We describe the first direct measurement of the pair interaction potential for magnetic flux lines in a type-II superconductor. Our approach relies on a quantitative analysis of Lorentz microscope images of vortices creeping through a superconducting thin film. Time-resolved vortex distributions imaged in this way reflect both the vortices' mutual interaction and also the influence of random pinning forces. These influences are isolated and quantified by adapting results from the theory of simple liquids.

The D0 Collaboration has performed a measurement of the top quark mass $m_t$ based on six candidate events for the process $t\overline{t}\to {\mathrm{bW}}^{+}\overline{b}{W}^{-}$, where the $W$ bosons decay to $e\nu$ or $\mu \nu$. This sample was collected during an exposure of the D0 detector to an integrated luminosity of $125{\mathrm{pb}}^{-1\mathrm{}}$ of $\sqrt{s}=1.8\mathrm{TeV}p\overline{p}$ collisions. We obtain $m_t=168.4\mathrm{}\pm 12.3\left(\mathrm{stat}\right)\pm 3.6\left(\mathrm{syst}\right)\mathrm{GeV}{/c}^2$, consistent with the measurement obtained using single-lepton events. Combination of the single-lepton and dilepton results yields $m_t=172.0\mathrm{}\pm 7.5\mathrm{GeV}{/c}^2$.

We applied multiresolution wavelet analysis to the sequence of times between human heartbeats ( $R-R$ intervals) and have found a scale window, between 16 and 32 heartbeat intervals, over which the widths of the $R-R$ wavelet coefficients fall into disjoint sets for normal and heart-failure patients. This has enabled us to correctly classify every patient in a standard data set as belonging either to the heart-failure or normal group with 100% accuracy, thereby providing a clinically significant measure of the presence of heart failure from the $R-R$ intervals alone. Comparison is made with previous approaches, which have provided only statistically significant measures.

A mesoscopic superposition of quantum states involving radiation fields with classically distinct phases was created and its progressive decoherence observed. The experiment involved Rydberg atoms interacting one at a time with a few photon coherent field trapped in a high $Q$ microwave cavity. The mesoscopic superposition was the equivalent of an “ $\mathrm{atom}+\mathrm{measuring}\mathrm{apparatus}$” system in which the “meter” was pointing simultaneously towards two different directions—a “Schrödinger cat.” The decoherence phenomenon transforming this superposition into a statistical mixture was observed while it unfolded, providing a direct insight into a process at the heart of quantum measurement.

We demonstrate that high-order harmonics generated by an atom in intense laser field form trains of ultrashort pulses corresponding to different trajectories of electrons that tunnel out of the atom and recombine. Propagation in an atomic jet allows us to select one of these trajectories, leading to a train of pulses of extremely short duration.

We demonstrate the operation of a two-bit "controlled-NOT" quantum logic gate, which, in conjunction with simple single-bit operations, forms a universal quantum logic gate for quantum computation. The two quantum bits are stored in the internal and external degrees of freedom of a single trapped atom, which is first laser cooled to the zero-point energy. Decoherence effects are identified for the operation, and the possibility of extending the system to more qubits appears promising.

We have observed Bose-Einstein condensation of sodium atoms. The atoms were trapped in a novel trap that employed both magnetic and optical forces. Evaporative cooling increased the phase-space density by 6 orders of magnitude within seven seconds. Condensates contained up to 5×${10}^5$ atoms at densities exceeding ${10}^{14}$ ${\mathrm{cm}}^{-3\mathrm{}}$. The striking signature of Bose condensation was the sudden appearance of a bimodal velocity distribution below the critical temperature of ∼2μK. The distribution consisted of an isotropic thermal distribution and an elliptical core attributed to the expansion of a dense condensate.

An unknown quantum state ‖φ〉 can be disassembled into, then later reconstructed from, purely classical information and purely nonclassical Einstein-Podolsky-Rosen (EPR) correlations. To do so the sender, ‘‘Alice,’’ and the receiver, ‘‘Bob,’’ must prearrange the sharing of an EPR-correlated pair of particles. Alice makes a joint measurement on her EPR particle and the unknown quantum system, and sends Bob the classical result of this measurement. Knowing this, Bob can convert the state of his EPR particle into an exact replica of the unknown state ‖φ〉 which Alice destroyed.

The escape rate of an underdamped ($Q\approx 30$), current-biased Josephson junction from the zero-voltage state has been measured. The relevant parameters of the junction were determined in situ in the thermal regime from the dependence of the escape rate on bias current and from resonant activation in the presence of microwaves. At low temperatures, the escape rate became independent of temperature with a value that, with no adjustable parameters, was in excellent agreement with the zero-temperature prediction for macroscopic quantum tunneling.

We report the first observation of quantized energy levels for a macroscopic variable, namely the phase difference across a current-biased Josephson junction in its zero-voltage state. The position of these energy levels is in quantitative agreement with a quantum mechanical calculation based on parameters of the junction that are measured in the classical regime.