arXiv subjects

Jörg Helge Müller

Publications and source records attributed to Jörg Helge Müller.

6 recordsLinked to original sources

arXiv2026

Entanglement-enhanced optical magnetometry beyond the standard quantum limit

Optical atomic magnetometry is a powerful tool for continuous sensing applications, yet, in the absence of quantum correlations, its sensitivity is limited by the standard quantum limit (SQL) stemming from a trade-off between optical probe imprecision and quantum measurement backaction. Beyond-SQL sensitivity requires quantum correlations that modify these measurement noise sources. Here we demonstrate such sensitivity by using entangled state of the probe light and by engineering correlations between measurement imprecision and backaction. Having first explored SQL in a broad range of frequencies, we demonstrate overcoming the limit by combining variational readout with coupling the magnetometer to one mode of a bipartite entangled light state and conditioning the results on the other entangled mode. Tuning the detected light quadratures and combining the signals from the two measurement channels, we achieve sensitivity beyond the SQL in a broad range of acoustic frequencies which has so far remained inaccessible to quantum-noise-limited optical magnetometry.

quant-ph↗

arXiv2025

Hybrid quantum network for sensing in the acoustic frequency range

Ultimate limits for sensing of fields and forces are set by the quantum noise of a sensor. Entanglement allows for suppression of such noise and for achieving sensitivity beyond standard quantum limits. Applicability of quantum optical sensing is often restricted by fixed wavelengths of available photonic quantum sources. Another ubiquitous limitation is associated with challenges of achieving quantum-noise-limited sensitivity in the acoustic noise frequency range relevant for a number of applications. Here we demonstrate a novel tool for broadband quantum sensing by performing quantum state processing that can be applied to a wide range of the optical spectrum, and by suppressing quantum noise over an octave in the acoustic frequency range. An atomic spin ensemble is strongly coupled to one of the frequency-tunable beams of an Einstein-Podolsky-Rosen (EPR) source of light. The other EPR beam of light, entangled with the first one, is tuned to a disparate wavelength. Engineering the spin ensemble to act as a negative- or positive-mass oscillator we demonstrate frequency-dependent quantum noise reduction for measurements at the disparate wavelength. The tunability of the spin ensemble allows to target quantum noise in a variety of systems with dynamics ranging from kHz to MHz. As an example of the broadband quantum noise reduction in the acoustic frequency range, we analyse the applicability of our approach to gravitational wave detectors. Other possible applications include continuous-variable quantum repeaters and distributed quantum sensing.

quant-ph↗

arXiv2023

Acoustic frequency atomic spin oscillator in the quantum regime

We experimentally demonstrate quantum behavior of a macroscopic atomic spin oscillator in the acoustic frequency range. Quantum back-action of the spin measurement, ponderomotive squeezing of light, and oscillator spring softening are observed at spin oscillation frequencies down to 6 kHz. Quantum noise sources characteristic of spin oscillators operating in the near-DC frequency range are identified and means for their mitigation are presented. These results constitute an important step towards quantum noise reduction and entanglement-enhanced sensing in the acoustic range using a negative-mass reference frame. In particular, the results are relevant for broadband noise reduction in gravitational wave detectors.

quant-ph↗

arXiv2023

Collectively enhanced Ramsey readout by cavity sub- to superradiant transition

When an inverted ensemble of atoms is tightly packed on the scale of its emission wavelength or when the atoms are collectively strongly coupled to a single cavity mode, their dipoles will align and decay rapidly via a superradiant burst. However, a spread-out dipole phase distribution theory predicts a required minimum threshold of atomic excitation for superradiance to occur. Here we experimentally confirm this predicted threshold for superradiant emission on a narrow optical transition when exciting the atoms transversely and show how to take advantage of the resulting sub- to superradiant transition. A $π/2$-pulse places the atoms in a subradiant state, protected from collective cavity decay, which we exploit during the free evolution period in a corresponding Ramsey pulse sequence. The final excited state population is read out via superradiant emission from the inverted atomic ensemble after a second $π/2$-pulse, and with minimal heating this allows for multiple Ramsey sequences within one experimental cycle. Our scheme is a fundamentally new approach to atomic state readout characterized by its speed, simplicity, and high sensitivity. It demonstrates the potential of sensors using collective effects in cavity-coupled quantum emitters.

quant-ph↗

arXiv2023

Sub-Natural Linewidth Superradiant Lasing with Cold $^{88}$Sr Atoms

Superradiant lasers operate in the bad-cavity regime, where the phase coherence is stored in the spin state of an atomic medium rather than in the intracavity electric field. Such lasers use collective effects to sustain lasing and could potentially reach considerably lower linewidths than a conventional laser. Here, we investigate the properties of superradiant lasing in an ensemble of ultracold $^{88}$Sr atoms inside an optical cavity. We extend the superradiant emission on the 7.5 kHz wide $^3P_1$ $\rightarrow$ $^1S_0$ intercombination line to several milliseconds, and observe steady parameters suitable for emulating the performance of a continuous superradiant laser by fine tuning the repumping rates. We reach a lasing linewidth of 820 Hz for 1.1 ms of lasing, nearly an order of magnitude lower than the natural linewidth

physics.atom-ph↗

arXiv2017

Dipole force free optical control and cooling of nanofiber trapped atoms

The evanescent field surrounding nano-scale optical waveguides offers an efficient interface between light and mesoscopic ensembles of neutral atoms. However, the thermal motion of trapped atoms, combined with the strong radial gradients of the guided light, leads to a time-modulated coupling between atoms and the light mode, thus giving rise to additional noise and motional dephasing of collective states. Here, we present a dipole force free scheme for coupling of the radial motional states, utilizing the strong intensity gradient of the guided mode and demonstrate all-optical coupling of the cesium hyperfine ground states and motional sideband transitions. We utilize this to prolong the trap lifetime of an atomic ensemble by Raman sideband cooling of the radial motion, which has not been demonstrated in nano-optical structures previously. Our work points towards full and independent control of internal and external atomic degrees of freedom using guided light modes only.

physics.atom-ph↗