Quantum Metrology and Fundamental Physics - University Tübingen, Germany

15 Jul 2026, 08:00 → 17 Jul 2026, 18:00 Europe/Berlin

Aaron Vincent (IPPP, Durham University), Daniel Braun (University of Tuebingen), Michael Spannowsky (IPPP, Durham University), Stefano Moretti

Quantum metrology has emerged as one of the three fundamental pillars of the quantum technology era 2.0, alongside quantum computation and quantum communication.  It has already led to substantial scientific progress, from magnetometry with unprecedented sensitivity or spatial resolution to the detection of gravitational waves using squeezed light.  At the same time, current research in fundamental physics, such as attempts to detect dark matter or deviations from general relativity, require measurements with unprecedented sensitivities.  The goal of the workshop at the University Tübingen is therefore to bring together researchers from both communities and try to see where quantum metrology can contribute to progress in fundamental physics.  

Gefördert vom Bundesministerium für Forschung, Technologie und Raumfahrt
(BMFTR) und dem Wissenschaftsministerium Baden-Württemberg im Rahmen der Exzellenzstrategie von Bund und Ländern.

Wednesday 15 July

08:50 → 09:00 Wednesday Morning 1: Welcome

09:00 → 10:30 Wednesday Morning 1

09:00 Bounds on the strength of a spin-independent fifth force: Current reach of hydrogen and helium spectroscopy

It has long been recognised that high‑precision hydrogen spectroscopy places stringent bounds on the strength of a hypothetical new spin‑independent interaction [1,2]. The earlier work in this area has since been extended to the spectroscopy of deuterium, muonic hydrogen, muonic deuterium, helium and muonic helium [3-6], as well as to other theoretical and experimental inputs [7]. These later results and the current experimental status will be briefly reviewed in this talk. The impact of the latest high-precision measurements in hydrogen and helium on constraints on such a fifth force will be outlined. In particular, it will be shown that the recent high‑precision measurement of the 2S-6P interval in hydrogen [8] enables especially tight bounds to be placed on the strength of a new interaction coupling electrons to protons for mediator masses between 0.1 and 10 keV/$c^2$.

[1] S. G. Karshenboim, Phys. Rev. D 82, 073003 (2010).
[2] J. Jaeckel and S. Roy, Phys. Rev. D 82, 125020 (2010).
[3] C. Delaunay, C. Frugiuele, E. Fuchs, and Y. Soreq, Phys. Rev. D 96, 115002 (2017).
[4] M. P. A. Jones, R. M. Potvliege, and M. Spannowsky, Phys. Rev. Res. 2, 013244 (2020).
[5] R. M. Potvliege, A. Nicolson, M. P. A. Jones, and M. Spannowsky,
Phys. Rev. A 108, 052825 (2023).
[6] R. M. Potvliege, New. J. Phys. 27, 045002 (2025).
[7] C. Delaunay et al., Phys. Rev. Lett. 130, 121801 (2023).
[8] L. Maisenbacher et al., Nature 650, 845 (2026).

Speaker: Dr Robert Potvliege (Durham University, Physics Department)

09:45 Searching for ultralight bosons with quantum sensors

Ultralight bosons provide well-motivated candidates for physics beyond the Standard Model and may couple weakly to photons or fermions. If sourced by laboratory-scale objects, such fields can generate long-range potentials that imprint measurable phase shifts or induce currents in superconducting Josephson systems. In particular, an oscillating axion dark matter background can produce an Aharonov-Bohm-like phase in an rf-SQUID loop, where the resulting axion-induced current may modify the voltage readout in the presence of an external magnetic field. Similarly, ultralight axions can mix with photons, and an adiabatically varying magnetic field can generate an axion-induced Berry phase in a Mach-Zehnder interferometer. I will discuss how such precision measurements of these geometric and topological phases offer a quantum interferometric route to probe ultralight bosons and their feeble couplings to Standard Model particles.

Speaker: Tanmay Kumar Poddar (IPPP, Durham University)

10:30 → 11:00 Break

11:00 → 12:30 Wednesday Morning 2

11:00 Searching for Solar Dark Photons and Axions with Coherent Two-Photon Transitions

Abstract. Two-photon transitions in a coherently prepared atomic medium support cooperative emission rates that scale as $N^{2}$, where $N$ is the number of emitters in the coherence volume. Because the two signal photons are emitted back-to-back, their momenta cancel and the Dicke phase-matching constraint met, so that the coherence volume can be made macroscopic. Together these features make such a medium a natural detector for ultralight dark sectors, whose small Standard Model couplings would otherwise restrict searches to narrow resonant haloscope or helioscope cavities.

