We study the coherent atomic tunneling between two zero-temperature BoseEinstein condensates (BEC) confined in a double-well magnetic trap. TwoGross-Pitaevskii equations for the self-interacting BEC amplitudes, coupled by a transfer matrix element, describe the dynamics in terms of the inter-well phase-difference and population imbalance. In addition to the anharmonic generalization of the familiar ac Josephson effect and plasma oscillations occurring in superconductor junctions, the non-linear BEC tunneling dynamics sustains a self-maintained population imbalance: a novel "macroscopic quantum self-trapping effect".

We discuss the coherent atomic oscillations between two weakly coupled Bose-Einstein condensates. The weak link is provided by a laser barrier in a (possibly asymmetric) double-well trap or by Raman coupling between two condensates in different hyperfine levels. The Boson Josephson Junction (BJJ) dynamics is described by the two-mode non-linear Gross-Pitaevskii equation, that is solved analytically in terms of elliptic functions. The BJJ, being a neutral, isolated system, allows the investigations of new dynamical regimes for the phase difference across the junction and for the population imbalance, that are not accessible with Superconductor Josephson Junctions (SJJ). These include oscillations with either, or both of the following properties: 1) the time-averaged value of the phase is equal to π (π − phase oscillations); 2) the average population imbalance is nonzero, in states with "macroscopic quantum self-trapping" (MQST). The (non-sinusoidal) gener-alization of the SJJ 'ac' and 'plasma' oscillations and the Shapiro resonance can also be observed. We predict the collapse of experimental data (corresponding to different trap geometries and total number of condensate atoms) onto a single universal curve, for the inverse period of oscillations.Analogies with Josephson oscillations between two weakly coupled reservoirs of 3 He-B and the internal Josephson effect in 3 He-A are also discussed.

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The cross section for inclusive electron scattering by nuclear matter is calculated at high momentum transfers using a microscopic spectral function, and compared with that extrapolated from data on laboratory nuclei. It is found that the cross section obtained with the plane-wave impulse approximation is close to the observed data at large values of the energy loss, but too small at low values. In this regime final-state interactions are important; after including their effects theory and data are in fair agreement.It is necessary to treat nucleon-nucleon correlations consistently in estimating the final-state interactions. The effects of possible time dependence of the nucleon-nucleon cross section, giving rise to nuclear transparency, are also investigated. The y scaling of the response function is discussed to further elucidate the role of final-state interactions. the response, due to the momentum distribution in the initial state, is proportional to~q~, as it is in the case of strongly interacting quantum liquids. If the width of the folding function is finite, then it can be argued that, at large enough values of~q~, FSI can be neglected, and, as a consequence, the response will exhibit y scaling. In con-2328 1991 The American Physical Society SCATTERING OF GeV ELECTRONS BY NUCLEAR MATTER 2329 trast, in the case of the nuclear medium at high q, one has to use relativistic kinematics and therefore the width of the response due to the momentum distribution of particles in the initial state is roughly constant -k~. It then follows that FSI eA'ects can be neglected only if the folding width goes to zero at large q. The folding width is of the order of the imaginary part of the optical potential which is -60 MeV -kF/4 for several hundreds MeV nucleons. Therefore, FSI are not obviously negligible in scattering of multi-GeV electrons by nuclei.Ideally, one should start from a realistic relativistically covariant theory of nuclei; however, such a theory is not yet practicable due to difFiculties in treating pionexchange interactions.In the plane-wave impulse ap-

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The Auxiliary Field Diffusion Monte Carlo method is applied to compute the spin susceptibility and the compressibility of neutron matter at zero temperature. Results are given for realistic interactions which include both a two-body potential of the Argonne type and the Urbana IX three-body potential. Simulations have been carried out for about 60 neutrons. We find an overall reduction of the spin susceptibilty by about a factor of 3 with respect to the Pauli susceptibility for a wide range of densities. Results for the compressibility of neutron matter are also presented and compared with other available estimates obtained for semirealistic nucleon-nucleon interactions and with more traditional many-body techniques, like Brueckner's or Correlated Basis Function theories.

We propose an experiment that would demonstrate the dc and ac Josephson effects in two weakly linked Bose-Einstein condensates. We consider a time-dependent barrier, moving adiabatically across the trapping potential. The phase dynamics are governed by a "driven-pendulum" equation, as in current-driven superconducting Josephson junctions. At a critical velocity of the barrier (proportional to the critical tunneling current), there is a sharp transition between the dc and ac regimes. The signature is a sudden jump of a large fraction of the relative condensate population. Analytical results are compared with a numerical integration of the Gross-Pitaevskii equation, in an experimentally realistic situation.