We study the horizontal expansion of vertically confined ultra-cold atoms in the presence of disorder. Vertical confinement allows us to realize a situation with a few coupled harmonic oscillator quantum states. The disordered potential is created by an optical speckle at an angle of 30◦ with respect to the horizontal plane, resulting in an effective anisotropy of the correlation lengths of a factor of 2 in that plane. We observe diffusion leading to non-Gaussian density profiles. Diffusion coefficients, extracted from the experimental results, show anisotropy and strong energy dependence, in agreement with numerical calculations.

We report the possibility to simultaneously perform wide-field nitrogen-vacancy (NV) diamond magnetic microscopy and synchrotron x-ray diffraction measurements at high pressure. NV color centers are created on the culet of a diamond anvil which is integrated in a diamond anvil cell for static compression of the sample. The optically detected spin resonance of the NV centers is used to map the stray magnetic field produced by the sample magnetization. Using this combined scheme, the magnetic and structural behaviors can be simultaneously measured. As a proof-of-principle, we record the correlated alpha-Fe to epsilon-Fe structural and magnetic transitions of iron that occur here between 15 and 20 GPa at 300 K.

The phase diagram and melting curve of water ice is investigated up to 45 GPa and 1600 K by synchrotron x-ray diffraction in the resistively and laser heated diamond anvil cell. Our melting data evidence a triple point at 14.6 GPa, 850 K. The latter is shown to be related to a first-order solid transition from the dynamically disordered form of ice VII, denoted ice VII^{'}, toward a high-temperature phase with the same bcc oxygen lattice but larger volume and higher entropy. Our experiments are compared to ab initio molecular dynamics simulations, enabling us to identify the high-temperature bcc phase with the predicted superionic ice VII^{''} phase [J.-A. Hernandez and R. Caracas, Phys. Rev. Lett. 117, 135503 (2016).PRLTAO0031-900710.1103/PhysRevLett.117.135503].

The melting curve and stability of ammonia (NH3) is investigated up to 40 GPa and 3500 K by x-ray diffraction and Raman spectroscopy in the laser-heated diamond anvil cell. The NH3 samples were directly heated by the 10.6 mu m radiation of a CO2 laser to reduce the risks of chemical reactions. Melting was unambiguously detected by the appearance of the liquid diffraction signal upon temperature increase. The melting temperature of NH3 is found to steadily increase with pressure up to 40 GPa, and the previously reported turnover is not observed. As a result, the melting line of NH3 is expected to cross the isentropes of Neptune and Uranus in the pressure range 55-65 GPa, implying the possible presence of superionic solid NH3 in these planets. Our x-ray and Raman measurements confirm the appearance of N-2 and H-2 upon heating the liquid phase from 6 to 40 GPa. But while the equilibrium 2NH(3) reversible arrow N-2 + 3H(2) balances towards the dissociated elements at low pressure and high temperature, ammonia is found to the more stable species in the range 20-40 GPa, 300-3000 K.

Pressure can be used to tune the interplay among structural, electronic, and magnetic interactions in materials. High pressures are usually applied in the diamond anvil cell, making it difficult to study the magnetic properties of a micrometer-sized sample. We report a method for spatially resolved optical magnetometry based on imaging a layer of nitrogen-vacancy (NV) centers created at the surface of a diamond anvil. We illustrate the method using two sets of measurements realized at room temperature and low temperature, respectively: the pressure evolution of the magnetization of an iron bead up to 30 gigapascals showing the iron ferromagnetic collapse and the detection of the superconducting transition of magnesium dibromide at 7 gigapascals.

Data description.pdf describes the uploaded data. Figure Data.xlsx contains the data represented in the figures of the main text and supplementary information. Iron.zip and MgB2.zip include the raw experimental data. PlotIronData.m, PlotMgB2Data.m, SimulatedIronMagneticField.m, SphereField.m, CarttoPol.m, PoltoCart.m are Matlab codes used to process and fit the data.

Synchrotron x-ray diffraction measurements of nitrogen are performed up to 120 GPa to determine the melting curve and the structural changes of the solid and liquid phases along it. The melting temperature exhibits a monotonic increase up to the triple point where the epsilon molecular solid, the cubic gauche covalent solid, and the fluid meet at 116 GPa, 2080 K. Above, the stability of the cubic gauche phase induces a sharp increase of the melting curve. The structural data on liquid nitrogen show that the latter remains molecular over the whole probed domain, which contradicts the prediction of a liquid-liquid transition at 88 GPa, 2000 K. These findings thus largely revisit the phase diagram of hot dense nitrogen and challenge the current understanding of this model system.

The equation of state and the unit cell parameters of triamino-trinitrobenzene (TATB) have been measured up to 66 GPa by x-ray diffraction on multi-grain samples. A custom indexing of the diffraction pattern was implemented to enable an unambiguous assignment of the diffraction peaks. The structural data reveal a more isotropic response to compression above 10 GPa, indicating that the van der Waals forces are no more the dominant interplanar interactions. The unit cell parameters are compared with density functional theory calculations, including the empirical D2 correction for the van der Waals interactions. An excellent agreement is obtained up to 20 GPa and an increasing deviation above. The present determination of the TATB isothermal equation of state is reliable for detonation physics applications.

