arXiv subjects

W. Ertmer

Publications and source records attributed to W. Ertmer.

72 records · Page 4Linked to original sources

arXiv2003

Three level atom optics via the tunneling interaction

Three level atom optics (TLAO) is introduced as a simple, efficient and robust method to coherently manipulate and transport neutral atoms. The tunneling interaction among three trapped states allows to realize the spatial analog of the stimulated Raman adiabatic passage (STIRAP), coherent population trapping (CPT), and electromagnetically induced transparency (EIT) techniques. We investigate a particular implementation in optical microtrap arrays and show that under realistic parameters the coherent manipulation and transfer of neutral atoms among dipole traps could be realized in the millisecond range.

quant-ph↗

arXiv2003

Measurement of the Spatial Correlation Function of Phase Fluctuating Bose-Einstein Condensates

We measure the intensity correlation function of two interfering spatially displaced copies of a phase fluctuating Bose-Einstein Condensate (BEC). It is shown that this corresponds to a measurement of the phase correlation properties of the initial condensate. Analogous to the method used in the stellar interferometer experiment of Hanbury Brown and Twiss, we use spatial intensity correlations to determine the phase coherence lengths of elongated BECs. We find good agreement with our prediction of the correlation function and confirm the expected coherence length.

cond-mat.soft↗

arXiv2003

Spectroscopy of Dark Soliton States in Bose-Einstein Condensates

Experimental and numerical studies of the velocity field of dark solitons in Bose-Einstein condensates are presented. The formation process after phase imprinting as well as the propagation of the emerging soliton are investigated using spatially resolved Bragg-spectroscopy of soliton states in Bose-Einstein condensates of Rubidium87. A comparison of experimental data to results from numerical simulations of the Gross-Pitaevskii equation clearly identifies the flux underlying a dark soliton propagating in a Bose-Einstein condensate. The results allow further optimization of the phase imprinting method for creating collective exitations of Bose-Einstein condensates.

cond-mat↗

arXiv2002

Characterization and control of phase fluctuations in elongated Bose-Einstein condensates

Quasi one dimensional Bose-Einstein condensates (BECs) in elongated traps exhibit significant phase fluctuations even at very low temperatures. We present recent experimental results on the dynamic transformation of phase fluctuations into density modulations during time-of-flight and show the excellent quantitative agreement with the theoretical prediction. In addition we confirm that under our experimental conditions, in the magnetic trap density modulations are strongly suppressed even when the phase fluctuates. The paper also discusses our theoretical results on control of the condensate phase by employing a time-dependent perturbation. Our results set important limitations on future applications of BEC in precision atom interferometry and atom optics, but at the same time suggest pathways to overcome these limitations.

cond-mat.soft↗

arXiv2002

Interferometer-Type Structures for Guided Atoms

We experimentally demonstrate interferometer-type guiding structures for neutral atoms based on dipole potentials created by micro-fabricated optical systems. As a central element we use an array of atom waveguides being formed by focusing a red-detuned laser beam with an array of cylindrical microlenses. Combining two of these arrays, we realize X-shaped beam splitters and more complex systems like the geometries for Mach-Zehnder and Michelson-type interferometers for atoms.

quant-ph↗

arXiv2002

Quantum computing with spatially delocalized qubits

We analyze the operation of quantum gates for neutral atoms with qubits that are delocalized in space, i.e., the computational basis states are defined by the presence of a neutral atom in the ground state of one out of two trapping potentials. The implementation of single qubit gates as well as a controlled phase gate between two qubits is discussed and explicit calculations are presented for rubidium atoms in optical microtraps. Furthermore, we show how multi-qubit highly entangled states can be created in this scheme.

quant-ph↗

arXiv2002

Microoptical Realization of Arrays of Selectively Addressable Dipole Traps: A Scalable Configuration for Quantum Computation with Atomic Qubits

We experimentally demonstrate novel structures for the realisation of registers of atomic qubits: We trap neutral atoms in one and two-dimensional arrays of far-detuned dipole traps obtained by focusing a red-detuned laser beam with a microfabricated array of microlenses. We are able to selectively address individual trap sites due to their large lateral separation of 125 mu m. We initialize and read out different internal states for the individual sites. We also create two interleaved sets of trap arrays with adjustable separation, as required for many proposed implementations of quantum gate operations.

quant-ph↗

arXiv2002

Phase Fluctuations in Bose-Einstein Condensates

We demonstrate the existence of phase fluctuations in elongated Bose-Einstein Condensates (BECs) and study the dependence of those fluctuations on the system parameters. A strong dependence on temperature, atom number, and trapping geometry is observed. Phase fluctuations directly affect the coherence properties of BECs. In particular, we observe instances where the phase coherence length is significantly smaller than the condensate size. Our method of detecting phase fluctuations is based on their transformation into density modulations after ballistic expansion. An analytic theory describing this transformation is developed.

cond-mat↗

arXiv2001

Dynamics of dark solitons in elongated Bose-Einstein condensates

We find two types of moving dark soliton textures in elongated Bose-Einstein condensates: non-stationary kinks and proper dark solitons. The former have a curved notch region and rapidly decay by emitting phonons and/or proper dark solitons. The proper moving solitons are characterized by a flat notch region and we obtain the diagram of their dynamical stability. At finite temperatures the dynamically stable solitons decay due to the thermodynamic instability. We develop a theory of their dissipative dynamics and explain experimental data.

