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arXiv:cond-mat/0507129 · Review of Scientific Instruments

Partially ferromagnetic electromagnet for trapping and cooling neutral atoms to quantum degeneracy

M. Fauquembergue, J.-F. Riou, William Guerin, S. A. Rangwala, F. Moron, André Villing, Yann Le Coq, Philippe Bouyer, Alain Aspect, Michel Lecrivain

Published Oct 1, 2005• 8 citations
arXivHTMLPDF

Abstract

We have developed a compact partially ferromagnetic electromagnet to produce an Ioffe-Pritchard trap for neutral atoms. Our structure permits strong magnetic confinement with low power consumption. Compared to the previous iron-core electromagnet [B. Desruelle, V. Boyer, P. Bouyer, G. Birkl, M. Lécrivain, F. Alves, C. Westbrook, and A. Aspect, Eur. Phys. J. D 1, 255 (1998)], it allows for easy compensation of remnant fields and very high stability, along with cost-effective realization and compactness. We describe and characterize our apparatus and demonstrate trapping and cooling of Rb87 atoms to quantum degeneracy. Pure Bose-Einstein condensates containing 106 atoms are routinely realized on a half-minute cycle. In addition we test the stability of the magnetic trap by producing atom lasers.

DOI
10.1063/1.2090407

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We have developed a compact partially ferromagnetic electromagnet to produce an Ioffe-Pritchard trap for neutral atoms. Our structure permits strong magnetic confinement with low power consumption. Compared to the previous iron-core electromagnet [B. Desruelle, V. Boyer, P. Bouyer, G. Birkl, M. Lécrivain, F. Alves, C. Westbrook, and A. Aspect, Eur. Phys. J. D 1, 255 (1998)], it allows for easy compensation of remnant fields and very high stability, along with cost-effective realization and compactness. We describe and characterize our apparatus and demonstrate trapping and cooling of Rb87 atoms to quantum degeneracy. Pure Bose-Einstein condensates containing 106 atoms are routinely realized on a half-minute cycle. In addition we test the stability of the magnetic trap by producing atom lasers.
Since its first observation in 1995, Bose-Einstein condensation (BEC) experiments in dilute gases have been performed with only a few different kinds of magnetic traps. We have performed a BEC experiment with /sup 87/Rb atoms in a Ioffe-Pritchard magnetic potential, which opens up the possibility to study, e.g., Bose-Einstein condensates released in only one dimension. Our trap consists of a clip-like coil, which generates a pure two-dimensional (2D) quadrupole field for radial confinement. The axial confinement is provided by two plane pinch coils inside the clip-coil. These two coils create a bottle field. Two additional Helmholtz coils on the same symmetry axis are used to compensate the homogeneous part of the bottle field. By continuously varying the currents through the coils, the trapping potential can be changed from a 3D spherical harmonic to a 2D linear potential. The change can be done adiabatically or nonadiabatically by switching off the axial confinement slowly, or instantaneously respectively. This opens up the possibility to study 1D nonlinear atom optics. In combination with, e.g., far detuned light sheets, a Fabry-Perot type interferometer for a condensate might be realizable. Our experiments are performed in a vacuum system with two magneto-optical traps, which serves as the source of cold atoms for the magnetic trap. 10/sup 9/ atoms are captured in less than one minute. RF-induced evaporative cooling is used to increase the phase space density of the trapped atomic cloud. The BEC phase transition occurs at a temperature of 550 nK with 10/sup 6/ particles in the trap. Pure condensates with more than 10/sup 5/ atoms were produced.
