Bose–Einstein condensation of metastable helium in a bi-planar quadrupole Ioffe configuration trap R.G. Dall, A.G. Truscott * ARC Centre of Excellence for Quantum-Atom Optics, Research School of Physical Sciences and Engineering, Australian National University, Canberra, ACT 0200, Australia Received 25 May 2006; received in revised form 25 August 2006; accepted 9 September 2006 Abstract Using a novel magnetic trapping geometry we have evaporatively cooled metastable helium atoms to form a Bose–Einstein conden- sate containing approximately one million atoms. This is only the fourth demonstration of a metastable condensate and the first real- isation of a BEC in a bi-planar quadrupole Ioffe configuration magnetic trap. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Metastable helium; Bose–Einstein condensation; Magnetic trapping 1. Introduction The first realizations of Bose–Einstein condensation (BEC) in a dilute gas of weakly interacting atoms [1–3], have led to an explosion of research in the field of quantum degenerate gases. These first demonstrations were all achieved with alkali atoms in their true electronic ground state. In 2001, two groups [4,5] successfully created the worlds first metastable BEC, comprising metastable 2 3 S 1 helium atoms (He * ). It had long been thought such an achievement would be impossible due to Penning ionisa- tion: two colliding He * atoms have a combined internal energy of 40 eV which is sufficient to ionize one of the collision partners while transferring the other to the ground state. However, as predicted by Shlyapnikov et al. [6], Pen- ning losses are reduced by four orders of magnitude in a magnetic trap of He * , compared to an unpolarised sample, and thus these losses did not stop the production of a He * BEC. The large internal energy of metastables makes them interesting candidates for BEC, allowing single atom detec- tion with high spatial (lm) and temporal resolution (ns). Recently, Schellekens et al. made use of this unique prop- erty to demonstrate the Hanbury–Brown Twiss effect with He * atoms [7]. Another unique property of a He * BEC is that it produces ions due to Penning ionisation. This pro- cess allows the experimenter a very sensitive tool, to non- destructively monitor the condensate in real time. Seidelin et al. were able to map out the evolution of a BEC, from formation to decay, using this unique tool [8]. Besides the unique detection possibilities that He * offers, it is also attractive to the spectroscopist due to its relatively simple atomic structure. He * has only two electrons and no hyperfine interaction, and thus its energy levels can be cal- culated with a high degree of accuracy. In 2003, Le ´onard et al. [9] used photoassociation to spectroscopically demon- strate the presence of long range molecular bound states of He * . The experimentally determined binding energies were in excellent agreement with theoretical predictions. More recently, spectroscopic measurements of the s-wave scatter- ing length of He * have been achieved with unprecedented accuracy by Leduc and co-workers [10]. In this paper, we report on our realisation of a BEC of He * . This represents only the fourth such achievement of a metastable BEC. Our experimental system is quite different 0030-4018/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.optcom.2006.09.031 * Corresponding author. Tel.: +61 2 61253626. E-mail address: andrew.truscott@anu.edu.au (A.G. Truscott). www.elsevier.com/locate/optcom Optics Communications 270 (2007) 255–261