We present an experimental determination of the ambient temperature equation of state, P(ρ/ρ0,293 K), up to 45 GPa, of the glow discharge polymer (GDP) used as a confining capsule for the fusible deuterium-tritium mixture in inertial confinement fusion experiments. An original method has been implemented to measure both the compression factor and the refractive index versus pressure. The data are obtained in a diamond anvil cell with two sample chambers of equal thickness containing, respectively, the GDP and a NaCl reference. This experimental equation of state is compared to numerical first principles simulations. Deviations are ascribed to the difficulty to simulate the detailed atomic structure of the polymer under moderate pressure.

Glow discharge polymer hydrocarbon (GDP-CH) is used as the ablator material in inertial confinement fusion (ICF) capsules for the Laser Mégajoule and National Ignition Facility. Due to its fabrication process, GDP-CH chemical composition and structure differ from commercially available plastics and detailed knowledge of its properties in the warm dense matter regime is needed to achieve accurate design of ICF capsules. First-principles ab initio simulations of the GDP-CH principal Hugoniot up to 8 Mbar were performed using the quantum molecular dynamics (QMD) code abinit and showed that atomic bond dissociation has an effect on the compressibility. Results from these simulations are used to parametrize a quantum semiempirical model in order to generate a tabulated equation of state that includes dissociation. Hugoniot measurements obtained from an experiment conducted at the LULI2000 laser facility confirm QMD simulations as well as EOS modeling. We conclude by showing the EOS model influence on shock timing in a hydrodynamic simulation.

The center-of-mass structure factor, S(Q), of liquid hydrogen and liquid deuterium has been measured up to 5 GPa, mostly along the melting line from 50 to 296 K. Good quality data were achieved thanks to a novel synchrotron x-ray technique that can isolate the very weak x-ray scattering signal of the micrometric volume of hydrogen compressed in the diamond anvil cell. S(Q) is dominated by a broad peak and hence, its wave-vector position, Q(m), is used to appreciate the structural changes in the system. An isotope effect in the position of Q(m) is observed that can be explained by a density effect. The shift of Q(m) towards higher Q as density increases is followed over a threefold compression. Two simple liquid type evolutions are disclosed with a crossover between them around 37 nm(-3)/molecule. An interpretation is proposed based on the change in the zero-point motional renormalization of the interaction from anharmonic to harmonic.

The binary phase diagram of N-2-Ne mixtures has been measured at 296 K by visual observation and Raman spectroscopy. The topology of the phase diagram points to the existence of the stoichiometric compound (N-2)(6)Ne-7. Its structure has been solved by single-crystal synchrotron x-ray diffraction. The N-2 molecules form a guest lattice that hosts the Ne atoms. This insertion compound can be viewed as a clathrate with the centers of the N-2 molecules forming distorted dodecahedron cages, each enclosing 14 Ne atoms. Remarkably, the (N-2)(6)Ne-7 compound is somehow the first clathrate organized by the quadrupolar interaction.

When particles are multiply scattered by a random potential, their momentum distribution becomes isotropic on average. We study this quantum dynamics numerically and with a master equation. We show how to measure the elastic scattering time as well as characteristic isotropisation times, which permit to reconstruct the scattering phase function, even in rather strong disorder.

We report on the direct observation of coherent backscattering (CBS) of ultracold atoms in a quasi-two-dimensional configuration. Launching atoms with a well-defined momentum in a laser speckle disordered potential, we follow the progressive build up of the momentum scattering pattern, consisting of a ring associated with multiple elastic scattering, and the CBS peak in the backward direction. Monitoring the depletion of the initial momentum component and the formation of the angular ring profile allows us to determine microscopic transport quantities. We also study the time evolution of the CBS peak and find it in fair agreement with predictions, at long times as well as at short times. The observation of CBS can be considered a direct signature of coherence in quantum transport of particles in disordered media. It is responsible for the so called weak localization phenomenon, which is the precursor of Anderson localization.

Hanbury Brown and Twiss (HBT) correlations, i.e. correlations in far-field intensity fluctuations, yield fundamental information on the quantum statistics of light sources, as highlighted after the discovery of photon bunching. Drawing on the analogy between photons and atoms, similar measurements have been performed for matter-wave sources, probing density fluctuations of expanding ultracold Bose gases. Here we use two-point density correlations to study how coherence is gradually established when crossing the Bose-Einstein condensation (BEC) threshold. Our experiments reveal a persistent multimode character of the emerging matter-wave as seen in the non-trivial spatial shape of the correlation functions for all probed source geometries from nearly isotropic to quasi-one-dimensional (quasi-1D), and for all probed temperatures. The qualitative features of our observations are captured by ideal Bose gas theory, the quantitative differences illustrate the role of particle interactions.

We experimentally study the effect of disorder on trapped quasi two-dimensional (2D) 87Rb clouds in the vicinity of the Berezinskii-Kosterlitz-Thouless (BKT) phase transition. The disorder correlation length is of the order of the Bose gas characteristic length scales (thermal de Broglie wavelength, healing length) and disorder thus modifies the physics at a microscopic level. We analyze the coherence properties of the cloud through measurements of the momentum distributions, for two disorder strengths, as a function of its degeneracy. For moderate disorder, the emergence of coherence remains steep but is shifted to a lower entropy. In contrast, for strong disorder, the growth of coherence is hindered. Our study is an experimental realization of the dirty boson problem in a well controlled atomic system suitable for quantitative analysis.