Amplifying single impurities immersed in a gas of ultra cold atoms

We present a method for amplifying a single or scattered impurities immersed in a background gas of ultra cold atoms so that they can be optically imaged and spatially resolved. Our approach relies on a Raman transfer between two stable atomic hyperfine states that is conditioned on the presence of an impurity atom. The amplification is based on the strong interaction among atoms excited to Rydberg states. We perform a detailed analytical study of the performance of the proposed scheme with particular emphasis on the influence of many-body effects.Comment: 5 pages, 4 figure

Disorder Potentials near Lithographically Fabricated Atom Chips

We show that previously observed large disorder potentials in magnetic microtraps for neutral atoms are reduced by about two orders of magnitude when using atom chips with lithographically fabricated high quality gold layers. Using one dimensional Bose-Einstein condensates, we probe the remaining magnetic field variations at surface distances down to a few microns. Measurements on a 100 um wide wire imply that residual variations of the current flow result from local properties of the wire.Comment: submitted on September 24th, 200

Ultracold atoms in radio-frequency-dressed potentials beyond the rotating wave approximation

We study dressed Bose-Einstein condensates in an atom chip radio-frequency trap. We show that in this system sufficiently strong dressing can be achieved to cause the widely used rotating wave approximation (RWA) to break down. We present a full calculation of the atom - field coupling which shows that the non-RWA contributions quantitatively alter the shape of the emerging dressed adiabatic potentials. The non-RWA contributions furthermore lead to additional allowed transitions between dressed levels. We use RF spectroscopy of Bose-Einstein condensates trapped in the dressed state potentials to directly observe the transition from the RWA to the beyond-RWA regime.Comment: 6 pages, 4 figure

Coupling a single electron to a Bose-Einstein condensate

The coupling of electrons to matter is at the heart of our understanding of material properties such as electrical conductivity. One of the most intriguing effects is that electron-phonon coupling can lead to the formation of a Cooper pair out of two repelling electrons, the basis for BCS superconductivity. Here we study the interaction of a single localized electron with a Bose-Einstein condensate (BEC) and show that it can excite phonons and eventually set the whole condensate into a collective oscillation. We find that the coupling is surprisingly strong as compared to ionic impurities due to the more favorable mass ratio. The electron is held in place by a single charged ionic core forming a Rydberg bound state. This Rydberg electron is described by a wavefunction extending to a size comparable to the dimensions of the BEC, namely up to 8 micrometers. In such a state, corresponding to a principal quantum number of n=202, the Rydberg electron is interacting with several tens of thousands of condensed atoms contained within its orbit. We observe surprisingly long lifetimes and finite size effects due to the electron exploring the wings of the BEC. Based on our results we anticipate future experiments on electron wavefunction imaging, investigation of phonon mediated coupling of single electrons, and applications in quantum optics.Comment: 4 pages, 3 figures and supplementary informatio

Non-equilibrium coherence dynamics in one-dimensional Bose gases

Low-dimensional systems are beautiful examples of many-body quantum physics. For one-dimensional systems the Luttinger liquid approach provides insight into universal properties. Much is known of the equilibrium state, both in the weakly and strongly interacting regime. However, it remains a challenge to probe the dynamics by which this equilibrium state is reached. Here we present a direct experimental study of the coherence dynamics in both isolated and coupled degenerate 1d Bose gases. Dynamic splitting is used to create two 1d systems in a phase coherent state. The time evolution of the coherence is revealed in local phase shifts of the subsequently observed interference patterns. Completely isolated 1d Bose gases are observed to exhibit a universal sub-exponential coherence decay in excellent agreement with recent predictions by Burkov et al. [Phys. Rev. Lett. 98, 200404 (2007)]. For two coupled 1d Bose gases the coherence factor is observed to approach a non-zero equilibrium value as predicted by a Bogoliubov approach. This coupled-system decay to finite coherence is the matter wave equivalent of phase locking two lasers by injection. The non-equilibrium dynamics of superfluids plays an important role in a wide range of physical systems, such as superconductors, quantum-Hall systems, superfluid Helium, and spin systems. Our experiments studying coherence dynamics show that 1d Bose gases are ideally suited for investigating this class of phenomena.Comment: to appear in natur

Highly versatile atomic micro traps generated by multifrequency magnetic field modulation

We propose the realization of custom-designed adiabatic potentials for cold atoms based on multimode radio frequency radiation in combination with static inhomogeneous magnetic fields. For example, the use of radio frequency combs gives rise to periodic potentials acting as gratings for cold atoms. In strong magnetic field gradients the lattice constant can be well below 1 micrometer. By changing the frequencies of the comb in time the gratings can easily be propagated in space, which may prove useful for Bragg scattering atomic matter waves. Furthermore, almost arbitrarily shaped potential are possible such as disordered potentials on a scale of several 100 nm or lattices with a spatially varying lattice constant. The potentials can be made state selective and, in the case of atomic mixtures, also species selective. This opens new perspectives for generating tailored quantum systems based on ultra cold single atoms or degenerate atomic and molecular quantum gases.Comment: 12 pages, 6 figure