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Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

Trapping Atoms with a Persistent Supercurrent Atom Chip

Christoph Hufnagel, T. Mukai, Fujio Shimizu

Published Jun 1, 2007• 0 citations
Publisher

Abstract

In this presentation we report an achievement of a persistent supercurrent atom chip and trapping87Rb atoms in the vicinity of a cold surface. Persistent supercurrent, up to 2.5 A without Joule heating, was switched on and off by using an on-chip thermal switch that was operated with a laser and a magnetic field. An intensity of the induced supercurrent was controlled by the magnitude of the initially applied z-bias field. We present our experimental results on the characteristics of our atom trap including stability, decoherence time, and influence of the chip surface.

DOI
10.1109/cleoe-iqec.2007.4386720

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In this presentation we report an achievement of a persistent supercurrent atom chip and trapping87Rb atoms in the vicinity of a cold surface. Persistent supercurrent, up to 2.5 A without Joule heating, was switched on and off by using an on-chip thermal switch that was operated with a laser and a magnetic field. An intensity of the induced supercurrent was controlled by the magnitude of the initially applied z-bias field. We present our experimental results on the characteristics of our atom trap including stability, decoherence time, and influence of the chip surface.
Rubidium-87 atoms are trapped in an Ioffe-Pritchard potential generated with a persistent supercurrent that flows in a loop circuit patterned on a sapphire surface. The superconducting circuit is a closed loop made of a 100 microm wide molecular-beam epitaxy-grown MgB2 stripe carrying a supercurrent of 2.5 A. To control the supercurrent in the stripe, an on-chip thermal switch operated by a focused argon-ion laser is developed. The switch operates as an on/off switch of the supercurrent or as a device to set the current to a specific value with the aid of an external magnetic field. The current can be set even without an external source if the change is in the decreasing direction.
A persistent-supercurrent atom chip is a quantum device designed with a view to transcending the limits of conventional technologies by employing some of the significant properties of quantum mechanics.We have applied this novel technique to achieve an atomic gas in a macroscopic quantum state in the vicinity of a solid-state surface.In this article, we review a technique for making an extremely stable Bose-Einstein condensate above a chip surface and describe our attempts to overcome several unpredicted problems introduced by superconductivity.
Ultra-cold neutral atoms and Bose-Einstein condensates (BECs) offer fascinating possibilities for quantum information processing. Long decoherence times, easy qubit addressing and the potential for scalability are some advantages. Storing and manipulating atoms in magnetic microtraps or 'Atom Chips' provides a promising base on which quantum logic operations could be performed. A primary source of decoherence in atom chip experiments arises from the interaction of the micro-Kelvin atoms with the room temperature chip surface. We have experimentally investigated these interactions and observe two interesting effects. Firstly, ultra-cold clouds are seen to fragment into clumps when brought within 100 microns of the chip surface. Secondly, the lifetime of atom clouds is seen to drop off near the surface due to spin flip transitions. These are caused by radio-frequency thermal fluctuations of the magnetic field as predicted but not previously observed.
Atom chips are micro-fabricated devices which create versatile magnetic potentials for trapping, cooling and controlling ensembles of ultra-cold atoms. Advancing from the typical atom chips, currents from superconducting vortices are used to trap and manipulate the ultra-cold atoms in our experiments. The superconducting vortex traps can be configured by controlling strength and pulse time of external magnetic fields together with bias fields. In order to fully utilize reconfigurability, superconducting vortices are optically manipulated with laser light to generate desired vortex patterns with this tailored trapping potentials for ultra-cold atoms are created. We have carried out heat diffusion simulations of laser patterns and characterized laser power and pulse time to effectively configure the desired vortex potentials. We have also successfully manipulated vortex matter optically to create arbitrary vortex patterns and ring potentials for cold atoms to utilize in quantum simulations and on-chip matter wave interferometry applications. Moreover, cold atoms could be used as a sensitive probe to examine magnetic field distribution of the superconducting vortices and we have used this technique to experimentally verify the resulting magnetic potentials of superconducting vortices after optical manipulation. v First of all, I would like to express my heartfelt gratitude and appreciation to my teacher and mentor, Prof.
We investigate superconducting chip structures for trapping and manipulating atoms. These structures are based on the average magnetic field of vortices induced in a type-II superconducting thin film. This magnetic field is the critical ingredient of the demonstrated vortex-based atom trap, which operate without transport current. We employ the hysteretic behavior of a superconducting thin film in the remanent state to generate different traps and flexible magnetic potentials for ultra-cold atoms. The experimental realization can be described by the Bean’s critical-state method to model the vortex field through mesoscopic super currents induced in the thin strip. Various vortex patterns can be obtained by programming different loading-field and transport current sequences. Furthermore we will discuss the expected enhanced lifetime of atoms trapped close to a superconducting surface in comparison with a metallic surface.