arXiv subjects

Enno Giese

Publications and source records attributed to Enno Giese.

At least 19 recordsLinked to original sources

arXiv2026

Fermion quantum field theory on curved and non-inertial backgrounds in standard-Minkowski form

Quantum field theory on curved and non-inertial backgrounds contains background- and foliation-dependent quantities in the canonical Lagrangian, the hypersurface inner product and bilinear form, as well as in the equal-time anti-commutation relations. In this work, we determine a local fermion-field redefinition that brings these canonical structures into their standard-Minkowski forms, i. e., the forms they assume in Cartesian inertial coordinates on Minkowski spacetime, where the zeroth world coordinate is identified as the coordinate of time. Starting from the generally covariant Dirac action minimally coupled to a spin-1 gauge field, we derive the corresponding Lagrangian, fermionic inner product, and quantization rule in an Arnowitt-Deser-Misner decomposition, formulated in arbitrary world coordinates. We identify the generalized temporal gamma matrix as the common geometric factor governing the canonical temporal structure of all three quantities. Using a field redefinition, we transform this generalized temporal gamma matrix to its standard-Minkowski form, thereby mapping the fermionic inner product and the equal-time anti-commutation relation to their standard-Minkowski expressions, while transferring the explicit background and foliation dependence to the transformed Lagrangian and fermion-field operators. We show that such a field redefinition necessarily consists of a local rescaling and a fixing of the local Lorentz frame. This procedure restores the conventional canonical normalization from standard-Minkowski spacetime used for fermionic mode quantization and occupation-number operators. The transformed Lagrangian consequently assumes a generalized first-order Schr\"odinger form, leading to the familiar rest-energy term and spacetime-magnetic couplings, as well as to the leading non-relativistic limit, in which temporal derivatives are separated from spatial ones.

hep-th↗

arXiv2026

Phase estimation in spontaneous nonlinear interferometry for enhanced quantum imaging

Bicolor quantum imaging can reach, in principle, phase supersensitivity approaching the Heisenberg limit using squeezed light from high-gain parametric down-conversion, but established quantum-imaging setups typically operate in the low-gain, spontaneous regime, where such scaling is inaccessible. Here, we show experimentally and theoretically that a symmetric nonlinear interferometer, even in the spontaneous regime, retains a phase-sensitivity advantage over configurations where entanglement is not exploited as a quantum-metrological resource, although the achievable phase sensitivity remains shot-noise-limited. This advantage appears as a shift of the optimal working point toward the dark fringe, the low-gain signature of the mechanism underlying high-gain supersensitivity. We derive design choices for phase-optimized nonlinear interferometers accordingly, favoring configurations that exploit entanglement as a metrological resource and specifying their optimal operating point.

quant-ph↗

arXiv2026

Generalized Foldy-Wouthuysen approach for the derivation of non-relativistic effective field theories

Effective field theories (EFTs) are a powerful framework for performing high-precision calculations at reduced complexity compared to their fundamental counterparts. A particularly important class of EFTs arises in the non-relativistic (NR) regime. Their construction relies on a different realization of the underlying symmetries, since Lorentz invariance is no longer manifest in covariant form in the NR regime. This behavior imposes a link between certain matching coefficients, and therefore additional constraints, commonly referred to as hidden Lorentz invariance. These constraints are established in quantum field theories on inertial flat spacetime, such as NR quantum electrodynamics. However, deriving these constraints becomes considerably more involved for theories involving physics beyond the Standard Model or formulated in non-inertial spacetime backgrounds, where the hidden symmetry structure is less transparent. In this work, we present an approach to obtain the NR EFT by first constructing a relativistic EFT and then performing a generalized NR reduction based on an extended Foldy-Wouthuysen transformation. We illustrate this method by a quantum chromo-electrodynamics EFT for inertial flat spacetime, describing both electromagnetic and strong interactions, and show how it reduces to the established Lagrangian of NR quantum chromodynamics and electrodynamics. The hidden Lorentz invariance emerges as a direct consequence of the construction. This approach provides a route to obtain the NR limits of more complex theories, \eg Dirac fields in non-inertial spacetime or extensions involving physics beyond the Standard Model. As an example, we apply the method to add the coupling of a pseudoscalar axion field in a simplified model and derive its NR limit.

