Ultracold atom magnetic field microscopy enables the probing of current flow patterns in planar structures with unprecedented sensitivity. In polycrystalline metal (gold) films we observe longrange correlations forming organized patterns oriented at ±45• relative to the mean current flow, even at room temperature and at length scales orders of magnitude larger than the diffusion length or the grain size. 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. This indicates that ultracold atom magnetometry enables new insight into the interplay between disorder and transport.Thin metal films are the classic environment for studying the effect of geometric constraints [1,2] and crystal defects [3,4] on the transport of electrons. In a perfectly straight long wire that is free from structural defects, a direct current (DC) strictly follows the wire direction and creates a magnetic field in the plane perpendicular to the wire. An obstacle may locally change the direction of the current and consequently locally rotate the magnetic field close to the wire by an angle β in a plane parallel to the plane of the thin film wire.Ultracold atom magnetometry [5,6] on atom chips [7,8,9] allows for the sensitive probing of this angle β (and its spatial variation) with µrad (µm) resolution. Compared to scanning probes having a µm scale spatial resolution and 10 −5 T sensitivity, or superconducting quantum interference devices (SQUIDs) having 10 −13 T sensitivity but a resolution of tens of µm, ultracold atom magnetometry has both high sensitivity (10 −10 T) and high resolution (several µm) [6]. In addition, ultracold atoms enable high resolution over a large length scale (mm) in a single shot. This enables the simultaneous observations of microscopic and macroscopic phenomena, as described in this work.Using cold atoms just above the transition to BoseEinstein Condensation (BEC), we apply ultracold atom magnetometry to study the current deflection in three different precision-fabricated polycrystalline gold wires with a rectangular cross section of 200µm width and different thicknesses and crystalline grain sizes, as summarized in Table I [10]. Choosing the wire length along x, its width along y and thickness along z, Fig. 1 shows the maps of the angular variations β(x, y, z 0 ) = δB x (x, y, z 0 )/B y of the magnetic field created by a current of 180 mA flowing along the wire, measured at z 0 =3.5µm above its center (far from the edges).Even though at ambient temperature scattering by lattice vibrations (phonons) quickly diffuses the electronic motion, long-range correlations (tens of µm) in the current flow patterns can be seen. This is surprising as effects of static defects are usually observed only on a Table I. These fluctuations are...

ESR-STM is an emerging technique which is capable of detecting the precession of a single spin. We discuss the mechanism of ESR-STM based on a direct exchange coupling between the tunneling electrons and the local precessing spin S. We claim that since the number of tunneling electrons in a single precessing period is small (∼ 20) one may expect a net temporary polarization within this period that will couple via exchange interaction to the localized spin. This coupling will randomly modulate the tunneling barrier and create a dispersion in the tunneling current which is a product of a Larmor frequency component due to the precession of the single spin and the dispersion of the spin of the tunneling electrons. This noise component is spread over the whole frequency range for random white noise spin polarization of electrons. In opposite case the power spectrum of the spins of the tunneling electrons has a peak at zero frequency an elevated noise in the current at ωL will appear. We discuss the possible source of this spin polarization. We find that for relevant values of parameters signal to noise ratio in the spectral characteristic is 2-4 and is comparable to the reported signal to noise ratio [1,2]. The magnitude of the current fluctuation is a relatively weak increaing function of the DC current and the magnetic field. The linewidth produced by the back action effect of tunneling electrons on the precessing spin is also discussed.There is a growing realization that the technique of ESR-STM is capable of detecting the precession of a single surface spin by modulating the tunneling current at the Larmor frequency. This technique was successful in measuring Larmor frequency modulations in defects in semiconductor surfaces [1] and in paramagnetic molecules [2]. The increasing interest in this technique is due to the possibility to detect and manipulate a single spin [3].The alternative technique that allows one to detect single spin is the optically detected magnetic resonance (ODMR) spectroscopy in a single molecule [5]. In comparison, ESR-STM has the unique ability to correlate the spectroscopic information with the spatial information, detected at the atomic level. It also allows one to manipulate the position of the spin centers at the atomic level [4].There has been several proposals for the mechanism of detection. One is a polarization of the mobile carriers through spin orbit coupling, and modulation of the LDOS as a result of the precession [6]. Another one is the interference between two resonant tunneling components through the magnetic field splitted Zeeman levels [7]. Both of these mechanisms rely on a spin orbit coupling to couple a local spin S to the conduction electrons and have assumed no spin polarization of tunneling electrons. Recently however, Durkan and Welland [2] observed a strong signal in a system with a substantially smaller spin orbit coupling than what was assumed in the calculations [6], [7]. Motivated by these experiments we addressed a question: what is the role of the direct excha...

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 on the order of the deBroglie 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.