Static Magnetic Trap Research Articles

High-Q Magnetic Levitation and Control of Superconducting Microspheres at Millikelvin Temperatures.

We report the levitation of a superconducting lead-tin sphere with 100 μm diameter (corresponding to a mass of 5.6 μg) in a static magnetic trap formed by two coils in an anti-Helmholtz configuration, with adjustable resonance frequencies up to 240Hz. The center-of-mass motion of the sphere is monitored magnetically using a dc superconducting quantum interference device as well as optically and exhibits quality factors of up to 2.6×10^{7}. We also demonstrate 3D magnetic feedback control of the motion of the sphere. The setup is housed in a dilution refrigerator operating at 15mK. By implementing a cryogenic vibration isolation system, we can attenuate environmental vibrations at 200Hz by approximately 7 orders of magnitude. The combination of low temperature, large mass, and high quality factor provides a promising platform for testing quantum physics in previously unexplored regimes with high mass and long coherence times.

Low-energy collisions between carbon atoms and oxygen molecules in a magnetic trap

Trapping of atoms and molecules in electrostatic, magnetic and optical traps has enabled studying atomic and molecular interactions on a timescale of many seconds, allowing observations of ultra-cold collisions and reactions. Here we report the first magnetic deceleration and trapping of neutral carbon atoms in a static magnetic trap. When co-trapping the carbon atoms with oxygen molecules in a superconducting trap, the carbon signal decays in a non-exponential manner, consistent with the decay model describing losses resulting from atom-molecule collisions. Our findings pave the way to studying both elastic and inelastic collisions of species that cannot be laser cooled, and specifically may facilitate the observation of reactions at low temperatures, such as C + O2 → CO + O, which is important in interstellar chemistry.

High phase space density loading of a falling magnetic trap

Loading an ultra-cold ensemble into a static magnetic trap involves unavoidable loss of phase space density when the gravitational energy dominates the kinetic energy of the ensemble. In such a case the gravitational energy is transformed into heat, making a subsequent evaporation process slower and less efficient. We apply a high phase space loading scheme on a sub-doppler cooled ensemble of Rubidium atoms, with a gravitational energy much higher than its temperature of $1~\rm{\mu K}$. Using the regular configuration of a quadrupole magnetic trap, but driving unequal currents through the coils to allow the trap center to fall, we dissipate most of the gravitational energy and obtain a 20-fold improvement in the phase space density as compared to optimal loading into a static magnetic trap. Applying this scheme, we start an efficient and fast evaporation process as a result of the sub-second thermalization rate of the magnetically trapped ensemble.

Coulomb structures of charged macroparticles in static magnetic traps at cryogenic temperatures

Electrically charged (up to 107e) macroscopic superconducting particles with sizes in the micrometer range confined in a static magnetic trap in liquid nitrogen and in nitrogen vapor at temperatures of 77–91 K are observed experimentally. The macroparticles with sizes up to 60 μm levitate in a nonuniform static magnetic field B ~ 2500 G. The formation of strongly correlated structures comprising as many as ~103 particles is reported. The average particle distance in these structures amounts to 475 μm. The coupling parameter and the Lindemann parameter of these structures are estimated to be ~107 and ~0.03, respectively, which is characteristic of strongly correlated crystalline or glasslike structures.

Accumulation of Stark-decelerated NH molecules in a magnetic trap

Here we report on the accumulation of ground-state NH molecules in a static magnetic trap. A pulsed supersonic beam of NH (a1Δ) radicals is produced and brought to a near standstill at the center of a quadrupole magnetic trap using a Stark decelerator. There, optical pumping of the metastable NH radicals to the X3Σ− ground state is performed by driving the spin-forbidden A3Π ← a1Δ transition, followed by spontaneous A → X emission. The resulting population in the various rotational levels of the ground state is monitored via laser induced fluorescence detection. A substantial fraction of the ground-state NH molecules stays confined in the several milliKelvin deep magnetic trap. The loading scheme allows one to increase the phase-space density of trapped molecules by accumulating packets from consecutive deceleration cycles in the trap. In the present experiment, accumulation of six packets is demonstrated to result in an overall increase of only slightly over a factor of two, limited by the trap-loss and reloading rates.

Superfluid and dissipative dynamics of a Bose-Einstein condensate in a periodic optical potential.

We create Bose-Einstein condensates of 87Rb in a static magnetic trap with a superimposed blue-detuned 1D optical lattice. By displacing the magnetic trap center we are able to control the condensate evolution. We observe a change in the frequency of the center-of-mass oscillation in the harmonic trapping potential, in analogy with an increase in effective mass. For fluid velocities greater than a local speed of sound, we observe the onset of dissipative processes up to full removal of the superfluid component. A parallel simulation study visualizes the dynamics of the Bose-Einstein condensate and accounts for the main features of the observed behavior.