hep-ph↗

arXiv2026

Technical Proposal for the Atom Interferometer CERN Experiment (AICE) Facility

We present the technical proposal for the Atom Interferometer CERN Experiment (AICE), a $\mathcal{O}(100)$ m vertical atom interferometer to be installed against the wall of the PX46 access shaft to the LHC. AICE is conceived as a versatile and flexible long-baseline atom-interferometry facility whose primary scientific goal is probing for bosonic ultralight dark matter (ULDM) in a mass range inaccessible to other experiments, with a secondary goal of pioneering the exploration of gravitational waves (GWs) with frequencies in the range ${\sim}$0.03-3 Hz as a pathfinder for future longer-baseline detectors. The initial configuration employs ultracold $^{87}$Sr atoms in a single-photon 698-nm interferometer with three shaft-based atom sources in a multi-source gradiometer geometry, supported by one surface reference source for laser stabilisation and diagnostics, to target scalar ULDM. Operation with $^{88}$Sr will give sensitivity to axion-like particles (ALPs), vector ULDM with $B-L$ couplings and violation of the principle of equivalence, while a $^{171}$Yb upgrade will improve the sensitivity to $B-L$ couplings and equivalence violations. Probing the Einstein equivalence principle (EP) and measuring $\alpha$ will proceed in parallel with the ULDM searches. A conceptual feasibility study and a detailed technical implementation study have established that PX46 is a uniquely mature and implementation-ready site, with no technical showstoppers. Completing site preparation works during LS3 would enable the subsequent installation and operation of AICE without impacting HL-LHC operations. The detector design builds on the VLBAI and MAGIS experiments and the AION-10 Technical Design Report, scaling the strontium gradiometer architecture to the $\sim$100 m baseline. AICE is endorsed by the TVLBAI Proto-Collaboration, comprising 57 institutions in 22 countries.

hep-ex↗

arXiv2026

Balancing Quasi-Bragg Regime and Velocity Selectivity in Quantum-Enhanced Atom Interferometry

Spin squeezing in atomic ensembles enables atom interferometry with sensitivities below the shot-noise limit, but the associated entanglement is highly susceptible to loss, making imperfections in atom optics a central limitation. Bragg diffraction is an established technique for driving transitions between atomic momentum states and enables large-momentum transfer through higher-order diffraction while preserving the internal state. However, it is intrinsically limited by two competing mechanisms: Short light pulses induce parasitic diffraction into off-resonant orders beyond an effective two-level description, while long pulses face velocity selectivity. We derive analytical expressions in a second-quantized framework for the atom optics and phase uncertainty of a Mach-Zehnder interferometer including these effects. We demonstrate that sub-shot-noise scaling is achieved only in a regime of intermediate pulse duration. Furthermore, we show that deleterious effects of higher-order diffraction are partially mitigated by optimizing the input quantum state.

quant-ph↗

arXiv2026

Parameter Estimation from Amplitude Collapse in Correlated Matter-Wave Interference

Operating matter-wave interferometers as quantum detectors for fundamental physics or inertial sensors with unprecedented accuracies relies on noise rejection, often implemented by correlating multiple sensors. They can be spatially separated (gradiometry or gravitational-wave detection) or consist of different internal states (magnetometry or quantum clock interferometry), with a signal-amplitude modulation serving as a signature of a differential phase. In this work, we introduce Parameter Estimation from Amplitude Collapse (PEAC) by applying statistical inference techniques for different magnetically sensitive substates of an atom interferometer. We demonstrate that PEAC provides higher trueness, resulting in a substantially reduced bias compared to standard methods for perfectly correlated signals, while achieving competitive precision near, but not at, vanishing amplitudes. This indicates that vanishing signals do not constitute the most favourable working point for high-accuracy sensing, relevant to quantum clock interferometry. PEAC presents a generally applicable complementary evaluation method for correlated interferometers without phase stability, increasing the overall accuracy and enabling applications beyond atom-based interferometry.

