Three-wire magnetic trap for direct forced evaporative cooling

We propose a simple three-wire-based magnetic trap potential for direct forced evaporative cooling of neutral atoms without using induced spin-flip technologies. We have devised a method for controlling the trap depth without sacrificing its frequencies by only varying wire currents and external magnetic fields. By having multiples of these wires on different levels integrated into an atom chip, it is possible to attain Bose-Einstein condensation without the conventional forced evaporation technique.

Figure 1

(Color online) Schematic of a H-wire trap pattern design in a two-dimensional plane accompanied with external bias magnetic fields $(B_{x0},B_{y0})$. The $x$-directional wire with a length of $L_0$ carries the same current $I_0$. The two $y$-directional wires with a length of $L_1$ and separation of $d$ carry the current $I_1$. All the wires have the same width of $W$ and height of $h$ (not shown).

Figure 2

(Color online) H-wire magnetic trap potential plots in all three ($x$, $y$, and $z$) dimensions are shown in (a), (b), and (c), respectively. The initial trap (solid, red) with trap frequencies of $(24,2253,2253)\mathrm{Hz}$ is obtained with the parameters $I_0=I_1=4\mathrm{A}$, $B_{x0}=0$, and $B_{y0}=40\mathrm{G}$. The final trap (dashed, blue) with trap frequencies of $(17,2114,2114)\mathrm{Hz}$ is obtained with the parameters $I_0=1\mathrm{A}$, $I_1=4\mathrm{A}$, $B_{x0}=0.64\mathrm{G}$, and $B_{y0}=20\mathrm{G}$.

Figure 3

(Color online) H-wire magnetic trap potential contour plots in $x\text{−}y$, $x\text{−}z$, and $y\text{−}z$ planes with the same parameters in Fig. 2. The initial trap is shown in (a1), (b1), and (c1). The final trap is shown in (a2), (b2), and (c2).

Figure 4

(Color online) Control parameters and trap frequencies during a forced evaporation by ramping down the $y$-bias field $B_{y0}$ from $40\text{to}10\mathrm{G}$ and holding $I_1=4\mathrm{A}$ constant. (a) The current $I_0$ and $x$-bias field $B_{x0}$ vs the $y$-bias field $B_{y0}$ during evaporation. (b) The longitudinal and transverse trap frequencies vs the trap depth during evaporation.