by a desire to make better conceptual connections to the iconic strongly correlated fluid, liquid helium.In practice it has proven difficult to study atomic BEC with increasing a and only a few experiments have measured beyond-mean-field interaction effects in these systems [3][4][5]. The difficulty comes from the fact that an increase in a is accompanied by a dramatic increase in the rate of inelastic three-body processes [6,7]. This leads to large losses and significant heating of the trapped gas on a timescale similar to that for global equilibrium of the trapped cloud. Probes of the gas that require global equilibrium, such as measurements of the density distribution or the amplitude or frequency of collective density oscillations in a trap, are therefore limited to systems that are only modestly out of the mean-field regime. Our strategy for exploring BEC with larger interaction strengths is to start from an equilibrated weakly interacting gas, change the interaction strength relatively quickly, forsa...

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We demonstrate a photon-counting technique for detecting Bragg excitation of an ultracold gas of atoms. By measuring the response of the light field to the atoms, we derive a signal independent of traditional time-of-flight atom-imaging techniques. With heterodyne detection we achieve photon shot-noise limited detection of the amplification or depletion of one of the Bragg laser beams. Photon counting for Bragg spectroscopy will be useful for strongly interacting gases where atom-imaging detection fails. In addition, this technique provides the ability to resolve the evolution of excitations as a function of pulse duration.

This study aims to determine if there is variation in precipitation concentrations in Chile. We analyzed daily and monthly records from 89 pluviometric stations in the period and distributed between 29 • 12 S and 39 • 30 S. This area was divided into two climatic zones: arid-semiarid and humid-subhumid. For each station, the Gini coefficient or Gini Index (GI), the precipitation concentration index (PCI), and the maximum annual precipitation intensity in a 24-h duration were calculated. These series of annual values were analyzed with the Mann-Kendall test with 5% error. Overall, it was noted that positive trends in the GI are present in both areas, although most were not found to be significant. In the case of PCI, the presence of positive trends is only present in the arid-semiarid zone; in the humid-subhumid zone, negative trends were mostly observed, although none of them were significant. Although no significant changes in all indices are evident, the particular case of the GI in the humid-subhumid zone stands out, where mostly positive trends were found (91.1%), of which 35.6% were significant. This would indicate that precipitation is more likely to be concentrated on a daily scale.

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