quant-ph↗

arXiv2026

Below-shot-noise capacity in phase estimation using nonlinear interferometers

Over the past decade, several schemes for imaging and sensing based on nonlinear interferometers have been proposed and demonstrated experimentally. These interferometers exhibit two main advantages. First, they enable probing a sample at a chosen wavelength while detecting light at a different wavelength with high efficiency (bicolor quantum imaging and sensing with undetected light). Second, they can show quantum-enhanced sensitivities below the shot-noise limit, potentially reaching Heisenberg-limited precision in parameter estimation. Here, we compare three quantum-imaging configurations using only easily accessible intensity-based measurements for phase estimation: a Yurke-type SU(1,1) interferometer, a Mandel-type induced-coherence interferometer, and a hybrid scheme that continuously interpolates between them. While an ideal Yurke interferometer can exhibit Heisenberg scaling, this advantage is known to be fragile under realistic detection constraints and in the presence of loss. We demonstrate that differential intensity detection in the Mandel interferometer provides the highest and most robust phase sensitivity among the considered schemes, reaching but not surpassing the shot-noise limit, even in the presence of loss. Intensity measurements in a Yurke-type configuration can achieve genuine sub-shot-noise sensitivity under balanced losses and moderate gain; however, their performance degrades in realistic high-gain regimes. Consequently, in this regime, the Mandel configuration with differential detection outperforms the Yurke-type setup and constitutes the most robust approach for phase estimation.

quant-ph↗

arXiv2025

An epsilon-near-zero-based nonlinear platform for ultrafast re-writable holography

We re-examine real-time holography for all-optical structuring of light and optical computation using a contemporary material: a subwavelength-thick, spatially unstructured film of indium tin oxide (ITO). When excited by spatially structured light at epsilon-near-zero frequencies, the film acts as an efficient and reconfigurable diffractive optical platform for all-optical modulation of light such as spatial structuring and optical computations. We demonstrate a few percent of absolute diffraction efficiency over greater than 300 nm bandwidth around telecom wavelengths using a film four orders of magnitude thinner than and up to six orders of magnitude faster than standard holographic materials. Our findings highlight the potential of using epsilon-near-zero-based nanostructures for efficient modulation of spatially structured light and rapid prototyping without complex nanofabrication processes.

physics.optics↗

arXiv2025

Entanglement and Its Verification: A Tutorial on Classical and Quantum Correlations

Entanglement, a defining property of quantum mechanics in which two physical subsystems cannot be seen as independent entities, challenges our everyday experience and classical intuition. However, only such strong quantum correlations enable quantum technologies, including quantum computing or communication, while revealing the limits of our classical worldview by violating local realism. Given its importance in modern quantum science, we present this tutorial addressing the questions: What is entanglement, how does it differ from classical correlations, and how can it be experimentally verified? Using celebrated examples, such as Schr\"odinger's cat, we highlight the distinction between classical and quantum correlations and illustrate the definition of entangled and separable states. We review entanglement criteria by discussing Heisenberg-type uncertainty relations for continuous variables and the CHSH inequality for discrete systems. Focusing on concepts of quantum correlations and operational entanglement witnesses, we provide accessible tools and illustrative examples aimed at demystifying entanglement for a broad readership.

