Stable, Tightly Confining Magnetic Trap for Evaporative Cooling of Neutral Atoms

Abstract

We describe a new type of magnetic trap whose time-averaged, orbiting potential (TOP) supplies tight and harmonic confinement of atoms. The TOP trap allows for long storage times even for cold atom samples by suppressing the loss due to nonadiabatic spin Hips which limits the storage time in an ordinary magnetic quadrupole trap. In preliminary experiments on evaporative cooling of ' Rb atoms in the TOP trap, we obtain a phase-space density enhancement of up to 3 orders of magnitude and temperatures as low as 200 nK. PACS numbers: 32.80.Pj, 42.50.Vk, 85.70.Nk Laser cooling and trapping of neutral atoms can provide up to 15 orders of magnitude phase-space density compression in alkali vapors [I]; however, optical processes limiting density [2] and temperature [3] have obstructed efforts to optically cool an atom sample directly to the Bose-Einstein condensation (BEC) phase transition. Evaporative cooling [4] in a purely magnetic trap offers an appealing, nonoptical cooling mechanism that can enhance the phase-space density of an optically precooled sample by orders of magnitude [5]. The resulting atom

Optically plugged quadrupole trap for Bose-Einstein condensates

“…Unfortunately, by itself this trap is not so useful for evaporative cooling-within a region of 1 − 2µm radius near the magnetic field zero at the trap center, the atoms can spontaneously undergo spin flips and are lost from the trap [15]. This Majorana loss can be eliminated if one removes the field zero from the cloud, for example, using a fast, rotating bias field [15,16], or alternately, using a Ioffe-Pritchard design which has a finite bias field at the trap minimum [13]. Our approach is based on an idea of Ketterle to use the optical dipole force of a blue-detuned laser beam to repel atoms from the region containing the hole [1].…”

Dynamics of rotating Bose–Einstein condensates probed by Bragg scattering

“…It consists of a rapidly rotating magnetic bias field superimposed on a static quadrupole magnetic trap. The net effect is to move the magnetic field zero outside of the cloud, thus preventing nonadiabatic spin flips [16], and resulting in a time-averaged potential…”

“…In our experiments we produce a sodium BEC with typically 1 − 3 × 10 6 atoms in a time-averaged orbiting potential (TOP) trap [16], according to the method described in [22]. Parameters for the trap are a radial gradient B ′ ρ = 12 Gauss/cm and a bias rotation of ω T OP = 2π × 5 kHz.…”

Secondary Phase Transition of Ising Model

“…In addition, we notice that the lattice-spin phonons can be regarded as ideal Bose gas, its special property at low temperature should be reviewed. Since Bose-Einstein condensation (BEC) in dilute atomic gases has produced by experimental groups in 1995 [2][3][4][5], the experimental observations and relevant theoretical explanations for BEC phenomena in diverse physical systems have successively been reported [6][7][8][9][10][11][12][13][14], among them the interesting issues for us are that refer to BEC of magnons [8][9][10][11][12]. The similarity between magnons and lattice-spin phonons enable us to believe that an Ising model, as an example of ferromagnet, may experience a BEC phase transition at ultralow temperature, which will determine a characteristic of magnetic saturation.…”