cond-mat.stat-mech↗

arXiv2001

Quantum Information Processing with Microfabricated Optical Elements

We discuss a new direction in the field of quantum information processing with neutral atoms. It is based on the use of microfabricated optical elements. With these elements versatile and integrated atom optical devices can be created in a compact fashion. This approach opens the possibility to scale, parallelize, and miniaturize atom optics for new investigations in fundamental research and applications towards quantum computing with neutral atoms. The exploitation of the unique features of the quantum mechanical behavior of matter waves and the capabilities of powerful state-of-the-art micro- and nanofabrication techniques lend this approach a special attraction.

quant-ph↗

arXiv2001

Observation of Phase Fluctuations in Bose-Einstein Condensates

The occurrence of phase fluctuations due to thermal excitations in Bose-Einstein condensates (BECs) is studied for a variety of temperatures and trap geometries. We observe the statistical nature of the appearence of phase fluctuations and characterize the dependence of their average value on temperature, number of particles and the trapping potential. We find pronounced phase fluctuations for condensates in very elongated traps in a broad temperature range. The results are of great importance for the realization of BEC in quasi 1D geometries, for matter wave interferometry with BECs, as well as for coherence properties of guided atom laser beams.

cond-mat.stat-mech↗

arXiv2001

Doppler cooling and trapping on forbidden transitions

Ultracold atoms at temperatures close to the recoil limit have been achieved by extending Doppler cooling to forbidden transitions. A cloud of ^40Ca atoms has been cooled and trapped to a temperature as low as 6 μK by operating a magneto-optical trap on the spin-forbidden intercombination transition. Quenching the long-lived excited state with an additional laser enhanced the scattering rate by a factor of 15, while a high selectivity in velocity was preserved. With this method more than 10% of pre-cooled atoms from a standard magneto-optical trap have been transferred to the ultracold trap. Monte-Carlo simulations of the cooling process are in good agreement with the experiments.

physics.atom-ph↗

arXiv2001

Atom Optics with Microfabricated Optical Elements

We introduce a new direction in the field of atom optics, atom interferometry, and neutral-atom quantum information processing. It is based on the use of microfabricated optical elements. With these elements versatile and integrated atom optical devices can be created in a compact fashion. This approach opens the possibility to scale, parallelize, and miniaturize atom optics for new investigations in fundamental research and application. It will lead to new, compact sources of ultracold atoms, compact sensors based on matter wave interference and new approaches towards quantum computing with neutral atoms. The exploitation of the unique features of the quantum mechanical behavior of matter waves and the capabilities of powerful state-of-the-art micro- and nanofabrication techniques lend this approach a special attraction.

quant-ph↗

arXiv2000

Wave Packet Echoes in the Motion of Trapped Atoms

We experimentally demonstrate and systematically study the stimulated revival (echo) of motional wave packet oscillations. For this purpose, we prepare wave packets in an optical lattice by non-adiabatically shifting the potential and stimulate their reoccurence by a second shift after a variable time delay. This technique, analogous to spin echoes, enables one even in the presence of strong dephasing to determine the coherence time of the wave packets. We find that for strongly bound atoms it is comparable to the cooling time and much longer than the inverse of the photon scattering rate.

quant-ph↗

arXiv2000

A Waveguide for Bose-Einstein Condensates

We report on the creation of Bose-Einstein condensates of $^{87}$Rb in a specially designed hybrid, dipole and magnetic trap. This trap naturally allows the coherent transfer of matter waves into a pure dipole potential waveguide based on a doughnut beam. Specifically, we present studies of the coherence of the ensemble in the hybrid trap and during the evolution in the waveguide by means of an autocorrelation interferometer scheme. By monitoring the expansion of the ensemble in the waveguide we observe a mean field dominated acceleration on a much longer time scale than in the free 3D expansion. Both the autocorrelation interference and the pure expansion measurements are in excellent agreement with theoretical predictions of the ensemble dynamics.

cond-mat↗

arXiv1999

Dark Solitons in Bose-Einstein Condensates

Dark solitons in cigar shaped Bose-Einstein condensates of Rubidium-87 are created by a phase imprinting method. Coherent and dissipative dynamics of the solitons has been observed.

cond-mat↗

arXiv1999

Coherent Evolution of Bouncing Bose-Einstein Condensates

We investigate the evolution of Bose-Einstein condensates falling under gravity and bouncing off a mirror formed by a far-detuned sheet of light. After reflection, the atomic density profile develops splitting and interference structures which depend on the drop height, on the strength of the light sheet, as well as on the initial mean field energy and size of the condensate. We compare experimental results with simulations of the Gross-Pitaevski equation. A comparison with the behaviour of bouncing thermal clouds allows to identify quantum features specific for condensates.

cond-mat↗

arXiv1999

Optical Generation of Vortices in trapped Bose-Einstein Condensates

We demonstrate numerically the efficient generation of vortices in Bose-Einstein condensates (BEC) by using a ``phase imprinting'' method. The method consist of passing a far off resonant laser pulse through an absorption plate with azimuthally dependent absorption coefficient, imaging the laser beam onto a BEC, and thus creating the corresponding non-dissipative Stark shift potential and condensate phase shift. In our calculations we take into account experimental imperfections. We also propose an interference method to detect vortices by coherently pushing part of the condensate using optically induced Bragg scattering.

cond-mat.stat-mech↗