quant-ph↗

arXiv2025

Unified laboratory-frame analysis of atomic gravitational-wave sensors

Atomic sensors using light-matter interactions, in particular atomic clocks and atom interferometers, have the potential to complement optical gravitational-wave detectors in the mid-frequency regime. Although both rely on interference, the interfering components of clocks are spatially colocated, whereas atom interferometers are based on spatial superpositions. Both the electromagnetic fields that drive the transitions and generate superpositions, while propagating through spacetime, as well as the atoms themselves as massive particles are influenced by gravitational waves, leading to effective potentials that induce phase differences inferred by the sensor. In this work, we analyze the effects of these potentials on atomic clocks and atom interferometers in the laboratory frame. We show that spatial superpositions in atom interferometers, both light-pulse and guided ones, give rise to a gravitational-wave signal. Although these spatial superpositions are suppressed for clocks, we show that the light pulses driving internal transitions measure the spatial distance between the centers of two separate clocks. We highlight that this mechanism only yields a sensitivity if both clocks, including possible trapping setups, move on geodesics given by the gravitational wave. While such configurations are natural for satellite free-fliers, terrestrial optical clocks usually rely on stationary traps, rendering them insensitive to leading order. Moreover, we show that both sensors can be enhanced by composite interrogation protocols in a common framework. To this end, we propose a pulse sequence that can be used for large-momentum-transfer atom interferometers and for hyper-echo atomic clocks, leading to a signal enhancement and noise suppression.

quant-ph↗

arXiv2025

Spatial and Pulse Efficiency Constraints in Atom Interferometric Gravitational Wave Detectors

Currently planned and constructed terrestrial detectors for gravitational waves and dark matter based on differential light-pulse atom interferometry are designed around three primary strategies to enhance their sensitivity: (i) Resonant-mode enhancement using multiple diamonds, (ii) large-momentum-transfer techniques to increase arm separation within the interferometer, and (iii) very-long baseline schemes that increase the distance between the two interferometers. Both resonant-mode enhancement and large-momentum-transfer techniques result in a greater number of light pulses, making high pulse fidelity during atom-light interactions imperative. At the same time, increasing the number of diamonds in vertical configurations leads to taller atomic fountains, which consequently reduces the available distance between interferometers. As a result, the number of diamonds, large-momentum-transfer pulses, and the fountain height are interdependent parameters that must be carefully balanced. In this work, we present optimal configurations for multi-diamond geometries, explicitly accounting for the spatial extent of a single interferometer, considering constraints imposed by the baseline dimensions and atomic losses due to imperfect pulses. We provide practical analytical relations to estimate the optimal number of pulses that should be applied. Many proposals beyond demonstrator experiments require pulse numbers that demand efficiencies not yet demonstrated with state-of-the-art momentum transfer techniques. As a result, the observed sensitivity falls short of expectations - an effect caused by both arm separation and atom loss per pulse - highlighting the urgent need for research aimed at improving pulse fidelities.

quant-ph↗

arXiv2025

Space magnetometry with a differential atom interferometer

Atom interferometers deployed in space are excellent tools for high precision measurements, navigation, or Earth observation. In particular, differential interferometric setups feature common-mode noise suppression and enable reliable measurements in the presence of ambient platform noise. Here we report on orbital magnetometry campaigns performed with differential single- and double-loop interferometers in NASA's Cold Atom Lab aboard the International Space Station. By comparing measurements with atoms in magnetically sensitive and insensitive states, we have realized atomic magnetometers mapping magnetic field curvatures. Our results pave the way towards precision quantum sensing missions in space.

physics.atom-ph↗

arXiv2025

Finite-Speed-of-Light Effects in Atom Interferometry: Diffraction Mechanisms and Resonance Conditions

Light-pulse atom interferometers serve as tools for high-precision metrology and are targeting measurements of relativistic effects. This development is facilitated by extended interrogation times and large-momentum-transfer techniques generating quantum superpositions of both interferometer arms on large distances. Due to the finite speed of light, diffracting light pulses cannot interact simultaneously with both arms, inducing phase perturbations that compromise the accuracy of the sensor -- an effect that becomes progressively important as spatial separations increase. For a consistent framework, we develop a theory for finite-speed-of-light effects in atom interferometers alongside with other relativistic effects such as the mass defect. Our analysis shows that their magnitude depends crucially on the diffraction mechanism and the specific interferometer geometry. We demonstrate that the velocity of the atomic cloud at the mirror pulse of a Mach-Zehnder interferometer is less critical than the precise tuning of the lasers for resonant diffraction. Finally, we propose an experiment to test our predictions based on recoilless transitions and discuss mitigation strategies to reduce the bias in gravimetric applications.