Building on prior frameworks of Bhoonah, Bramante and Song, and others, I extend the construction into two new source classes. In the helioscope channels, solar dark photons and solar axions are converted to real photons either at a conducting plate (kinetic mixing $\chi$) or inside a magnetised bore (Primakoff $g_{a\gamma\gamma}$), and the resulting field seeds a broadband trigger in the coherently prepared sample. In the haloscope channels the same conversion is driven instead by the non-relativistic galactic halo and produces a narrowband stochastic trigger. The helioscope channels yield broadband sensitivity from sub-meV to eV-scale masses; the haloscope channels improve on existing dark-photon dark-matter constraints near the parahydrogen two-photon resonance at $\omega_{\mathrm{res}}\simeq 0.26~\mathrm{eV}$. I discuss the robustness of these projections, the regime in which the $N^{2}$ enhancement persists, and the implications for the CATCHY experimental program at Queen's University.

Speaker: Rohan Kulkarni (Queen's University)

11:45 Searching for Sub-GeV Dark Matter with superfluid helium

I will present novel ideas to search for the scattering of dark matter particles with mass below the GeV scale using superfluid helium detectors. First, I will introduce the upcoming DELight experiment, which will use magnetic microcalorimeters to detect photons and collective excitations produced by dark matter scattering. The sensitivity of such a search can be extended further by considering electron excitations induced by nuclear scattering via the so-called Migdal effect. Finally, I will discuss the effective field theory relevant for even lighter particles (below the MeV scale) and how sensitivity may be extended into this regime using optomechanical cavities and single-photon detection.

Speaker: Felix Kahlhoefer (Karlsruhe Institute of Technology)

12:30 → 14:00 Lunch

14:00 → 15:30 Wednesday Afternoon 1

14:00 Local precision limits in quantum metrology under unitary driving

Although the local precision limits of thermal equilibrium metrology are well established, the potential to enhance precision by driving a system into nonequilibrium remains largely unexplored. We first demonstrate that the precision limit of thermal equilibrium metrology can be surpassed by applying a unitary drive to the initial thermal equilibrium state. Our central result is to establish the supremum of the quantum Fisher information (QFI) under arbitrary unitary driving. We show that an optimized single quench is already sufficient to outperform thermal equilibrium metrology. Moreover, we identify an optimal protocol to achieve the supremum. Perhaps counter-intuitively, this QFI supremum is attainable by applying only two optimized quenches to the initial thermal equilibrium state. These findings provide both the fundamental precision limit and the optimal control strategies for local quantum metrology under unitary driving.

Speaker: Takanao Ishii (The University of Tokyo)

14:45 Experimental considerations in searches for new physics with cold atoms

I will discuss experimental aspects of new physics searches with cold atoms. The focus will be on Rydberg states of cold hydrogen and deuterium atoms and their application to searches for additional ``fifth forces’’ [1,2]. In particular, I will explore the experimental challenge of realizing cold, trapped samples of hydrogen and deuterium [3,4] and some possible solutions. I will also consider experiments involving entangled atomic clocks in a gravitational potential that pose a challenge to the framework of general relativity.

[1] M. P. A. Jones, R. M. Potvliege, and M. Spannowsky, Phys. Rev. Res. 2, 013244 (2020).
[2] R. M. Potvliege, A. Nicolson, M. P. A. Jones, and M. Spannowsky, Phys. Rev. A 108, 052825 (2023).
[3] J. P. Scott, R. M. Potvliege D. Carty and M. P. A. Jones, Metrologia 61, 025001 (2024).
[4] O. Amit at al., J. Phys. Conference Series 2889, 012027 (2024).
[5] J. Borregaard and I. Pikovski, Phys. Rev. Res. 7, 023192 (2025).

Speaker: Matthew Jones (Durham)

15:30 → 16:00 Break

16:00 → 17:30 Wednesday Afternoon 2

16:00 Towards detecting the gravitational field of ultra-relativistic proton bunches at the LHC

The gravitational field of ultra-relativistic particles has never been measured. The LHC proton beam at γ ≈ 7500 offers a unique terrestrial source to probe gravity in this regime, where scalar-tensor theories predict deviations from general relativity. We characterise the spectral properties of the gravitational signal arising from realistic beam-filling patterns, explore modulation strategies to enhance detectability, and assess the noise requirements for a realistic experimental setup.

