In a standard two-level Ramsey interferometer, the measured phase accumulates linearly during the interrogation time. Here, we introduce three-level Ramsey interferometry that employs a noncyclic geometric phase response to enhance phase sensing, with projected internal-path interference reshaping the mapping from accumulated signal phase to readout phase. Near a geodesic-closure transition, a small accumulated signal phase produces a sharply amplified readout-phase shift. We quantify the accompanying gain--visibility tradeoff and identify a finite operating window in which the amplified response yields a net signal-to-noise-ratio gain under technical-noise-limited conditions. By tuning an initial Ramsey phase offset, this high-slope window can be positioned at a desired operating point and sampled repeatedly with shorter cycles, providing a geometric shortcut to improved projected stability. More broadly, these results establish a multilevel Ramsey route to enhanced phase sensitivity in quantum platforms, where two signal-collecting internal paths interfere to produce a noncyclic geometric response.
In a standard two-level Ramsey interferometer, the measured phase accumulates linearly during the interrogation time. Here, we introduce three-level Ramsey interferometry that employs a noncyclic geometric phase response to enhance phase sensing, with projected internal-path interference reshaping the mapping from accumulated signal phase to readout phase. Near a geodesic-closure transition, a small accumulated signal phase produces a sharply amplified readout-phase shift. We quantify the accompanying gain--visibility tradeoff and identify a finite operating window in which the amplified response yields a net signal-to-noise-ratio gain under technical-noise-limited conditions. By tuning an initial Ramsey phase offset, this high-slope window can be positioned at a desired operating point and sampled repeatedly with shorter cycles, providing a geometric shortcut to improved projected stability. More broadly, these results establish a multilevel Ramsey route to enhanced phase sensitivity in quantum platforms, where two signal-collecting internal paths interfere to produce a noncyclic geometric response.
High-precision measurements are crucial for testing the fundamental laws of nature and advancing the technological frontier. Clock interferometry, where particles with an internal clock are coherently split and recombined along two spatial paths, has sparked interest due to its fundamental implications, especially at the intersection of quantum mechanics and general relativity. Here, we demonstrate that a clock interferometer provides metrological improvement compared to its technical noise-limited counterpart using a single internal quantum state. This enhancement around a critical working point can be interpreted as a geometric phase-induced signal-to-noise ratio gain. In our experimental setup, we infer a sensitivity enhancement of 8.8 decibels when measuring a small difference between external fields. We estimate that tens of decibels of sensitivity enhancement could be attained for measurements with a higher atom flux. This opens the door to developing a superior probe for fundamental physics and a high-performance sensor for various technological applications.
Ramsey interferometry estimates a detuning from the phase accumulated between two interaction zones, with a resolution set by the interrogation time τ. We propose a single-qudit extension based on Wigner-Majorana (WM) spin-j dynamics, whose internal levels form a multipath interferometer. The enhancement is not generic: ideal QFTD and XD sequences do not densify the central fringe under the population readouts considered. Instead, in manifolds that realize the WM coupling, it arises from coherences between separated ladder states created and recombined by a single near-resonant drive per Ramsey zone. For the qutrit, preparing the central state of a spin-1 WM manifold and measuring its return probability gives P3(Δ)=cos2(Δτ), versus the qubit P2(Δ)=cos2(Δτ/2). The central fringe is thus compressed twofold at fixed τ and the maximal slope doubled in the ideal limit, with contrast ideally unity. For higher-dimensional WM manifolds (odd and even D) the central response sharpens with dimension, but the signal spreads over several channels; we introduce a scalar readout from nearest-neighbor shoulder populations and quantify the resolution-contrast trade-off via the slope SD and contrast CD. We also study robustness to diagonal phase noise from probe-shift fluctuations: under projector-type common-mode dephasing, the WM readouts are less contrast-sensitive than the qubit readout. The robustness is symmetry-selective, not universal: for linear Zeeman dephasing (L=Jz), the large m-separation that compresses the fringe also enhances dephasing, so higher-dimensional readouts become more sensitive, not protected. The WM qutrit is thus a practical operating point for enhanced Ramsey spectroscopy at fixed τ; higher qudits trade extra slope for reduced contrast.
