Showing papers by "Jörg Schmiedmayer published in 2011"

Cavity QED with magnetically coupled collective spin states.

Abstract: We report strong coupling between an ensemble of nitrogen-vacancy center electron spins in diamond and a superconducting microwave coplanar waveguide resonator. The characteristic scaling of the collective coupling strength with the square root of the number of emitters is observed directly. Additionally, we measure hyperfine coupling to $^{13}\mathrm{C}$ nuclear spins, which is a first step towards a nuclear ensemble quantum memory. Using the dispersive shift of the cavity resonance frequency, we measure the relaxation time of the NV center at millikelvin temperatures in a nondestructive way.

Twin-atom beams

Abstract: Twin photons — pairs of highly correlated photons — are one of the building blocks for quantum optics, and are used in both fundamental tests of quantum physics and technological applications. Now an efficient source for correlated atom pairs is demonstrated, promising to enable a wide range of experiments in the field of quantum matter-wave optics.

The Dynamics and Prethermalization of One Dimensional Quantum Systems Probed Through the Full Distributions of Quantum Noise

Abstract: Quantum noise correlations have been employed in several areas of physics, including condensed matter, quantum optics and ultracold atoms, to reveal the non-classical states of the systems. To date, such analyses have mostly focused on systems in equilibrium. In this paper, we show that quantum noise is also a useful tool for characterizing and studying the non-equilibrium dynamics of a one-dimensional (1D) system. We consider the Ramsey sequence of 1D, two-component bosons, and obtain simple, analytical expressions for time evolutions of the full distribution functions for this strongly correlated, many-body system. The analysis can also be directly applied to the evolution of interference patterns between two 1D quasi-coindensates created from a single condensate through splitting. Using the tools developed in this paper, we demonstrate that 1D dynamics in these systems exhibits the phenomenon known as 'prethermalization', where the observables of non-equilibrium, long-time transient states become indistinguishable from those of thermal equilibrium states.

Two-point phase correlations of a one-dimensional bosonic Josephson junction.

Abstract: We realize a one-dimensional Josephson junction using quantum degenerate Bose gases in a tunable double well potential on an atom chip. Matter wave interferometry gives direct access to the relative phase field, which reflects the interplay of thermally driven fluctuations and phase locking due to tunneling. The thermal equilibrium state is characterized by probing the full statistical distribution function of the two-point phase correlation. Comparison to a stochastic model allows us to measure the coupling strength and temperature and hence a full characterization of the system.

Mach-Zehnder interferometry with interacting trapped Bose-Einstein condensates

Abstract: We theoretically analyze a Mach-Zehnder interferometer with trapped condensates and find that it is surprisingly stable against the nonlinearity induced by interparticle interactions. The phase sensitivity, which we study for number-squeezed input states, can overcome the shot noise limit and be increased up to the Heisenberg limit provided that a Bayesian or maximum-likelihood phase estimation strategy is used. We finally demonstrate the robustness of the Mach-Zehnder interferometer in the presence of interactions against condensate oscillations and a realistic atom-counting error.

Absorption imaging of ultracold atoms on atom chips.

Abstract: Imaging ultracold atomic gases close to surfaces is an important tool for the detailed analysis of experiments carried out using atom chips. We describe the critical factors that need be considered, especially when the imaging beam is purposely reflected from the surface. In particular we present methods to measure the atom-surface distance, which is a prerequisite for magnetic field imaging and studies of atom surface-interactions.

Absorption Imaging of Ultracold Atoms on Atom Chips

Abstract: Imaging ultracold atomic gases close to surfaces is an important tool for the detailed analysis of experiments carried out using atom chips. We describe the critical factors that need be considered, especially when the imaging beam is purposely reflected from the surface. In particular we present methods to measure the atom-surface distance, which is a prerequisite for magnetic field imaging and studies of atom surface-interactions.

The Shapiro effect in atomchip-based bosonic Josephson junctions

Abstract: We analyze the emergence of Shapiro resonances in tunnel- coupled Bose-Einstein condensates, realizing a bosonic Josephson junction Our analysis is based on an experimentally relevant implementation using magnetic double-well potentials on an atomchip In this configuration, the potential bias (implementing the junction voltage) and the potential barrier (realizing the Josephson link) are intrinsically coupled We show that the dynamically driven system exhibits significantly enhanced Shapiro resonances which will facilitate experimental observation To describe the system's response to the dynamic drive, we compare a single-mode Gross-Pitaevskii (GP) description, an improved two-mode (TM) model and the self-consistent multi-configurational time-dependent Hartree equations for bosons (MCTDHB) method We show that in the case of significant atom-atom interactions, the spatial dynamics of the involved modes has to be taken into account and only the MCTDHB method allows reliable predictions

Dephasing in coherently split quasicondensates

Abstract: We numerically model the evolution of a pair of coherently split quasicondensates. A truly one-dimensional case is assumed, so that the loss of the (initially high) coherence between the two quasicondensates is due to dephasing only, but not due to the violation of integrability and subsequent thermalization (which are excluded from the present model). We confirm the subexponential time evolution of the coherence between two quasicondensates $\ensuremath{\propto}\mathrm{exp}[\ensuremath{-}(t/{t}_{0}){}^{2/3}]$, experimentally observed by Hofferberth et al. [Nature 449, 324 (2007)]. The characteristic time ${t}_{0}$ is found to scale as the square of the ratio of the linear density of a quasicondensate to its temperature, and we analyze the full distribution function of the interference contrast and the decay of the phase correlation.

