The discrete quantum properties of matter are manifest in a variety of phenomena. Any particle that is trapped in a sufficiently deep and wide potential well is settled in quantum bound states. For example, the existence of quantum states of electrons in an electromagnetic field is responsible for the structure of atoms, and quantum states of nucleons in a strong nuclear field give rise to the structure of atomic nuclei. In an analogous way, the gravitational field should lead to the formation of quantum states. But the gravitational force is extremely weak compared to the electromagnetic and nuclear force, so the observation of quantum states of matter in a gravitational field is extremely challenging. Because of their charge neutrality and long lifetime, neutrons are promising candidates with which to observe such an effect. Here we report experimental evidence for gravitational quantum bound states of neutrons. The particles are allowed to fall towards a horizontal mirror which, together with the Earth's gravitational field, provides the necessary confining potential well. Under such conditions, the falling neutrons do not move continuously along the vertical direction, but rather jump from one height to another, as predicted by quantum theory.

We demonstrate the controlled incorporation of P dopant atoms in Si (001) presenting a new path toward the creation of atomic-scale electronic devices. We present a detailed study of the interaction of PH3 with Si (001) and show that it is possible to thermally incorporate P atoms into Si (001) below the H desorption temperature. Control over the precise spatial location at which P atoms are incorporated was achieved using STM H-lithography. We demonstrate the positioning of single P atoms in Si with ∼ 1 nm accuracy and the creation of nanometer wide lines of incorporated P atoms.PACS numbers: 03.67. Lx, 68.37.Ef, The ability to control the location of individual dopant atoms within a semiconductor has enormous potential for the creation of atomic-scale electronic devices, including recent proposals for quantum cellular automata [1], single electron transistors [2] and solid-state quantum computers [3]. Current techniques for controlling the spatial extent of dopant atoms in Si rely on either ion implantation techniques, or dopant diffusion through optical or electron-beam patterned mask layers. While the resolution of these techniques continues to improve they have inherent resolution limits as we approach the atomicscale [4]. The work presented here looks beyond conventional techniques to position P dopant atoms with atomic-precision by using scanning tunneling microscopy (STM) based lithography on H passivated Si (001) surfaces [5,6] to control the adsorption and subsequent incorporation of single P dopant atoms into the Si (001) surface.First, we show the controlled adsorption of PH 3 molecules to STM-patterned areas of H-terminated Si (001) surfaces. In these studies, we have used the H-terminated surface as a reference where the intrinsic surface periodicity can be observed to identify both adsorbed PH 3 molecules [7] and the previously unobserved room temperature dissociation product, PH 2 . We then show, using low PH 3 dosed clean Si (001) surfaces, that both of these room temperature adsorbates can be completely dissociated using a critical anneal, and more importantly, that this results in the substitutional incorporation of individual P atoms into the top layer of the substrate. Finally, we combine these two results to demonstrate the spatially controlled incorporation of individual P dopant atoms into the Si (001) surface with atomicscale precision. Of crucial importance to this final result is that the anneal temperature for P atom incorporation lies below the H-desorption temperature, so that the Hresist layer effectively blocks any surface diffusion of P atoms before their incorporation into the substrate surface.Figures 1(a) -1(c) demonstrate the flexibility of STM H-lithography to create different sized regions of bare Si (001) surface. As we will show, these regions can be used not only as a template for dopant incorporation but also to aid in fundamental studies of surface reactions. Figures 1(a) and 1(b) show the creation of both large areas (200 × 30 nm 2 ) and parallel, nanometer-wide lines...

The lowest stationary quantum state of neutrons in the Earth's gravitational field is identified in the measurement of neutron transmission between a horizontal mirror on the bottom and an absorber/scatterer on top. Such an assembly is not transparent for neutrons if the absorber height is smaller than the ''height'' of the lowest quantum state.

We present a complete fabrication process for the creation of robust nano-and atomic-scale devices in silicon using a scanning tunneling microscope (STM). In particular we develop registration markers which, in combination with a custom-designed STM-scanning electron microscope (SEM) system, solve one of the key fabrication problems − connecting the STM-patterned buried phosphorus-doped devices, fabricated in the ultrahigh vacuum environment, to the outside world. The first devices demonstrate the feasibility of this technology and confirm the presence of quantum confinement in devices as electron propagation is laterally constricted by STM patterning.