BASES PARA UNA LECTURA EFICAZ

external magnetic field fluctuations. The Feshbach magnetic field strength is ramped from 3.2 G to 20.3 G within 10 ms. After a short settling time for the magnetic field the Zeeman states are transferred from _|3/2,3/2_i to _|1/2,1/2_i for6Li and _|9/2,9/2_i to

|9/2,₋9/2_i for 40_{K. The external field causes a hyperfine splitting of the ground state}

what allows to sensitively address only one single Zeeman state. The frequency for the

6_{Li Zeeman state transfer is swept from 270.016 MHz to 269.392 MHz within 735µs. This}

duration allows to transfer all atoms to the desired final Zeeman state_|1/2,1/2_i of 6_Li.

The comparatively large Rabi frequency of Ω = 2π_×30(2) kHz based on a high power radiofrequency source admits to perform the transfer relatively fast.

After the state preparation of 6Li, the transfer frequency of 40K is swept from 7.088 MHz to 5.775 MHz within 336µs. The Rabi frequency for this transition is Ω = 2π_×18.3(1.4) kHz. The duration of the sweep is long enough to transfer all 40_{K atoms}

to the state_|9/2,₋9/2_i, and no dephasing during the transfer occurs since the duration is sufficiently smaller than the mean trapping oscillation period or the mean time be- tween collisions. In a second ARP the 40_{K atoms are finally transferred from the state}

|9/2,₋9/2_i to _|9/2,₋5/2_i. This second ARP is done after a magnetic field sweep from 20.3 G to 156.90 G, and at a magnetic field strength on the atomic side of the Feshbach resonance at 155 G in order to circumvent molecule formation. There is a nearby second Feshbach resonance around 163 G, which involves the same Zeeman states of6_{Li and}40_K

(Willeet al., 2008). The transfer frequency is swept from 36.9943 MHz to 39.1513 MHz in 500µs. Depending on the specific measurement, the last state preparation for40K can be also accomplished optionally below the Feshbach resonance position on the molecular side of the resonance at 152.40 G. The frequency in this case is swept from 36.2292 MHz to 38.3241 MHz in 500µs.

For all ARP of 6Li and 40K a sweep duration of seven times the Rabi period is chosen. Due to stability reasons, 6Li is transferred first to the absolute ground state of the hyperfine manifold before the ARP’s for40_{K are accomplished.}

5.2

Feshbach loss spectroscopy

As depicted in Tab. 2.1, severals-wave interspecies Feshbach resonances are identified in (Willeet al., 2008) by Feshbach loss spectroscopy of a non-degenerate 6_Li-40_{K mixture.}

In the following, the interspecies Feshbach resonance at 155 G is characterized. This specific resonance possesses a comparatively large width of 0.81 G according to coupled channels calculations (Wille et al., 2008), and involves the states _|1/2,1/2_i of 6_{Li and}

|9/2,₋5/2_i of 40K. Some preparatory measurements are also done at the interspecies Feshbach resonance located at 168 G, since this resonance implies a simpler state prepa- ration6_{Li|1/2,1/2iand} 40_{K|9/2,−9/2i, but the width is considerably smaller.}

In this section, the lifetime of a 6Li-40K mixture close to the interspecies Feshbach resonance at 155 G is investigated. The mixture is loaded into the ODT with trapping frequencies given in Eq. (5.1). In this trap particle numbers of NLi ≈ NK ≈ 1×105

and temperatures of TLi = 0.4TFLi and TK = 0.6TFK (TF being the Fermi temperature)

154.6 154.7 154.8 1 10 100 1000 6 Li 40 K L i f e t i m e ( m s) Magnetic field B hold (G) B i T hold B hold B time B 0

Figure 5.2: Lifetime of the6_Li-40_{K mixture as a function of magnetic field in the vicinity}

of an interspecies Feshbach resonance. The lifetime of the mixture can be varied by two orders of magnitude. The minimum lifetime is found to be located at a magnetic field strength ofB = 154.72(5) G.

After preparation of the mixture in the absolute ground states, the magnetic bias field is ramped in 30 ms from 20.3 G to Bi = 152.40 G, i.e. to the molecular side of the

Feshbach resonance. The 40K atoms are then transferred to the state _|9/2,₋5/2_i by an ARP. Subsequently, the magnetic field is ramped from Bi to a variable value Bhold

within 0.5 ms where the lifetime of the mixture is investigated by holding the atoms for a variable timeTholdat constant magnetic field strengthBhold. After the holding period,

the magnetic field strength is rapidly decreased with an initial slope of 820 G/ms to a bias field of 1 G. After a subsequent holding time of 5 ms, the clouds are released from the trap, and the 6Li and 40K atoms are imaged by resonant light after 1 ms and 4 ms of free expansion. The data is presented in Fig. 5.2. Each data point corresponds to a fitted time constant τ of the exponential decay of the atom numbers of 6_{Li and} 40_K

at a single magnetic field strength. The lifetime of the mixture τ decreases close to the resonance position by two orders of magnitude to a minimum value of only 10 ms. The corresponding magnetic field strength of the minimum is B = 154.72(5) G. This determined magnetic field position of the maximum loss will be discussed and compared to forthcoming measurements in Sec. 6.4.

The asymmetric lineshape of the losses is in qualitative agreement with predictions from three-body relaxation (D’Incao and Esry, 2006; Levinsen and Petrov, 2011). This

5.3 Heteronuclear Fermi-Fermi molecules