Controlling quantum information processing in hybrid systems on chips

Abstract: We investigate quantum information processing, transfer and storage in hybrid systems comprised of diverse blocks integrated on chips. Strong coupling between superconducting (SC) qubits and ensembles of ultracold atoms or NV-center spins is mediated by a microwave transmission-line resonator that interacts near-resonantly with the atoms or spins. Such hybrid devices allow us to benefit from the advantages of each block and compensate for their disadvantages. Specifically, the SC qubits can rapidly implement quantum logic gates, but are "noisy" (prone to decoherence), while collective states of the atomic or spin ensemble are "quiet"(protected from decoherence) and thus can be employed for storage of quantum information. To improve the overall performance (fidelity) of such devices we discuss dynamical control to optimize quantum state-transfer from a "noisy" qubit to the "quiet" storage ensemble. We propose to maximize the fidelity of transfer and storage in a spectrally inhomogeneous spin ensemble, by pre-selecting the optimal spectral portion of the ensemble. Significant improvements of the overall fidelity of hybrid devices are expected under realistic conditions. Experimental progress towards the realization of these schemes is discussed.

Interferometry with atoms

Abstract: Optics and interferometry with matter waves is the art of coherently manipulating the translational motion of particles like neutrons, atoms and molecules. Coherent atom optics is an extension of techniques that were developed for manipulating internal quantum states. Applying these ideas to translational motion required the development of techniques to localize atoms and transfer population coherently between distant localities. In this view position and momentum are (continuous) quantum mechanical degrees of freedom analogous to discrete internal quantum states. In our contribution we start with an introduction into matter wave optics in sect. 1, discuss coherent atom optics and atom interferometry techniques for molecular beams in sect. 2 and for trapped atoms in sect. 3. In sect. 4 we then describe tools and experiments that allow us to probe the evolution of quantum states of many-body systems by atom interference.

Single spontaneous photon as a coherent beamsplitter for an atomic matter-wave

Abstract: An atom recoils as it emits a photon. Researchers now show that the two possible recoil trajectories become coherently superimposed when a mirror is placed near the atom. This is because the mirror prevents the photon from giving away any information about the recoil direction.

The dynamics and prethermalization of one dimensional quantum systems probed through the full distributions of quantum noise

Abstract: Quantum noise correlations have been employed in several areas in physics including condensed matter, quantum optics and ultracold atom to reveal non-classical states of the systems. So far, such analysis mostly focused on systems in equilibrium. In this paper, we show that quantum noise is also a useful tool to characterize and study the non-equilibrium dynamics of one dimensional system. We consider the Ramsey sequence of one dimensional, two-component bosons, and obtain simple, analytical expressions of time evolutions of the full distribution functions for this strongly-correlated, many-body system. The analysis can also be directly applied to the evolution of interference patterns between two one dimensional quasi-condensates created from a single condensate through splitting. Using the tools developed in this paper, we demonstrate that one dimensional dynamics in these systems exhibits the phenomenon known as "prethermalization", where the observables of {\it non-equilibrium}, long-time transient states become indistinguishable from those of thermal {\it equilibrium} states.

Atom Chip Fabrication

Abstract: One of the key promises of atom chips is the building of a robust quantum laboratory by miniaturizing and integrating quantum optics and atomic physics tools on a single device, on a chip [1–3]. This vision follows the path taken previously by the micro-electronics and micro-optics fields. The advantages and strengths of the specific field, in our case quantum optics and atomic physics, are combined with the technological potential of microfabrication and (large scale) integration to build a robust platform for implementation of quantum operations. An important ingredient in developing such an integrated, micro-fabricated approach to manipulating atoms, molecules, or ions is the fabrication of the devices. The possibilities to combine vastly different technologies is thereby a key factor. This creates the technological basis for combining the best of the different quantum worlds of photons, atoms and solid-state in a single integrated quantum device. This overview of atom chip fabrication is organized as follows: We first discuss the challenges to be faced when starting to conceive and fabricate chips for the (quantum) manipulation of atoms. We then describe the various ingredients and the corresponding fabrication methods. We focus not only on the currently most active and successful areas – current carrying wires and integrated photonics, but also look at more visionary approaches, examples being superconducting chips or the manipulation of atoms with real nanostructures such as carbon nanotubes. Here we explicitly discuss the material engineering and fabrication of atom chips for the manipulation of neutral atoms, but the same concept of robustness and versatility through miniaturization and integration can also be applied to manipulate (polar) molecules, ions, or trapped electrons.

Enhancing photon collection from quantum emitters in diamond

Abstract: Diamond has recently become one of the leading candidates for applications in quantum communication and quantum computing. Diamond color centers are ideal as single photon sources. In this article we give an overview of the various techniques that can be used to improve the collection of photons from these emitters. These range from solid immersion lenses to Purcell-enhancement in microstructures and microcavities.

Electron beam driven alkali metal atom source for loading a magneto-optical trap in a cryogenic environment

Abstract: We present a versatile and compact electron beam driven source for alkali metal atoms, which can be implemented in cryostats. With a heat load of less than 10 mW, the heat dissipation normalized to the atoms loaded into the magneto-optical trap (MOT) is about a factor 1000 smaller than for a typical alkali metal dispenser. The measured linear scaling of the MOT loading rate with electron current observed in the experiments indicates that electron stimulated desorption is the corresponding mechanism to release the atoms.

Integrated circuits for matter waves

Abstract: Electrons join the growing technology to build integrated quantum circuits that guide matter waves on a chip.