We theoretically investigate geometric Stückelberg interferometry in a doubly driven optical lattice clock (OLC). By tuning the relative phase between the two driving fields, we control the relative sign of the effective coupling strengths at the avoided crossings. Within the adiabatic-impulse model, we analyze the time evolution of the two-level system, where nonadiabatic transitions occur only near the crossing points and adiabatic evolution takes place between them. We show that, besides the usual dynamical phase and the Stokes phase, a gauge-invariant noncyclic geometric phase contributes to the final transition probability. This geometric contribution yields a stable π-phase shift in the Stückelberg interference fringes. Moreover, we demonstrate that, under realistic experimental conditions, this geometric Stückelberg interferometer remains insensitive to inhomogeneities in atom-light coupling arising from the finite temperature of the atomic ensemble. Our results provide a general framework for engineering and detecting geometric phases on the OLC platform.
Coherent control and braiding of anyons remain central challenges in realizing topologically protected quantum operations. We propose a Ramsey interferometry protocol to directly access the geometric phases associated with anyons in fractional Chern insulators. Our approach employs impurities with individually addressable internal states that bind to the anyons, allowing their adiabatic motion and exchange under full spatial control. By combining Ramsey and spin-echo sequences using one and two impurities, the protocol gives independent access to the Aharonov-Bohm and exchange contributions to the total geometric phase, thereby providing an unambiguous probe of anyonic statistics. Our scheme can potentially be implemented in cold-atom quantum simulators as well as in van der Waals heterostructures. Complementary finite-size simulations in non-interacting Chern insulators quantify the system sizes required to faithfully extract geometric phases, highlighting the role of edge effects. Our results establish impurity-based interferometry as a feasible route toward direct anyon braiding experiments in quantum simulators and lay the groundwork for future explorations of non-Abelian braiding and topological quantum control.
I will present our development of global-phase spectroscopy, a Rabi-like metrological protocol inspired by geometric control techniques originally introduced for holonomic quantum gates and based on detuning-dependent Aharonov–Anandan phase. Applied to an optical clock transition, we deployed this method to realize quantum-amplified, time-reversal spectroscopy, yielding 2.4(7) dB metrological gain and 4.0(8) dB laser-noise suppression beyond the standard quantum limit. I will focus on the key metrological advantages of global-phase spectroscopy: i) an intrinsically favorable scaling of sensitivity to local-oscillator high-frequency noise (compared to for Rabi and for Ramsey), and, unlike standard Rabi spectroscopy, ii) featuring quantum enhancement when operated with entangled collective states, such as spin-squeezed inputs. I will close by connecting these results to the broader QIS-NP landscape, highlighting opportunities for applying this protocol to (other) nuclear-spin qubits, nuclear clocks, and other emerging quantum-enhanced sensing and quantum-information platforms.
This work presents a geometric–topological field model in which the affine connection is treated as the sole fundamental dynamical variable, while metric structure, matter, and effective particle dynamics emerge as secondary descriptions. Matter is interpreted as localized, topologically nontrivial configurations of the connection field. A central prediction of the model is that quantum interference is sensitive to geometric complexity, leading to a geometry-dependent suppression of interference visibility and a geometry-induced phase accumulation. These effects are investigated in the context of atom interferometry, with particular emphasis on Mach–Zehnder and large-momentum-transfer (LMT) configurations. Interference fringes are analyzed to extract visibility, and an exponential suppression law as a function of geometric complexity is observed. Statistical robustness is assessed using bootstrap resampling, yielding a strictly positive suppression coefficient. In addition to visibility loss, a geometry-dependent linear phase accumulation is identified, with different rates for simple and complex interferometer geometries. The results suggest that quantum coherence can be interpreted as an emergent manifestation of underlying geometric constraints, and that atom interferometry provides a direct experimental probe of such geometric effects. The presented framework yields clear, falsifiable interferometric signatures that can be tested with existing experimental platforms.