Speaker: Shubhang Dadhich (University of Tübingen)

16:45 Designing Open Quantum Systems for Enabling Quantum-Enhanced Sensing through Classical Measurements

Quantum systems in nonequilibrium conditions, where coherent many-body interactions compete with dissipative effects, can feature rich phase diagrams and emergent critical behavior. Associated collective effects, together with the continuous observation of quanta dissipated into the environment—typically photons—allow one to achieve quantum-enhanced parameter estimation [1]. However, protocols for tapping this enhancement typically involve intricate measurements on the combined system-environment state [2-4]. Here, we show that many-body quantum enhancement can in fact be obtained through classical measurements such as photon counting and homodyne detection. We illustrate this in detail for a class of open spin-boson models, which can be realized in trapped-ion or cavity QED setups. Our findings highlight a route toward the design of systems that enable a practical implementation of quantum-enhanced metrology through continuous classical measurements.

Publication:
R. Mattes, A. Cabot, F. Carollo, and I. Lesanovsky, Designing open quantum systems for enabling quantum enhanced sensing through classical measurements, Phys. Rev. Lett. 135, 230402 (2025)

References:
[1] A. Cabot, F. Carollo, and I. Lesanovsky, Exploiting nonequilibrium phase transitions and strong symmetries for continuous measurement of collective observables, Phys. Rev. A 110, L060601 (2024)
[2] S. Gammelmark and K. Mølmer, Fisher information and the quantum Cramér-Rao sensitivity limit of continuous measurements, Phys. Rev. Lett. 112, 170401 (2014)
[3] D. Yang, S. F. Huelga, and M. B. Plenio, Efficient information retrieval for sensing via continuous measurement, Phys. Rev. X 13, 031012 (2023)
[4] A. Khan, F. Albarelli, and A. Datta, A tensor network approach to sensing quantum light-matter interactions,PRX Quantum 6, 040343 (2025)

Speaker: Robert Mattes

Thursday 16 July

09:00 → 10:30 Thursday morning 1

09:00 A quantum algorithm for the n-gluon MHV scattering amplitude

We propose a quantum algorithm for computing the n-gluon maximally helicity violating (MHV) tree-level scattering amplitude. We revisit a newly proposed method for unitarisation of non-unitary operations and present how this implementation can be used to create quantum gates responsible for the color and kinematic factors of the gluon scattering amplitude. As a proof-of-concept, we detail the full conceptual algorithm that yields the squared amplitude and implement the corresponding building blocks on simulated noiseless quantum circuits for n = 4 to analyze its performance. The algorithm is found to perform well with parameter optimizations, suggesting it to be a good candidate for implementing on quantum computers also for higher multiplicities.

Speaker: Erik Bashore (Uppsala University)

A quantum algorithm for the n-gluon MHV scattering amplitude

09:45 Continuous sensing for non-Markovian systems

In noisy quantum metrology, information about an unknown parameter is lost to the environment and thus inaccessible for any measurement on the system alone. Continuously monitoring the reservoir's output allows to partially recover the lost information, quantified by the unraveling quantum Fisher information (QFI) [1]. This unraveling strategy is particularly relevant for cavity- and circuit-QED platforms, where a quantum system can interact with a structured non-Markovian bath whose Markovian output can be continuously measured. However, to fully capture the memory effects of the non-Markovian bath, standard stochastic methods rely on propagating the joint system-pseudomode state [2,3], requiring the simulation of exponentially large Hilbert spaces. Here, we overcome this limitation by formulating continuous quantum parameter estimation within the framework of the conditioned hierarchical equations of motion (cHEOM) [4]. Our approach directly maps the unraveling QFI onto the hierarchy, reducing the exponential bosonic dimensionality to a highly efficient combinatorial scaling. Applying this framework, we demonstrate that non-Markovian memory effects significantly enhance the unraveling QFI compared to Markovian limits, thereby extending the regime in which continuous environmental monitoring yields a metrological advantage.

