Abstract
We present an analysis of magnetic traps for ultracold atoms based on current-carrying wires with sub-micron dimensions. We analyze the physical limitations of these conducting wires as well as how such miniaturized magnetic traps are affected by the nearby surface due to tunneling to the surface, surface thermal noise, electron scattering within the wire and the Casimir–Polder force. We show that wires with cross sections as small as a few tens of nanometers should enable robust operating conditions for coherent atom optics (e.g. tunneling barriers for interferometry). In particular, trap sizes of the order of the de Broglie wavelength become accessible, based solely on static magnetic fields, thereby bringing the atomchip a step closer to fulfilling its promise of a compact device for complex and accurate quantum optics with ultracold atoms.
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GENERAL SCIENTIFIC SUMMARY Introduction and background. The atom chip is a micro-fabricated, integrated device in which electric, magnetic and optical fields can confine, control and manipulate ultracold atoms. In current chips the system of interest (the electron) is manipulated inside the chip, but in the atom chip the system of interest is trapped micrometers outside the chip, so that isolation enables quantum coherence. Small atom–chip separations are advantageous for a number of reasons. However, interactions with the nearby surface become important in such small separations, and they can limit the minimal distance from the surface.
Main results. The main aim of the current work is to suggest new ways of overcoming the effects limiting atom–surface separations. We present an analysis of magnetic traps for ultracold atoms based on current-carrying wires with sub-micron dimensions. The physical limitations of these wires are analyzed. We study the effects of surface thermal noise, electron scattering within the wire, and the Casimir-Polder force. We show that wires with cross sections as small as a few tens of nanometers should enable robust operating conditions for coherent atom optics. This work thus brings atom chips into the realm of nanometer science and technology.
Wider implications. Atom chips may form the basis for quantum computers, quantum communications, ultra-precision clocks, navigation systems and magnetic sensors, not to mention being a novel tool for gaining further insight into the foundations of quantum theory. The work presented here describes how some of the limiting factors may be overcome, thereby bringing the atom chip a step closer to fulfilling its promise of a compact device for complex and accurate quantum optics.
Figure 1. Scanning electron microscope (SEM) image of a 2μ m long, 20 nm thick and 50 nm wide gold wire.
Figure 2. An isopotential surface of the trapping potential for an energy 0.1μ K above the trap minimum. The longitudinal axis is compressed by a factor of 50 for a better view. The potential corrugation is due to the trapping wire edge roughness. The inset shows a 1D cut of the potential above the trap center, with the energy of the isopotential surface shown by the dashed red line.