87 research outputs found
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
instead of the standard 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 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
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