Yonathan Japha

Long-range order in electronic transport through disordered metal films.

Ultracold atom magnetic field microscopy enables the probing of current flow patterns in planar structures with unprecedented sensitivity. In polycrystalline metal (gold) films, we observed long-range correlations forming organized patterns oriented at ±45° relative to the mean current flow, even at room temperature and at length scales larger than the diffusion length or the grain size by several orders of magnitude. The preference to form patterns at these angles is a direct consequence of universal scattering properties at defects. The observed amplitude of the current direction fluctuations scales inversely to that expected from the relative thickness variations, the grain size, and the defect concentration, all determined independently by standard methods. Ultracold atom magnetometry thus enables new insight into the interplay between disorder and transport.

Fifteen years of cold matter on the atom chip: promise, realizations, and prospects

Here we review the field of atom chips in the context of Bose–Einstein Condensates (BEC) as well as cold matter in general. Twenty years after the first realization of the BEC and 15 years after the realization of the atom chip, the latter has been found to enable extraordinary feats: from producing BECs at a rate of several per second, through the realization of matter-wave interferometry, and all the way to novel probing of surfaces and new forces. In addition, technological applications are also being intensively pursued. This review will describe these developments and more, including new ideas which have not yet been realized.

Nanowire atomchip traps for sub-micron atom–surface distances

We present an analysis of magnetic traps for ultracold atoms based on current-carrying wires with sub-micron dimensions. We analyze the physical limitations of these conducting wires as well as how such miniaturized magnetic traps are affected by the nearby surface due to tunneling to the surface, surface thermal noise, electron scattering within the wire and the Casimir?Polder force. We show that wires with cross sections as small as a few tens of nanometers should enable robust operating conditions for coherent atom optics (e.g. tunneling barriers for interferometry). In particular, trap sizes of the order of the de Broglie wavelength become accessible, based solely on static magnetic fields, thereby bringing the atomchip a step closer to fulfilling its promise of a compact device for complex and accurate quantum optics with ultracold atoms.

Trapping cold atoms using surface-grown carbon nanotubes

We present a feasibility study for loading cold atomic clouds into magnetic traps created by singlewall carbon nanotubes grown directly onto dielectric surfaces. We show that atoms may be captured for experimentally sustainable nanotube currents, generating trapped clouds whose densities and lifetimes are sufficient to enable detection by simple imaging methods. This opens the way for a novel type of conductor to be used in atomchips, enabling atom trapping at sub-micron distances, with implications for both fundamental studies and for technological applications.

Simultaneous optical trapping and detection of atoms by microdisk resonators

We propose a scheme for simultaneously trapping and detecting single atoms near the surface of a substrate using whispering gallery modes of a microdisk resonator. For efficient atom-mode coupling, the atom should be placed within approximately 150nm from the disk. We show that a combination of red and blue detuned modes can form an optical trap at such distances while the backaction of the atom on the field modes can simultaneously be used for atom detection. We investigate these trapping potentials including van-der-Waals and Casimir-Polder forces and discuss corresponding atom detection efficiencies, depending on a variety of system parameters. Finally, we analyze the feasibility of nondestructive detection.

A self-interfering clock as a “which path” witness

Interfering with time The interference pattern arising from light or particles passing through a double slit is a simple experiment that belies the subtleties of interpretation when attempting to describe and understand the effect. For example, determining “which path” the light or particles travel can result in the interference pattern disappearing. Margalit et al. present a new take on interferometry using time (see the Perspective by Arndt and Brand). A clock—i.e., the internal state of a cold atom condensate—was coherently split and brought back together to interfere. Making one-half of the clock tick at a different rate resulted in a change in the interference pattern, possibly as a consequence of the time being a “which path” witness. Science, this issue p. 1205; see also p. 1168 A cloud of cold rubidium atoms is used to demonstrate clock interferometry. [Also see Perspective by Arndt and Brand] In Einstein’s general theory of relativity, time depends locally on gravity; in standard quantum theory, time is global—all clocks “tick” uniformly. We demonstrate a new tool for investigating time in the overlap of these two theories: a self-interfering clock, comprising two atomic spin states. We prepare the clock in a spatial superposition of quantum wave packets, which evolve coherently along two paths into a stable interference pattern. If we make the clock wave packets “tick” at different rates, to simulate a gravitational time lag, the clock time along each path yields “which path” information, degrading the pattern’s visibility. In contrast, in standard interferometry, time cannot yield “which path” information. This proof-of-principle experiment may have implications for the study of time and general relativity and their impact on fundamental effects such as decoherence and the emergence of a classical world.

Using time-reversal symmetry for sensitive incoherent matter-wave Sagnac interferometry.

We present a theory of the transmission of guided matter-waves through Sagnac interferometers. Interferometer configurations with only one input and one output port have a property similar to the phase rigidity observed in the transmission through Aharonov-Bohm interferometers in coherent mesoscopic electronics. This property enables their operation with incoherent matter-wave sources. High rotation sensitivity is predicted for high finesse configurations.

Model for organized current patterns in disordered conductors

We present a general theory of current deviations in straight current-carrying wires with random imperfections, which quantitatively explains the recent observations of organized patterns of magnetic field corrugations above micrometer-scale evaporated wires. These patterns originate from the most efficient electron scattering by Fourier components of the wire imperfections with wavefronts along the 45° direction. We show that long-range effects of surface or bulk corrugations are suppressed for narrow wires or wires having an electrically anisotropic resistivity.

Magnetic interactions of cold atoms with anisotropic conductors

Abstract.We analyze atom-surface magnetic interactions on atom chips where the magnetic trapping potentials are produced by current carrying wires made of electrically anisotropic materials. We discuss a theory for time dependent fluctuations of the magnetic potential, arising from thermal noise originating from the surface. It is shown that using materials with a large electrical anisotropy results in a considerable reduction of heating and decoherence rates of ultra-cold atoms trapped near the surface, of up to several orders of magnitude. The trap loss rate due to spin flips is expected to be significantly reduced upon cooling the surface to low temperatures. In addition, the electrical anisotropy significantly suppresses the amplitude of static spatial potential corrugations due to current scattering within imperfect wires. Also the shape of the corrugation pattern depends on the electrical anisotropy: the preferred angle of the scattered current wave fronts can be varied over a wide range. Materials, fabrication, and experimental issues are discussed, and specific candidate materials are suggested.

Coherent Stern–Gerlach momentum splitting on an atom chip

In the Stern-Gerlach effect, a magnetic field gradient splits particles into spatially separated paths according to their spin projection. The idea of exploiting this effect for creating coherent momentum superpositions for matter-wave interferometry appeared shortly after its discovery, almost a century ago, but was judged to be far beyond practical reach. Here we demonstrate a viable version of this idea. Our scheme uses pulsed magnetic field gradients, generated by currents in an atom chip wire, and radio-frequency Rabi transitions between Zeeman sublevels. We transform an atomic Bose-Einstein condensate into a superposition of spatially separated propagating wavepackets and observe spatial interference fringes with a measurable phase repeatability. The method is versatile in its range of momentum transfer and the different available splitting geometries. These features make our method a good candidate for supporting a variety of future applications and fundamental studies.