Radio-frequency spectroscopy of a linear array of Bose-Einstein condensates in a magnetic lattice

Abstract

We report site-resolved radio-frequency spectroscopy measurements of Bose-Einstein condensates of 87 Rb atoms in about 100 sites of a one-dimensional (ID) 10-/rm-period magnetic lattice produced by a grooved magnetic film plus bias fields. Site-to-site variations of the trap bottom, atom temperature, condensate fraction, and chemical potential indicate that the magnetic lattice is remarkably uniform, with variations in the trap bottoms of only ± 0.4 mG. At the lowest trap frequencies (radial and axial frequencies of 1.5 kHz and 260 Hz, respectively), temperatures down to 0.16 /iK are achieved in the magnetic lattice, and at the smallest trap depths (50 kHz) condensate fractions up to 80% are observed. With increasing radial trap frequency (up to 20 kHz, or aspect ratio up to ~80) large condensate fractions persist, and the highly elongated clouds approach the quasi-1D Bose gas regime. The temperature estimated from analysis of the spectra is found to increase by a factor of about 5, which may be due to suppression of rethermalizing collisions in the quasi-1D Bose gas. Measurements for different holding times in the lattice indicate a decay of the atom number with a half-life of about 0.9 s due to three-body losses and the appearance of a high-temperature (~1.5 pK ) component which is attributed to atoms that have acquired energy through collisions with energetic three-body decay products.

Magnetic lattices for ultracold atoms and degenerate quantum gases

“…The effect of temperature is to change both the width of the broad thermal cloud component and the fraction of atoms in the condensate. Adapted from [35] Radiofrequency spectra taken simultaneously for all atom clouds across the central region of the magnetic lattice showed similar bimodal distributions to Fig. 2 with site-to-site variations in the above quantities that were consistent with the measurement errors ( Fig.…”

“…The fits to the data points in Fig. 2 are based on a selfconsistent mean-field model for a BEC plus thermal cloud convolved with a Gaussian magnetic noise function (FWHM=4.3 kHz) [35]. The model includes the repulsive interaction among atoms in the BEC and in the thermal cloud and the mutual interaction between them but neglects the kinetic energy of the condensate atoms via the Thomas-Fermi approximation and the effects of gravity sag in the tight magnetic traps.…”

“…An alternative approach for producing periodic lattices for trapping ultracold atoms involves the use of arrays of magnetic microtraps created by patterned magnetic films [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36], current-carrying conductors [37][38][39][40], nanomagnetic domain walls [41], vortex arrays in superconducting films [42] or pulsed gradient magnetic fields [43,44]. In the present mini-review we focus on recent developments in the trapping of ultracold atoms in magnetic lattices of microtraps based on patterned magnetic films.…”

Addressed qubit manipulation in radio-frequency dressed lattices

“…This can be achieved by using two-dimensional conducting materials such as 2D electron gases and graphene [33]. Similarly, thin patterned layers of permanent magnets can be employed as sources of static magnetic field, which, in principle, have reduced levels of noise associated with larger material resistivity [34]. A positive indication of this trend is the measurement of coherence times above 1 s at distances of 9 m m from a chip surface unprocessed to reduce field fluctuations [35].…”

“…A positive indication of this trend is the measurement of coherence times above 1 s at distances of 9 m m from a chip surface unprocessed to reduce field fluctuations [35]. Likewise, noise-sensitive gates can make an exceptional noise spectrum analyser capable for characterising and distinguishing various noise process [34,36]. A potential drawback of the our scheme is the use of field sensitive states to encode the qubit, which make them sensitive to magnetic field noise.…”