References:
[1] F. Albarelli, M. A. Rossi, D. Tamascelli, and M. G. Genoni, “Restoring heisenberg scaling in noisy quantum metrology by monitoring the environment”, Quantum 2, 110 (2018).
[2] B. M. Garraway, “Nonperturbative decay of an atomic system in a cavity”, Phys. Rev. A 55, 2290–2303 (1997).
[3] G. Pleasance, B. M. Garraway, and F. Petruccione, “Generalized theory of pseudomodes for exact descriptions of non-markovian quantum processes”, Phys. Rev. Res. 2, 043058 (2020).
[4] V. Link, K. M¨uller, R. G. Lena, K. Luoma, F. Damanet, W. T. Strunz, and A. J. Daley, “Non-markovian quantum dynamics in strongly coupled multimode cavities conditioned on continuous measurement”, PRX Quantum 3, 020348 (2022).

Speaker: Jan Schumann (University of Tübingen)

10:30 → 11:00 Break

11:00 → 12:30 Thursday morning 2

11:00 Nonlocal correlations for bosonic fields in black hole quantum atmosphere

Abstract:
Recent developments in black hole physics suggest that Hawking radiation may originate from an extended region outside the event horizon, known as the quantum atmosphere. This motivates the study of spatially dependent quantum effects in curved spacetime.
We investigate bosonic quantum correlations in a bipartite system in the vicinity of a Schwarzschild black hole, where one subsystem remains asymptotically inertial while the other experiences the Hartle–Hawking thermal vacuum. Quantum correlations are quantified using measurement-induced nonlocality (MIN), which captures nonclassical correlations beyond entanglement.
We analyze the dependence of MIN on the local Hartle-Hawking temperature, which varies with radial distance from the black hole. Our results show that bosonic MIN exhibits a non-monotonic spatial behavior, deviating from the standard near-horizon decay. This suggests that quantum correlations are sensitive to the spatial structure of Hawking radiation and may provide signatures of the quantum atmosphere.

Key words: Black holes; quantum correlations; bosonic fields; quantum atmosphere; measurement-induced nonlocality

References

1. S. W. Hawking, Commun. Math. Phys. 43, 199 (1975).
2. J. B. Hartle and S. W. Hawking, Phys. Rev. D 13, 2188 (1976).
3. W. G. Unruh, Phys. Rev. D 14, 870 (1976).
4. S. B. Giddings, Phys. Lett. B 754, 39 (2016).
5. R. Dey, S. Liberati, and D. Pranzetti, Phys. Lett. B 774, 308 (2017).
6. S. Luo and S. Fu, Phys. Rev. Lett. 106, 120401 (2011).
7. A. Z. Kaczmarek and D. Szczesniak, Phys. Lett. B 848, 138364 (2024).
8. A. Z. Kaczmarek, D. Szczesniak, Z. Bak, and R. Szczesniak, Phys. Lett. B 868, 139683 (2025).

Speaker: johann gil (Jan Dlugosz University in Czestochowa)

11:45 Quantum estimation theory for neutrino physics

Quantum estimation theory provides a framework for quantifying the ultimate precision limits for parameter estimation in physical systems. I will introduce its basic concepts and apply them to neutrino oscillations, focusing on the estimation of the PMNS parameters.
A central puzzle is why the CP-violating phase δCP remains significantly less constrained than the other mixing parameters. Using quantum estimation tools, I will  show that this limitation is not due to a lack of information encoded in the neutrino quantum state. Instead, it arises from the suboptimal nature of standard flavor measurements, particularly near the first oscillation maximum.
I will discuss how optimized measurement strategies can improve sensitivity to δCP, and compare the achievable precision with that of other mixing parameters, for which current measurements are already close to optimal.
I will conclude by briefly discussing related applications to axion-like particle searches in light-shining-through-a-wall experiments and meson mixing.
https://arxiv.org/abs/2511.20148v1. https://arxiv.org/abs/2602.16534v1

Speaker: Claudia Frugiuele (Infn milano)

12:30 → 14:00 Lunch

14:00 → 15:30 Thursday afternoon 1

14:00 Quantum Enhanced Mode Parameter Estimation: A General Framework for Quantum Limited Imaging

