An atom interferometer offers means to measure physical constants and physical quantities with a high precision, with relatively low cost and convenience as a table-top experiment. A precision measurement of a gravitational acceleration can test fundamental physics concepts such as Einstein equivalence principle (EEP). We identified that the two lithium isotopes (
7Li and
6Li) have an advantage for the test of EEP, according to the standard model extension (SME). We aim to build the world's first lithium atom interferometer and test the Einstein equivalence principle.\\\\We demonstrate a new laser cooling method suitable for a lithium atom interferometer. Although lithium is often used in ultra-cold atom experiments for its interesting physical properties and measurement feasibility, it is more difficult to laser cool lithium than other alkali atoms due to its unresolved hyperfine states, light mass (large recoil velocity) and high temperature from the oven. Typically, standard laser cooling techniques such as Zeeman slowers and magneto-optical traps are used to cool lithium atoms to about 1 mK, and the evaporative cooling method is used to cool lithium atoms to a few
muK for Bose-Einstein condensate (BEC) experiments. However, for the atom interferometry purpose, the evaporative cooling method is not ideal for several reasons: First, its cooling efficiency is so low (0.01 \\% or less) that typically only
104−105 atoms are left after cooling when one begins with
109 atoms. More atoms in an atom interferometer are needed to have a better signal to noise ratio. Second, an evaporative cooling is used to make a BEC, but we do not need a BEC to make an atom interferometer. In an atom interferometer, a high density of atoms as in a BEC should be avoided since it causes a phase shift due to atom interactions. Third, a setup for an evaporative cooling requires intricate RF generating coils or a high power laser. \\\\With a simple optical lattice and a moderate laser power (100 mW), we achieved a sub-Doppler cooling of lithium by a new laser cooling method despite the fact that lithium has un-resolved hyperfine structure. We identified that the Sisyphus cooling and the adiabatic cooling mechanisms cooperate and give both lower temperature and higher cooling efficiency than the result that can be achieved by each alone. We cooled
7Li atoms to
sim;50;muK (about 8 times the recoil temperature) in a one dimensional lattice with cooling efficiency of
50. In three dimensions the cooling temperature was limited to
90,muK due to instability of our 3D lattice, however the same principle applies and potentially a lower temperature can be achieved in 3D as well.
Lithium is an important element in atomic quantum gas experiments because its interactions are highly tunable due to broad Feshbach resonances and zero-crossings and because it has two stable isotopes: 6Li, a fermion, and 7Li, a boson. Although lithium has special value for these reasons, it also presents experimental challenges. In this article, we review some of the methods that have been developed or adapted to confront these challenges, including beam and vapor sources, Zeeman slowers, sub-Doppler laser cooling, laser sources at 671 nm, and all-optical methods for trapping and cooling. Additionally, we provide spectral diagrams of both 6Li and 7Li and present plots of Feshbach resonances for both isotopes.
The authors have succeeded in demonstrating laser isotope enrichment via magnetic deflection of a polarized atomic beam. By using a single dye laser with the frequency tuned to the two accidentally close transitions of the natural lithium (2 2 S 1/2 (F=1/2) to 2 2 P 3/2 for 6 Li and 2 2 S 1/2 (F=2) to 2 2 P 1 2/(F=1) for 7 Li), 6 Li and 7 Li atoms in a beam were positively and negatively polarized respectively. The 6 Li enrichment was achieved via magnetic deflection of the polarized beam through a hexapole magnet which focuses the positively polarized 6 Li atoms and defocuses the negatively polarized 7 Li atoms. The dependence of 7 Li polarization on laser intensity was experimentally examined, and the result was in good agreement with that calculated by rate equations. The abundance ratio of 6 Li to 7 Li was enhanced from 1 : 12.5 to about 1 : 3.1.
We generate an atomic beam of titanium (Ti) using a "Ti-ball" Ti-sublimation pump, which is a common getter pump used in ultrahigh vacuum systems. We show that the sublimated atomic beam can be optically pumped into the metastable 3d3(4F)4s a5F5 state, which is the lower energy level in a cycling optical transition that can be used for laser cooling. We measure the atomic density and transverse and longitudinal velocity distributions of the beam through laser fluorescence spectroscopy. We find a metastable atomic flux density of 4.3(2) × 109 s-1 cm-2 with a mean forward velocity of 773(8) m/s at 2.55 cm directly downstream of the center of the Ti-ball. Owing to the details of optical pumping, the beam is highly collimated along the transverse axis parallel to the optical pumping beam and the flux density falls off as 1/r. We discuss how this source can be used to load atoms into a magneto-optical trap.
Ion sources based on laser cooling have recently provided new pathways to high-resolution microscopy, ion milling, and ion implantation. Here, we present the design and detailed characterization of a 7Li magneto-optical trap ion source (MOTIS) with a peak brightness of (1.2 ± 0.2) × 105 A m-2 sr-1 eV-1 and a maximum continuous current over 1 nA. These values significantly surpass previous Li MOTIS performance benchmarks. Using simple models, we discuss how the performance of this system relates to fundamental operating limits. This source will support a range of projects using lithium ion beams for surface microscopy and nanostructure characterization, including Li+ implantation for studies of ionic transport in energy storage materials.
The purpose of our collaboration is to study ultracold collisions in a gas sample of atomic lithium. The associated experimental context is a scheme for producing such a gas sample in conditions where Bose-Einstein condensation (BEC) should be observable in the case of the {sup 7}Li isotope or Fermi degenerate behavior for the {sup 6}Li isotope. The plan is to load 10{sup 5}-10{sup 9} Li atoms from a laser cooled atomic beam into a magnetic trap with a diameter of about 1 mm. The fundamental limitation to achieving high density will be collisions of ground state atoms. We are interested in the loss of atomic density in a magnetic trap due to two-body dipolar collisions and spin-exchange collisions. Lithium atoms offer important advantages relative to other alkali atoms from the theoretical point of view. In the first place there is the greater accuracy of the available long-range potential parameters. Secondly, one avoids a complication of the heavier alkalis connected with the unknown spin-spin term following in second order from the electronic spin-orbit couplings In this contribution we present preliminary results for the above loss-mechanisms.