arXiv subjects

J. H. Müller

Publications and source records attributed to J. H. Müller.

At least 19 recordsLinked to original sources

arXiv2025

Deterministic coupling of ultracold atomic lattice to a suspended photonic waveguide

The deterministic control of light-matter interactions at the level of single particles and on subwavelength scales is central to quantum optics and hybrid integrated quantum technologies. However, combining cold atom research with nanophotonic devices in a fully controllable platform remains a major experimental challenge. Here, we demonstrate the deterministic coupling of an ultracold atomic lattice to light propagating in suspended on-chip photonic circuits. These capabilities open avenues to address scalability challenges in neutral-atom quantum computers and simulators, enabling fast optical readout, efficient and subwavelength non-diffracting interaction zones, and genuine compatibility with integrated solid-state photon sources, detectors, and stop-band modulators. Beyond controllable quantum matter, the platform also enables in-situ imaging of evanescent fields of light and nanoscale structures, including prospects for three-dimensional scanning microscopy with non-invasive single-atom probes for quantum sensing applications.

quant-ph↗

arXiv2018

Observation of quantum spin noise in a 1D light-atoms quantum interface

We observe collective quantum spin states of an ensemble of atoms in a one-dimensional light-atom interface. Strings of hundreds of cesium atoms trapped in the evanescent fiel of a tapered nanofiber are prepared in a coherent spin state, a superposition of the two clock states. A weak quantum nondemolition measurement of one projection of the collective spin is performed using a detuned probe dispersively coupled to the collective atomic observable, followed by a strong destructive measurement of the same spin projection. For the coherent spin state we achieve the value of the quantum projection noise 40 dB above the detection noise, well above the 3 dB required for reconstruction of the negative Wigner function of nonclassical states. We analyze the effects of strong spatial inhomogeneity inherent to atoms trapped and probed by the evanescent waves. We furthermore study temporal dynamics of quantum fluctuations relevant for measurement-induced spin squeezing and assess the impact of thermal atomic motion. This work paves the road towards observation of spin squeezed and entangled states and many-body interactions in 1D spin ensembles.

quant-ph↗

arXiv2016

Semi-classical Dynamics of Superradiant Rayleigh Scattering in a Bose-Einstein Condensate

Due to its coherence properties and high optical depth, a Bose-Einstein condensate provides an ideal setting to investigate collective atom-light interactions. Superradiant light scattering in a Bose-Einstein condensate is a fascinating example of such an interaction. It is an analogous process to Dicke superradiance, in which an electronically inverted sample decays collectively, leading to the emission of one or more light pulses in a well-defined direction. Through time-resolved measurements of the superradiant light pulses emitted by an end-pumped BEC, we study the close connection of superradiant light scattering with Dicke superradiance. A 1D model of the system yields good agreement with the experimental data and shows that the dynamics results from the structures that build up in the light and matter-wave fields along the BEC. This paves the way for exploiting the atom-photon correlations generated by the superradiance.

quant-ph↗

arXiv2016

Coherent backscattering of light off one-dimensional atomic strings

We present the first experimental realization of coherent Bragg scattering off a one-dimensional (1D) system -- two strings of atoms strongly coupled to a single photonic mode -- realized by trapping atoms in the evanescent field of a tapered optical fiber (TOF), which also guides the probe light. We report nearly 12% power reflection from strings containing only about one thousand cesium atoms, an enhancement of two orders of magnitude compared to reflection from randomly positioned atoms. This result paves the road towards collective strong coupling in 1D atom-photon systems. Our approach also allows for a straightforward fiber connection between several distant 1D atomic crystals.

physics.atom-ph↗

arXiv2014

Generation and detection of a sub-Poissonian atom number distribution in a one-dimensional optical lattice

We demonstrate preparation and detection of an atom number distribution in a one-dimensional atomic lattice with the variance $-14$ dB below the Poissonian noise level. A mesoscopic ensemble containing a few thousand atoms is trapped in the evanescent field of a nanofiber. The atom number is measured through dual-color homodyne interferometry with a pW-power shot noise limited probe. Strong coupling of the evanescent probe guided by the nanofiber allows for a real-time measurement with a precision of $\pm 8$ atoms on an ensemble of some $10^3$ atoms in a one-dimensional trap. The method is very well suited for generating collective atomic entangled or spin-squeezed states via a quantum non-demolition measurement as well as for tomography of exotic atomic states in a one-dimensional lattice.

