arXiv subjects

Jörg Schmiedmayer

Publications and source records attributed to Jörg Schmiedmayer.

121 records · Page 7Linked to original sources

arXiv2011

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

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 to measure the coupling strength and temperature and hence a full characterization of the system.

cond-mat.quant-gas↗

arXiv2010

Cavity QED with an ultracold ensemble on a chip: prospects for strong magnetic coupling at finite temperatures

We study the nonlinear dynamics of an ensemble of cold trapped atoms with a hyperfine transition magnetically coupled to a resonant microwave cavity mode. Despite the minute single atom coupling one obtains strong coupling between collective hyperfine qubits and microwave photons enabling coherent transfer of an excitation between the long lived atomic qubit state and the mode. Evidence of strong coupling can be obtained from the cavity transmission spectrum even at finite thermal photon number. The system makes it possible to study further prominent collective phenomena such as superradiant decay of an inverted ensemble or the building of a narrowband stripline micromaser locked to an atomic hyperfine transition.

quant-ph↗

arXiv2009

Ramsey interference in one dimensional systems: The full distribution function of fringe contrast as a probe of many-body dynamics

We theoretically analyze Ramsey interference experiments in one dimensional quasi-condensates and obtain explicit expressions for the time evolution of full distribution functions of fringe contrast. We show that distribution functions contain unique signatures of the many-body mechanism of decoherence. We argue that Ramsey interference experiments provide a powerful tool for analyzing strongly correlated nature of 1D interacting systems.

cond-mat.quant-gas↗

arXiv2009

An integrated atom detector: single atoms and photon statistics

We demonstrate a robust fiber-optics-based fluorescence detector, fully integrated on an atom chip, which detects single atoms propagating in a guide with 66% efficiency. We characterize the detector performance and the atom flux by analyzing the photon statistics. Near-perfect photon antibunching proves that single atoms are detected, and allows us to study the second-order intensity correlation function of the fluorescence over three orders of magnitude in atomic density.

quant-ph↗

arXiv2009

A simple integrated single-atom detector

We present a reliable and robust integrated fluorescence detector capable of detecting single atoms. The detector consists of a tapered lensed single-mode fiber for precise delivery of excitation light and a multimode fiber to collect the fluorescence. Both are mounted in lithographically defined SU-8 holding structures on an atom chip. Rb87 atoms propagating freely in a magnetic guide are detected with an efficiency of up to 66%, and a signal-to-noise ratio in excess of 100 is obtained for short integration times.

physics.atom-ph↗

arXiv2008

A millisecond quantum memory for scalable quantum networks

Scalable quantum information processing critically depends on the capability of storage of a quantum state. In particular, a long-lived storable and retrievable quantum memory for single excitations is of crucial importance to the atomic-ensemble-based long-distance quantum communication. Although atomic memories for classical lights and continuous variables have been demonstrated with milliseconds storage time, there is no equal advance in the development of quantum memory for single excitations, where only around 10 $μ$s storage time was achieved. Here we report our experimental investigations on extending the storage time of quantum memory for single excitations. We isolate and identify distinct mechanisms for the decoherence of spin wave (SW) in atomic ensemble quantum memories. By exploiting the magnetic field insensitive state, ``clock state", and generating a long-wavelength SW to suppress the dephasing, we succeed in extending the storage time of the quantum memory to 1 ms. Our result represents a substantial progress towards long-distance quantum communication and enables a realistic avenue for large-scale quantum information processing.

quant-ph↗

arXiv2008

Designing potentials by sculpturing wires

Magnetic trapping potentials for atoms on atom chips are determined by the current flow in the chip wires. By modifying the shape of the conductor we can realize specialized current flow patterns and therefore micro-design the trapping potentials. We have demonstrated this by nano-machining an atom chip using the focused ion beam technique. We built a trap, a barrier and using a BEC as a probe we showed that by polishing the conductor edge the potential roughness on the selected wire can be reduced. Furthermore we give different other designs and discuss the creation of a 1D magnetic lattice on an atom chip.

cond-mat.mtrl-sci↗

arXiv2008

Multi-layer atom chips for versatile atom micro manipulation

We employ a combination of optical UV- and electron-beam-lithography to create an atom chip combining sub-micron wire structures with larger conventional wires on a single substrate. The new multi-layer fabrication enables crossed wire configurations, greatly enhancing the flexibility in designing potentials for ultra cold quantum gases and Bose-Einstein condensates. Large current densities of >6 x 10^7 A/cm^2 and high voltages of up to 65 V across 0.3 micron gaps are supported by even the smallest wire structures. We experimentally demonstrate the flexibility of the next generation atom chip by producing Bose-Einstein condensates in magnetic traps created by a combination of wires involving all different fabrication methods and structure sizes.

physics.atom-ph↗

arXiv2007

Synchronized Independent Narrow-band Single Photons and Efficient Generation of Photonic Entanglement

We create independent, synchronized single-photon sources with built-in quantum memory based on two remote cold atomic ensembles. The synchronized single photons are used to demonstrate efficient generation of entanglement. The resulting entangled photon pairs violate a Bell's Inequality by 5 standard deviations. Our synchronized single photons with their long coherence time of 25 ns and the efficient creation of entanglement serve as an ideal building block for scalable linear optical quantum information processing.

quant-ph↗

arXiv2006

A Deterministic and Storable Single-Photon Source Based on Quantum Memory

A single photon source is realized with a cold atomic ensemble ($^{87}$Rb atoms). In the experiment, single photons, which is initially stored in an atomic quantum memory generated by Raman scattering of a laser pulse, can be emitted deterministically at a time-delay in control. It is shown that production rate of single photons can be enhanced by a feedback circuit considerably while the single-photon quality is conserved. Thus our present single-photon source is well suitable for future large-scale realization of quantum communication and linear optical quantum computation.

quant-ph↗

arXiv2005

Detecting magnetically guided atoms with an optical cavity

We show that a low finesse cavity can be efficient for detecting neutral atoms. The low finesse can be compensated for by decreasing the mode waist of the cavity. We have used a near concentric resonator with a beam waist of 12$μ$m and a finesse of only 1100 to detect magnetically guided Rb atoms with a detection sensitivity of 0.1 atom in the mode volume. For future experiments on single atom detection and cavity QED applications, it should be very beneficial to use miniaturized optical resonator integrated on atom chips.

physics.atom-ph↗

arXiv2000

A Beam Splitter for Guided Atoms on an Atom Chip

We have designed and experimentally studied a simple beam splitter for atoms guided on an Atom Chip, using a current carrying Y-shaped wire and a bias magnetic field. This beam splitter and other similar designs can be used to build atom optical elements on the mesoscopic scale, and integrate them in matterwave quantum circuits.

quant-ph↗

arXiv1999

Atom Chips

Atoms can be trapped and guided using nano-fabricated wires on surfaces, achieving the scales required by quantum information proposals. These Atom Chips form the basis for robust and widespread applications of cold atoms ranging from atom optics to fundamental questions in mesoscopic physics, and possibly quantum information systems.

quant-ph↗