Heavy atom quantum diffraction by scattering from surfaces

Typically one expects that when a heavy particle collides with a surface, the scattered angular distribution will follow classical mechanics. The heavy mass assures that the de Broglie wavelength of the incident particle in the direction of the propagation of the particle (the parallel direction) will be much shorter than the characteristic lattice length of the surface, thus leading to a classical description. Recent work on molecular interferometry has shown that by increasing the perpendicular coherence length, one may observe interference of very heavy species passing through a grating. Here we show, using quantum mechanical simulations, that the same effect will lead to quantum diffraction of heavy particles colliding with a surface. We find that the effect is robust with respect to the incident energy, the angle of incidence and the mass of the particle. It may also be used to verify the quantum nature of the surface and its fluctuations at very low temperatures.Comment: 9 pages, 3 figure

Cavity-Induced Quantum Interference and Collective Interactions in van der Waals Systems

The central topic of this letter is to show that light-matter hybridization not only gives rise to novel dynamic responses but can also modify intermolecular interactions and induce new structural order. Using the van der Waals (vdW) system in an optical cavity as an example, we predict the effects of interference and collectivity in cavity-induced many-body dispersion interactions. Specifically, the leading order correction due to cavity-induced quantum fluctuations leads to 3-body and 4-body vdW interactions, which can align intermolecular vectors and are not pairwise additive. In addition, the cavity-induced dipole leads to a single-molecule energy shift that aligns individual molecules, and a pair-wise interaction that scales as $R^{-3}$ instead of the standard $R^{-6}$ distance scaling. The coefficients of all these cavity-induced corrections depend on the cavity frequency and are renormalized by the effective Rabi frequency, which in turn depends on the particle density. Finally, we study the interaction of the vdW system in a cavity with an external object and find a significant enhancement in the interaction range due to modified distance scaling laws. These theoretical predictions suggest the possibility of cavity-induced nematic or smectic order and may provide an essential clue to understanding intriguing phenomena observed in optical cavities, such as strongly-modified ground-state reactivity, ion transport and solvent polarity

Time averaging of weak values - consequences for time-energy and coordinate-momentum uncertainty

Using the quantum transition path time probability distribution we show that time averaging of weak values leads to unexpected results. We prove a weak value time energy uncertainty principle and time energy commutation relation. We also find that time averaging allows one to predict in advance the momentum of a particle at a post selected point in space with accuracy greater than the limit of $\hbar /2$ as dictated by the uncertainty principle. This comes at a cost - it is not possible at the same time to predict when the particle will arrive at the post selected point. A specific example is provided for one dimensional scattering from a square barrier.Comment: 14 pages, 2 figure