quant-ph↗

arXiv2014

Quantum interference of a single spin excitation with a macroscopic atomic ensemble

We report on the observation of quantum interference of a collective single spin excitation with a spin ensemble of $N_{\text{atom}} =10^5$ atoms. Detection of a single photon scattered from the atoms creates the single spin excitation, a Fock state embedded in the collective spin of the ensemble. The state of the atomic ensemble is then detected by tomography via a quantum non-demolition measurement of the collective spin. A macroscopic difference of the order of $\sqrt{N_{\text{atom}}}$ in the marginal distribution of the collective spin state arises from the interference between the single excited spin and $N_{\text{atom}}$ atoms. The hybrid discrete-continuous processing of the collective spin pave the road towards generation of even more exotic states for quantum information processing, precision measurements and communication.

quant-ph↗

arXiv2012

Towards quantum state tomography of a single polariton state of an atomic ensemble

We present a proposal and a feasibility study for the creation and quantum state tomography of a single polariton state of an atomic ensemble. The collective non-classical and non-Gaussian state of the ensemble is generated by detection of a single forward scattered photon. The state is subsequently characterized by atomic state tomography performed using strong dispersive light-atoms interaction followed by a homodyne measurement on the transmitted light. The proposal is backed by preliminary experimental results showing projection noise limited sensitivity and a simulation demonstrating the feasibility of the proposed method for detection of a non-classical and non-Gaussian state of the mesoscopic atomic ensemble. This work represents the first attempt of hybrid discrete-continuous variable quantum state processing with atomic ensembles.

quant-ph↗

arXiv2011

The effect of light assisted collisions on matter wave coherence in superradiant Bose-Einstein condensates

We investigate experimentally the effects of light assisted collisions on the coherence between momentum states in Bose-Einstein condensates. The onset of superradiant Rayleigh scattering serves as a sensitive monitor for matter wave coherence. A subtle interplay of binary and collective effects leads to a profound asymmetry between the two sides of the atomic resonance and provides far bigger coherence loss rates for a condensate bathed in blue detuned light than previously estimated. We present a simplified quantitative model containing the essential physics to explain our experimental data and point at a new experimental route to study strongly coupled light matter systems.

cond-mat.quant-gas↗

arXiv2008

Rayleigh superradiance and dynamic Bragg gratings in an end-pumped Bose-Einstein condensate

We study experimentally superradiant Rayleigh scattering from a Bose-Einstein condensate (BEC) in a new parameter regime where pump depletion and the exchange of photons between the endfire modes are important. Through experiments and simulations we show that collective atom light coupling leads to the self-organized formation of dynamic Bragg gratings within the sample. These gratings lead to an efficient back-scattering of pump photons and optical resonator structures within the BEC.

cond-mat.other↗

arXiv2003

Asymmetric Landau-Zener tunneling in a periodic potential

Using a simple model for nonlinear Landau-Zener tunneling between two energy bands of a Bose-Einstein condensate in a periodic potential, we find that the tunneling rates for the two directions of tunneling are not the same. Tunneling from the ground state to the excited state is enhanced by the nonlinearity, whereas in the opposite direction it is suppressed. These findings are confirmed by numerical simulations of the condensate dynamics. Measuring the tunneling rates for a condensate of rubidium atoms in an optical lattice, we have found experimental evidence for this asymmetry.

cond-mat.soft↗

arXiv2002

Hitting a BEC with a comb: Evolution of interference patterns inside a magnetic trap

We study the evolution inside a harmonic trap of Bose-Einstein condensates released from the periodic potential of an optical lattice. After a time-of-flight, harmonic motion of the interference peaks is observed as well as a breathing motion in the direction perpendicular to the optical lattice. We interpret these results in terms of a simple physical model and discuss the possibility of more detailed studies of such a system.

cond-mat.soft↗

arXiv2002

Dynamics and phase evolution of Bose-Einstein condensates in one-dimensional optical lattices