Summary form only given.Since its first observation in 1995, Bose-Einstein condensation (BEC) experiments in dilute gases have been performed with only a few different kinds of magnetic traps. We have performed a BEC experiment with /sup 87/Rb atoms in a Ioffe-Pritchard magnetic potential, which opens up the possibility to study, e.g., Bose-Einstein condensates released in only one dimension. Our trap consists of a clip-like coil, which generates a pure two-dimensional (2D) quadrupole field for radial confinement. The axial confinement is provided by two plane pinch coils inside the clip-coil. These two coils create a bottle field. Two additional Helmholtz coils on the same symmetry axis are used to compensate the homogeneous part of the bottle field. By continuously varying the currents through the coils, the trapping potential can be changed from a 3D spherical harmonic to a 2D linear potential. The change can be done adiabatically or nonadiabatically by switching off the axial confinement slowly, or instantaneously respectively. This opens up the possibility to study 1D nonlinear atom optics. In combination with, e.g., far detuned light sheets, a Fabry-Perot type interferometer for a condensate might be realizable. Our experiments are performed in a vacuum system with two magneto-optical traps, which serves as the source of cold atoms for the magnetic trap. 10/sup 9/ atoms are captured in less than one minute. RF-induced evaporative cooling is used to increase the phase space density of the trapped atomic cloud. The BEC phase transition occurs at a temperature of 550 nK with 10/sup 6/ particles in the trap. Pure condensates with more than 10/sup 5/ atoms were produced.
We demonstrate Bose-Einstein condensation of rubidium atoms in a simple low-power magnetic trap. This trap combines the quadrupole with the Ioffe configuration (QUIC trap) and consists of just three coils. Magneto-optically trapped 87Rb{}^{87}\mathrm{Rb}87Rb atoms are first loaded into the linear trapping potential of a magnetic quadrupole, which is then converted into the parabolic geometry of an Ioffe trap. During this process two spherical quadrupole traps with perpendicular axes merge and the trapped atomic cloud moves close to the magnetic field producing coils, resulting in tight confinement of the atoms while the power dissipation of the trap remains low. The magnetically trapped atoms are cooled to below the phase transition of Bose-Einstein condensation by rf-induced evaporation.
The apparatus and procedure required to generate a pure Bose-Einstein condensate (BEC) consisting of about half a million 87Rb atoms at a temperature of <60 nK with a phase density of >54 is described. The atoms are first laser cooled in a vapour cell magneto-optical trap (MOT) and subsequently transferred to an ultra-low pressure MOT. The atoms are loaded into a QUIC trap consisting of a pair of quadrupole coils and a Ioffe coil that generates a small finite magnetic field at the trap energy minimum to suppress Majorana transitions. Evaporation induced by an RF field lowers the temperature permitting the transition to BEC to be observed by monitoring the free expansion of the atoms after the trapping fields have been switched off.PACS Nos.: 03.75.Fi, 05.30.Jp, 32.80.Pj, 64.60.–i
Summary form only given. We have developed an apparatus for producing BEC that allows for very high confinements with very low power. Our system is based on the use of an iron core electromagnet. This allows us to achieve BEC in high bias fields, or with very high aspect ratios. The latest developments of our electromagnet design should allow us to realize quasi-1D or 1D condensates. We used different evaporation techniques (3-RF-knives, hyperfine transition, sympathetic cooling) to overcome the interruption of evaporative cooling in high bias fields for the F=2, m=2 ground state. This allows for multiple independent condensates that can be studied with an output RF coupler. We realized an atom laser for atoms initially in F=1, m=-1 and coupled it into a magnetic atomic cavity by transferring the atoms into the F=2, m=0 state (a trapping state at our bias field). The patterns observed in such a cavity result from the beat note between several cavity modes and are a signature of the high coherence of the initial atom layer.
We describe experimental setups for producing large Bose-Einstein condensates of Na23 and Rb87. In both, a high-flux thermal atomic beam is decelerated by a Zeeman slower and is then captured and cooled in a magneto-optical trap. The atoms are then transferred into a cloverleaf-style Ioffe-Pritchard magnetic trap and cooled to quantum degeneracy with radio-frequency-induced forced evaporation. Typical condensates contain 20×106 atoms. We discuss the similarities and differences between the techniques used for producing large Rb87 and Na23 condensates in the context of nearly identical setups.