Preparation and determination of spin-polarized states in multi-Zeeman-sublevel atoms

Abstract

We demonstrate a simple technique to prepare and determine the desired internal quantum states in multi-Zeeman-sublevel atoms. By choosing appropriate coupling and pumping laser beams, atoms can be easily prepared in a desired Zeeman sublevel with high purity or in any chosen ground-state population distributions. The population distributions or state purities of such prepared atomic states can be determined by using a weak, circularlypolarized probe beam due to differences in transition strengths among different Zeeman sublevels. Preparing well-defined internal quantum states in multi-Zeeman-sublevel atoms (or spin-polarized quantum-state engineering) will be very important in demonstrating many interesting effects in quantum information processing with multi-level atomic systems.PACS numbers: 42.50.Gy, 32.80.Pj, 03.65.Wj 1 Preparing atoms into one specified internal quantum state and determining the population distribution in multi-Zeeman-sublevel atomic systems are very important in studying atom-field interactions, especially interesting schemes for quantum information processing such as light storage [1], quantum phase gate [2][3][4][5], and entanglement between atomic assemble and photons [6] or between a single trapped ion and a single photon [7].Demonstrations of these novel effects require more than two atomic energy levels and welldefined initial internal quantum state for the atoms, which can not be accomplished by simple optical pumping as in the case for a two-level atomic system. Although in most cases interesting effects can be experimentally demonstrated by simply considering degenerate Zeeman levels, so no specific ground-state population preparations are needed (as in the cases of electromagnetically induced transparency (EIT) [8-10] and photon storage [11]), there are many effects that demand better quantum-state preparation and determination in the multi-Zeeman-sublevel atomic systems. For example, in order to demonstrate quantum phase gate in multi-level atomic systems, such as the five-level M-type [3] and five-level combined M and tripod-type [5] systems, initial ground-state populations have to be prepared in specific Zeeman sublevels. Other examples include synthesis of arbitrary quantum states [12] and many other multi-level atomic systems for quantum information processing. Although specific atomic ground states were prepared in some of the previous experiments and the population distributions were estimated [6], no simple optical techniques have been developed, to the best of our knowledge, to determine the ground-state populations of the prepared internal quantum states of the atoms. Such measurements are very important in determining the coherent time of the photon storage [13], achieving large entanglement between photons and the atomic assemble [6], and realizing quantum phase gates due to cross-phase

Magneto-optical spectroscopy with polarization-modulated light

“…Finally polarization modulation with variable duty cycle can also find applications in the preparation and manipulation of specific atomic states, i.e., in metrology [18] and in quantum information processing [19].…”

Precision measurement of the nuclear polarization in laser-cooled, optically pumped37K

“…Although this population can be made quite small, the precision measurement described here requires knowledge of its distribution. There have been methods developed to probe this directly [21][22][23], but the specific constraints of our experiment, including the relatively low number of trapped atoms, make these impractical. Additionally, the polarization measurement must be non-destructive, preserving the polarization of the atoms in order to observe the β-asymmetry in the nuclear decay of the same atoms.…”

Quantum storage of optical signals and coherent manipulation of quantum states based on electromagnetically induced transparency

“…where sin g le , F=1, m=+1 state [31]. The experimentally prepared tripod system can be described well using the simple energy diagram shown in Figure 6(a), and the configurations of the writing, reading, and signal beams are shown in Figure 6(b), with all of the beams split from a single high-power diode laser.…”