We describe some properties of consistent sets of histories in the Gell-Mann–Hartle formalism, and give an example to illustrate that one cannot recover the standard predictions, retrodictions, and inferences of quasiclassical physics using the criterion of consistency alone.

We report a new type of restoration of macroscopic isotropy (homogenization) in fractals with microscopic anisotropy. The phenomenon is observed in various physical setups, including diffusion, random walks, resistor networks, and Gaussian field theories. The mechanism is unique in that it is absent in uniform media, while universal in that it is observed in a wide class of fractals.

A Comment on the Letter by Philip Pechukau, Phys. Rev. Lett. 73, 1060 (1994). The authors of the Letter offer a Reply.

A Reply to the Comment by Robert Alicki.

Divergent weak-coupling perturbation expansions for physical quantities can be converted into sequences of uniformly and exponentially fast converging approximations. This is possible with the help of an additional variational parameter to be optimized order by order. The uniformity of the convergence for any coupling strength allows us to take all expressions directly to the strong-coupling limit, yielding a simple calculation scheme for the coefficients of convergent strong-coupling expansions. As an example, we determine these coefficients for the ground state energy of the anharmonic oscillator up to 22nd order with a precision of about 20 digits.

A new cluster algorithm based on invasion percolation is described. The algorithm samples the critical point of a spin system without a priori knowledge of the critical temperature and provides an efficient way to determine the critical temperature and other observables in the critical region. The method is illustrated for the two- and three-dimensional Ising models. The algorithm equilibrates spin configurations much faster than the closely related Swendsen-Wang algorithm.

We have developed a novel interferometer for atom de Broglie waves, where amplitude division and recombination is achieved by diffraction at standing light waves operating as phase gratings. Our new atom interferometer is the exact mirror image of interferometers for light, with the roles of atoms and photons interchanged, and it directly demonstrates coherence of the diffraction of atomic waves at standing light waves. Easy manipulation of the phase, intensity, and polarization of the standing light wave permits novel studies of atomic coherence properties.

We have constructed an atom interferometer by Bragg deflecting a collimated beam of metastable neon atoms from three parallel standing waves. Interference fringes have been observed using atoms Bragg scattered at up to the third order, giving a maximum of $6ħk$ transverse momentum difference between the two arms of the interferometer. In the first order case we have achieved a fringe contrast of 62% and a peak to peak signal of 1700 atoms/s. We believe this to be the highest fringe contrast that has been achieved in atom interferometers.

We derive the time-dependent wave function for one particle in the company of $N-1\mathrm{}$ other particles using the method of iterated projection. Using this approach, we confirm the general philosophy of describing a quantum system by a flow component and another component which may be given various descriptions as stochastic, heat bath, or quantum jump processes. The possible equivalence of the Breuer-Petruccione reduced system dynamics [Phys. Rev. Lett. 74, 3788 (1995)] and ours is explored.

We derive the quantum phase accompanying a neutral particle (with no permanent electric dipole moment) moving in an area where a nonuniform electric field and a uniform magnetic field are simultaneously applied. Such a quantum phase can be ascribed to the sum of the Aharonov-Bohm phases of the charges constituting the neutral particle. An experimental configuration much more practical than a previous suggestion is proposed to test for the phase. The possible nonzero superfluid velocity in the ground state of the ${}^4\mathrm{He}$ condensate is theoretically demonstrated.

In contrast to what happens in systems at thermodynamic equilibrium, microscopic dynamics plays an essential role in the macroscopic behavior of nonequilibrium systems. Usually, continuum descriptions of nonequilibrium systems do not model accurately enough this microscopic dependence. For a broad class of nonequilibrium lattice models, defined through a master equation, we construct a continuous representation, i.e., a Fokker-Planck equation. It is constructed in such a way that its deterministic stationary states and the fluctuations in a neighborhood of them are exactly represented. Therefore any future analysis based on this new Fokker-Planck equation will lead to more confident results.

The relative frequency of Hg and Cs mgnetometers is monitored as a function of the orientation of the applied magnetic field with respect to the fixed stars. The observed stability of the relative frequency limits electron and nucleon local Lorentz invariance violating effects to less than 200 μHz and 110 nHz, respectively. These results represent an improvement over the best published results by an order of magnitude for electron effects and by a factor of 240 for nuclear effects. The result also sets an upper limit of 200 eV on the Fermi level of a degenerate remnant neutrino background.

A continuum limit of the non-Hermitian spin-1/2 chain, conjectured recently to belong to the universality class of the noisy Burgers or, equivalently, Kardar-Parisi-Zhang equation, is obtained and analyzed. The Galilean invariance of the Burgers equation is explicitly realized in the operator algebra. In the quasiclassical limit we find nonlinear soliton excitations exhibiting the $\omega \propto k^z$ dispersion relation with dynamical exponent $z=3\mathrm{}/2$.

A Comment on the Letter by Lucien Hardy, Phys. Rev. Lett. 73, 2279 1994. The authors of the Letter offer a Reply.

A Comment on the Letter by Lucien Hardy, Phys. Rev. Lett. 73, 2279 (1994). The authors of the Letter offer a Reply.

A Reply to the Comment by Lev Vaidman and D. M. Greenberger, M. A. Horne and A. Zeilinger.

A Comment on the Letter by J. Daicic, N. E. Frankel, and V. Kowalenko, Phys. Rev. Lett. 71, 1779 (1993). The authors of the Letter offer a Reply.

A Reply to the Comment by Per Elmfors et al.

We propose a new method of solving the traveling salesman problem in this Letter. A new technique, whose concept comes from real space renormalization theory, is introduced to solve the combinatorial problem of operation research. Examples of the calculation applied from the 48-cities to the 532-cities problem and a theoretical estimate of the computational effort are presented. It was found that the present method belongs to the group of the fastest computing algorithm of the traveling salesman problem. Throughout this work we show an interesting cross of operation research and statistical physics.