quant-ph↗

arXiv2025

Sensing Birefringence and Diattenuation with Undetected Light

Developing advanced technologies for sensing and imaging biological samples is crucial for medical applications, making quantum-enhanced methods particularly valuable, as they promise significant benefits over classical techniques. An important aspect of biological imaging is the characterization of tissue, which often involves resolving complex structural information such as birefringence and diattenuation. These measures require polarization-sensitive sensing which remains largely unaddressed in quantum-imaging techniques with undetected light. However, the bicolor nature and supreme phase sensitivity of nonlinear interferometers make them particularly advantageous for biological sensing. Hence, we theoretically introduce controllable polarizations of the interrogating light in a quantum-imaging setup and show the potential of nonlinear interferometers to simultaneously sense birefringence and diattenuation with undetected light while discussing both the low- and high-gain regime.

quant-ph↗

arXiv2025

Long-Baseline Atom Interferometry

Long-baseline atom interferometry is a promising technique for probing various aspects of fundamental physics, astrophysics and cosmology, including searches for ultralight dark matter (ULDM) and for gravitational waves (GWs) in the frequency range around 1~Hz that is not covered by present and planned detectors using laser interferometry. The MAGIS detector is under construction at Fermilab, as is the MIGA detector in France. The PX46 access shaft to the LHC has been identified as a very suitable site for an atom interferometer of height $\sim 100$m, sites at the Boulby mine in the UK and the Canfranc Laboratory are also under investigation, and possible sites for km-class detectors have been suggested. The Terrestrial Very-Long-Baseline Atom Interferometry (TVLBAI) Proto-Collaboration proposes a coordinated programme of interferometers of increasing baselines.

hep-ex↗

arXiv2024

Terrestrial Very-Long-Baseline Atom Interferometry: Summary of the Second Workshop

This summary of the second Terrestrial Very-Long-Baseline Atom Interferometry (TVLBAI) Workshop provides a comprehensive overview of our meeting held in London in April 2024, building on the initial discussions during the inaugural workshop held at CERN in March 2023. Like the summary of the first workshop, this document records a critical milestone for the international atom interferometry community. It documents our concerted efforts to evaluate progress, address emerging challenges, and refine strategic directions for future large-scale atom interferometry projects. Our commitment to collaboration is manifested by the integration of diverse expertise and the coordination of international resources, all aimed at advancing the frontiers of atom interferometry physics and technology, as set out in a Memorandum of Understanding signed by over 50 institutions.

hep-ex↗

arXiv2024

Synthetic Quantum Holography with Undetected Light

Utilizing nonlinear interferometers for sensing with undetected light enables new sensing and imaging techniques in spectral ranges that are difficult to detect. To enhance this method for future applications, it is advantageous to extract both amplitude and phase information of an object. This study introduces two approaches for synthetic quantum holography with undetected light, which allows for obtaining an object's amplitude and phase information in a nonlinear interferometer by capturing only a single image. One method is based on quasi-phase-shifting holography using superpixel structures displayed on a spatial light modulator. The other method relies on synthetic off-axis holography implemented through a linear phase gradient on a spatial light modulator. Both approaches are experimentally analyzed for applicability and compared against available multi-acquisition methods.

physics.optics↗

arXiv2024

Conservation of angular momentum on a single-photon level

Identifying conservation laws is central to every subfield of physics, as they illuminate the underlying symmetries and fundamental principles. A prime example can be found in quantum optics: The conservation of orbital angular momentum (OAM) during spontaneous parametric down-conversion (SPDC) enables the generation of a photon pair with entangled OAM. In this article, we report on the first study of OAM conservation in SPDC pumped by single photons. Our results present the first implementation of cascaded down-conversion without waveguides, setting the stage for experiments on the direct generation of multi-photon high-dimensional entanglement using all degrees of freedom of light.

quant-ph↗