Guiding Neutral Atoms with a Wire

Atom optics with microfabricated optical elements

Atom optics, guided atoms, and atom interferometry

A large variety of trapping and guiding potentials can be designed by bringing cold atoms close to charged or current carrying material objects. We describe the basic principles of constructing microscopic traps and guides and how to load atoms into them. The simplicity and versatility of these methods will allow for miniaturization and integration of atom optical elements into matter-wave quantum circuits on Atom Chips. These could form the basis for robust and widespread applications in atom optics, ranging from fundamental studies in mesoscopic physics to possibly quantum information systems.

An array of square current-carrying wires is proposed to construct a two-dimensional (2D) array of surface magneto-optical traps and Ioffe magnetic ones for realizing a 2D lattice of Bose-Einstein condensations (BECs) on an atom chip. Our study shows that when a vertical homogeneous bias magnetic field is only used, the wires will form a 2D array of quadrupole magnetic traps, which can be used to construct 2D lattice of surface magneto-optical micro-traps. While another horizontal homogeneous bias field is added simultaneously, the above 2D array of quadrupole micro-traps will be changed as an array of surface Ioffe micro-traps, which can be used to form a 2D magnetic lattice and then realize a 2D array of BECs. The dynamic loading process of cold (87)Rb atoms from each micro-MOT into Ioffe micro-trap is studied by using Monte-Carlo simulations, and our results show that the scheme can be used to realize a natural and effective loading of cold atoms from 2D array of micro-MOTs into 2D array of Ioffe micro-traps, and the loading efficiency can be reach ~ 65%. Moreover, the positions of each BEC (or MOT) in 2D array of magnetic micro-traps can be controlled by adjusting the currents in the wires or by changing the additional vertical bias field.

Recent developments in atom optics have led to different approaches to lithographic techniques with neutral atoms. One of these is the use of diffraction from free-standing masks, which is sometimes called atom holography. There, narrow structures arise due to matter-wave interference in the Fresnel regime. In the presented experiment, we demonstrate that the wave nature of atoms can be used to produce periodic structures with small periodicities. We used the Talbot effect in the Fresnel diffraction regime behind a microfabricated transmission grating. The Talbot effect is the self-imaging of a grating of periodicity d illuminated with plane coherent waves.

Magnetic trapping of laser-cooled neutral atoms has been demonstrated at NBS and is progressing in other laboratories. Confinement of any object requires exchanging kinetic for potential energy, and for neutral atoms, this necessarily derives from shifts of internal energy levels. This is implemented through the force experienced by the atomic magnetic moment in a carefully designed, highly inhomogeneous field. Since magnetic fields of convenient strength can shift atomic energy levels by only a few gigahertz (temperature ≌ 0.1 K), neutral atom traps are very shallow and must be loaded with very cold atoms. We present some motivations for using magnetic traps and then discuss the constraints and optimal configurations of various arrangements. For example, no trap can be isotropic. Next we discuss both the classical and quantum mechanical motions of trapped atoms. These motions are important for at least two reasons: First, several schemes under study for further cooling depend on knowing the position and velocity of the atoms, as well as the vector field at each point along the orbit. Second, magnetic traps depend on the atomic moment remaining aligned with the field as the atom orbits in the trap, and this precludes rapid motion through a low-field region.

We describe the basic principles of quantum information processing with cold neutral atoms on an atom chip.

Mercury is the heaviest stable atom that could be laser cooled, and have a large nuclear charge number. So it has a distinct advantage in quantum precision measurement such as fine-structure constant α and permanent electric dipole moment. Due to its insensitivity of black body radiation, atomic mercury is a good candidate of optical clock. Here we report our recent development of laser cooling of neutral mercury atom. By cooling the mercury source to about -70°C, an ultra-high vacuum system was realized to produce ultracold mercury atoms. The commercial frequency quadrupled semiconductor laser is locked on the cooling transition ( 1 S 0 - 3 P 1 transition, wavelength of 253.7 nm) by sub-Doppler frequency modulation spectroscopy. By the modification with feed-forward method, the UV laser becomes faster tunable and more stable. A folded beam configuration was used to realize the magneto-optical trap (MOT) because of the shortage of cooling laser power, and the ultracold mercury atoms were observed by fluorescence detection. All of six rich abundant isotopes have been observed, and the atom number is about 1.5×10 6 with density of 3.5×10 9 /cm 3 for 202 Hg. With optical shutter and the programmable system to control the time sequence, the temperature of ultracold atoms can be measured by time of flight method. To enhance the laser power, a 1014.8 nm fiber laser amplifier was developed, which can work at room temperature. After two stages of frequency doubling, about 75 mW of 253.7 nm UV laser were generated, and the saturated absorption spectroscopy of mercury atom was also observed. More power of UV laser could help to trap more atoms in the future. These works laid a good foundation to realize the mercury lattice clock.

A Fourier optics approach can be a concise and powerful tool to solve problems in atom optics. In this report, we adopt it to investigate the kinetic behavior of cold atoms passing through a far red-detuned Gaussian beam. We demonstrate that the aberration has significant influence on the evolution of the atomic cloud, which is rooted in the deviation of the Gaussian profile from the quadratic form. In particular, we observe an intriguing effect analogous to Fresnel’s double prism with cold atoms. The experimental results are in good agreement with the numerical simulation.

A method for constrained optimisation of the design of a scanning helium microscope

This paper summarizes some important achievements of quantum information processing with trapped ions or neutral atoms. In particular, we describe the storage of information and realization of two-qubit gates with ions, as well as the creation of entanglement and quantum simulation with cold atoms in optical lattices.

Imagine you could produce an artificial crystal for quantum matter, defect free and with complete control over the periodic crystal potential. The shape of the periodic potential, its depth and the interactions between the underlying particles could be changed at will and the particles could be moved around in a highly controlled way, at essentially zero temperature. This sounds almost too good to be true, but it is in fact what optical lattices have made possible for cold and ultracold atoms.

Many proposals for quantum information processing require precise control over the motion of neutral atoms, as in the manipulation of coherent matter waves or the confinement and localization of individual atoms. Patterns of micron-sized wires, fabricated lithographically on a flat substrate, can conveniently produce large magnetic-field gradients and curvatures to trap cold atoms and to facilitate the production of Bose-Einstein condensates. The intent of this paper is to provide the researcher who has access to a standard clean-room enough information to design and fabricate such devices.

Precision laser spectroscopy at λ = 657 nm based on cold neutral Ca atoms released from a magneto-optical trap (MOT) is described. Systematic contributions to the uncertainty resulting from the residual velocity of the atoms and the acceleration in the gravitational field are determined and their influence is reduced by using a combination of different atom interferometers. The results are applied to an optical frequency standard based on Ca atoms. A fractional uncertainty in the measured clock frequency 2 • 10 -14 is observed. The application of a novel method for producing ultra-cold atoms showed in first atom interferometric measurements the potential to further reduce the uncertainty to below 10 -15 .

Electrostatic microtrap on the surface of the chip