Dipolar decay in two recent Bose-Einstein condensation experiments.

After the recent breakthrough to Bose-Einstein condensation ~BEC! in dilute ultracold atomic gases of Li, Na, and Rb @1–3#, it has become a priority to try to understand the finite lifetime of the trapped gas sample, in particular below the transition temperature. Since the mechanism of the decay is not yet completely clarified, it is useful to consider the theoretical predictions for the various possible partial decayrate constants. In this paper we present the decay-rate constants for the dipolar decay of the hyperfine states involved. For the case of Li that result has been given in a previous paper @4#. The dipolar decay-rate constants for Na and Rb will be considered here. In Fig. 1 we show the groundstate hyperfine structure for Na, Rb, and Rb as a function of magnetic field. In the following we refer to each of the hyperfine states in terms of the ~lower-case! single-atom quantum numbers f ,mf , although f is a good quantum number only for B50. Capital quantum numbers F ,MF are reserved for two-atom states involved in collisions. Instead of the doubly polarized f ,mf52,12 state in Na that we studied previously @4#, we will concentrate here on the 1,21 state for which BEC was realized experimentally @3#. As Fig. 1 shows, special significance has to be attributed to the field range up to 316 G in which the 1,21 state can be trapped in a static magnetic trap as a low-field seeking state. Also in the case of Rb we will concentrate on the dipolar decay of the state involved in the recent BEC experiment @1#, the doubly polarized 2,12 state. For completeness we will give the analogous result also for the isotope Rb. The method used has been sketched in Ref. @5#. Decay channels considered are all exothermal two-body decay channels not forbidden by selection rules, i.e., all are available combinations of lowerenergy f 1mf 1, f 2mf 2 combinations with MF5mf 11mf 2 at

A hybrid microwave-static magnetic trap for spin-polarized hydrogen

One approach to Bose condensing spin-polarized atomic hydrogen is to isolate the atoms from walls by using an electromagnetic trap. The most promising trap for this purpose is the microwave trap. Until now there has been no realistic means of loading this shallow potential trap. In this article we show that this can be achieved by combining a microwave trap with a static magnetic trap. This should enable the attainment of high densities and low temperatures required for BEC.

Evaporative cooling of spin-polarized atomic hydrogen.

A gas of hydrogen atoms, confined in a static magnetic trap, has been evaporatively cooled to temperatures of a few millikelvin. The initial trap configuration held the gas at 38 mK for as long as 5 h. Evaporative cooling reduced the temperature to 3.0 mK while maintaining the central density at 7.6\ifmmode\times\else\texttimes\fi{}${10}^{12}$ ${\mathrm{cm}}^{\ensuremath{-}3}$. These values were determined by measurement of the rate of electronic spin relaxation and are in agreement with model calculations. Further cooling to 1 mK (inferred from the model) has been achieved. Measurements were made of the efficiency of the evaporative cooling process.

Magnetic trapping of spin-polarized atomic hydrogen.

We have confined over 5\ifmmode\times\else\texttimes\fi{}${10}^{12}$ atoms of hydrogen in a static magnetic trap. The atoms are loaded into the trap by precooling with a dilution refrigerator. At operating densities near 1\ifmmode\times\else\texttimes\fi{}${10}^{13}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ the gas is observed to be electron and nuclear polarized in the uppermost hyperfine state. The long lifetime of the trapped gas (over 20 min) suggests that it is thermally decoupled from the wall and has evaporatively cooled to a temperature of about 40 mK. The residual decay of the gas density is consistent with spin relaxation induced by dipolar interactions between atoms.

Magnetic Trapping of Spin-Polarized Atomic Hydrogen

We have confined over 5×1012 atoms of hydrogen in a static magnetic trap. The atoms are loaded into the trap by precooling with a dilution refrigerator. At operating densities near 1×1013 cm-3 the gas is observed to be electron- and nuclear-polarized in the uppermost hyperfine state. The long lifetime of the trapped gas (over 20 minutes) suggests that it is thermally decoupled from the wall and has evaporatively cooled to a temperature of about 41 mK. The residual decay of the gas density is consistent with spin relaxation induced by dipolar interactions between atoms.

Evaporative cooling of magnetically trapped and compressed spin-polarized hydrogen.

A gas of spin-polarized atomic hydrogen can be prepared in the upper hyperfine states and loaded into a static magnetic trap. Evaporative cooling and magnetic compression of such a gas can produce temperatures of 30 \ensuremath{\mu}K and densities of ${10}^{14}$ ${\mathrm{cm}}^{\ensuremath{-}3}$. Under these conditions a Bose-Einstein condensate may form.