We present a local framework for quantum parameter estimation in linear optical systems, where the unknown parameter is encoded through deformations of an experimentally accessible mode basis. The resulting quantum Fisher information decomposes into two distinct contributions: a coherent contribution, generated by parameter-induced dynamics within the accessible modes and capable of Heisenberg scaling, and a geometric leakage contribution, arising from coupling to inaccessible modes and limited to standard quantum scaling. This decomposition is obtained via a purification together with a minimization over Kraus representations at the working point. It depends only on the accessible mode functions, their covariance matrix, and the projector onto the accessible system subspace. We further provide a general method for constructing optimal input states that achieve Heisenberg scaling using the eigenbasis of the system generator. We apply the formalism to two-point-source imaging with a general complex point-spread function. For two-mode systems, we show that the system generator generally contains both a number term and an SU(2) mode-mixing term, both distinct from the leakage contribution. This separation identifies mode deformations that generate coherent quantum sensitivity with Heisenberg scaling, as opposed to deformations that produce only leakage into inaccessible modes and therefore exhibit standard quantum scaling. For a Gaussian point-spread function with linear and cubic phase, we find a quantum advantage in the absence of photon loss to additional environmental modes.

Speaker: Emre Kose (Instituto de Física Corpuscular (IFIC), CSIC‐Universitat de València, Spain)

14:45 Impact of phase-space structures on quantum-enhanced sensing

Quantum-chaotic dynamics in mixed phase space can enhance metrological sensitivity through mechanisms governed by global homoclinic structures. Building on a semiclassical formulation of the quantum Fisher information, we show that global homoclinic manifolds provide a practical guide to the most sensitive initial states. These manifolds organize transport near edge-of-chaos boundaries into channels with distinct accumulated responses to perturbations of the estimated parameter. Wavepackets placed on suitable channel boundaries can therefore exhibit strongly enhanced quantum Fisher information. For the quantum kicked top, we present numerical evidence that initial states selected on global homoclinic manifolds can approach Heisenberg-limited scaling with respect to both spin size and evolution time.

Speaker: Mahdi Rouhbakhshnabati (Institut für Theoretische Physik, Eberhard-Karls-Universität Tübingen, 72076 Tübingen, Germany)

15:30 → 16:00 Break

16:00 → 16:45 Thursday afternoon 2

16:00 Computational Discovery of Interferometric Gravitational Wave Detectors

Current and next-generation gravitational wave detectors are designed by human experts who must balance coupled physical effects across many domains. The vast space of all possible experiment designs suggests that many high-sensitivity, unconventional detectors may lie beyond the reach of human intuition alone. AI-based methods are increasingly capable of discovering powerful measurement schemes from first principles, offering a complementary design paradigm with biases distinct from those of human experts. We therefore frame the discovery of novel gravitational wave measurement techniques as a search for optima over a vast space of hardware configurations subject to practical constraints. We discuss how to engineer an expressive search space with the potential to discover novel detector topologies and present Differometor, a differentiable interferometer simulator built for high-performance optimization. We then formulate gravitational wave detector design as a challenging algorithmic benchmark and argue that new interpretability and analysis tools will be essential for understanding and exploiting unconventional AI-discovered detector blueprints.

Speaker: Jonathan Klimesch (University of Tübingen)

18:30 → 20:30 Conference Dinner

Friday 17 July

09:00 → 10:30 Friday morning 1

09:00 Testing new — reasonable as well as crazy — forces with atoms and ions

The exchange of new light(ish) bosons coupled to electrons and nucleons leads to extra forces and corresponding potentials between particles and even macroscopic bodies. The high accuracy achievable in measurements on atoms and ions provides a powerful laboratory to test these forces at atomic and smaller distances. We discuss new tests of axion-like particles in highly charged ions, but also atomic tests of Lorentz and even CPT violating forces.

Speaker: Joerg Jaeckel (ITP Heidelberg)

09:45 Quantum many-body sensing

I consider the quantum sensing of gravity and rotation fields
using spatially localized probes (trapped systems) of ultracold quantum gases of interacting atoms or molecules.
It is shown that to achieve an accurate statement on the optimality
of a given measurement protocol, it is mandatory to go beyond the standard quantum optics paradigm of describing the system by a Hamiltonian containing (powers of) Fock space operators with constant coefficients, which is leading e.g. to spin models. Instead, the evolution needs to be described fully self-consistently, with both Fock state occupation probabilities of the system modes
and the shape of the associated orbitals (single-particle wave functions) changing in an inter-dependent way dynamically.

Speaker: Prof. Dr. Uwe R. Fischer

10:30 → 11:00 Break

11:00 → 12:30 Friday Morning 2 - Roundtable discussion

12:30 → 14:00 Lunch