We report experimental results on the dynamics and phase evolution of Bose-Einstein condensates in 1D optical lattices. The dynamical behaviour is studied by adiabatically loading the condensate into the lattice and subsequently switching off the magnetic trap. In this case, the condensate is free to expand inside the periodic structure of the optical lattice. The phase evolution of the condensate, on the other hand, can be studied by non-adiabatically switching on the periodic potential. We observe decays and revivals of the interference pattern after a time-of-flight.

cond-mat↗

arXiv2002

Excitation and damping of collective modes of a Bose-Einstein condensate in a one-dimensional lattice

The mode structure of a Bose-Einstein condensate non-adiabatically loaded into a one-dimensional optical lattice is studied by analyzing the visibility of the interference pattern as well as the radial profile of the condensate after a time-of-flight. A simple model is proposed that predicts the short-time decrease of the visibility as a function of the condensate parameters. In the radial direction, heavily damped oscillations are observed, as well as an increase in the condensate temperature. These findings are interpreted as a re-thermalization due to dissipation of the initial condensate excitations into high-lying modes.

cond-mat.soft↗

arXiv2002

Photoionization of ultracold and Bose-Einstein condensed Rb atoms

Photoionization of a cold atomic sample offers intriguing possibilities to observe collective effects at extremely low temperatures. Irradiation of a rubidium condensate and of cold rubidium atoms within a magneto-optical trap with laser pulses ionizing through 1-photon and 2-photon absorption processes has been performed. Losses and modifications in the density profile of the remaining trapped cold cloud or the remaining condensate sample have been examined as function of the ionizing laser parameters. Ionization cross-sections were measured for atoms in a MOT, while in magnetic traps losses larger than those expected for ionization process were measured.

physics.atom-ph↗

arXiv2002

Free expansion of a Bose-Einstein condensate in a 1D optical lattice

We have experimentally investigated the free expansion of a Bose-Einstein condensate in an array of two-dimensional traps created by a one-dimensional optical lattice. If the condensate held in a magnetic trap is loaded adiabatically into the lattice, the increase in chemical potential due to the additional periodic potential is reflected in the expansion of the condensate after switching off the magnetic trap. We have calculated the chemical potential from measurements of the transverse expansion of the condensate as a function of the lattice parameters.

cond-mat.soft↗

arXiv2002

Experimental properties of Bose-Einstein condensates in 1D optical lattices: Bloch oscillations, Landau-Zener tunneling and mean-field effects

We report experimental results on the properties of Bose-Einstein condensates in 1D optical lattices. By accelerating the lattice, we observed Bloch oscillations of the condensate in the lowest band, as well as Landau-Zener (L-Z) tunneling into higher bands when the lattice depth was reduced and/or the acceleration of the lattice was increased. The dependence of the L-Z tunneling rate on the condensate density was then related to mean-field effects modifying the effective potential acting on the condensate, yielding good agreement with recent theoretical work. We also present several methods for measuring the lattice depth and discuss the effects of the micromotion in the TOP-trap on our experimental results.

cond-mat.soft↗

arXiv2001

Bloch oscillations and mean-field effects of Bose-Einstein condensates in 1-D optical lattices

We have loaded Bose-Einstein condensates into one-dimensional, off-resonant optical lattices and accelerated them by chirping the frequency difference between the two lattice beams. For small values of the lattice well-depth, Bloch oscillations were observed. Reducing the potential depth further, Landau-Zener tunneling out of the lowest lattice band, leading to a breakdown of the oscillations, was also studied and used as a probe for the effective potential resulting from mean-field interactions as predicted by Choi and Niu [Phys. Rev. Lett. {\bf 82}, 2022 (1999)]. The effective potential was measured for various condensate densities and trap geometries, yielding good qualitative agreement with theoretical calculations.

cond-mat.soft↗

arXiv2001

Coherent acceleration and Landau-Zener tunneling of Bose-Einstein condensates in 1-D optical lattices

We have loaded Bose-Einstein condensates into one-dimensional, off-resonant optical lattices and accelerated them by chirping the frequency difference between the two lattice beams. For small values of the lattice well-depth, Bloch oscillations were observed. Landau-Zener tunneling out of the lowest lattice band, leading to a breakdown of the oscillations, was also studied. In order to allow in-trap measurements of these phenomena, we dynamically compensated for the intrinsic micromotion of the atoms in our time-orbiting potential trap.

cond-mat↗