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npj Quantum Information

Coherent enhancement of collection of light from linear ion crystals

Thuy Dung Tran, Babjak, Daniel, Artem Kovalenko, Kratveer Singh, Pham, Tuan Minh, Petr Obšil, Lešundák, Adam, Číp, Ondřej, Slodička, Lukáš

Published Jul 8, 2025• 0 citations
Publisher

Abstract

The efficient detection of light from trapped ions in free space is paramount for most of their applications. We propose a scheme to enhance the photon collection from linear ion strings. It employs the constructive interference of light scattered from ions along the axial direction in linear Paul traps. The coherent enhancement of photon collection is numerically optimized for a range of feasible spatial angles and realistic ion positions in a single harmonic Coulomb potential. Despite the large mutual distance of scatterers on the order of many wavelengths of scattered light, the experimental tests presented confirm the feasibility of enhancements by a factor of 3.05 ± 0.09 with a crystal of nine 40Ca+ ions. The proposed collection geometry is intrinsic to diverse linear ion trap designs, and the methodology can be directly applied to an observation of scattering from ion crystals prepared in collective electronic excitations. The presented data resulted from measurements supported by national funding from the Ministry of Education, Youth and Sports under grant agreement No. 731473, by the QUANTERA ERA-NET cofund in quantum technologies implemented within the European Union’s Horizon 2020 Program (project PACE-IN, 8C20004), by the Czech Science Foundation under the project GA21-13265X, the Ministry of Education, Youth and Sports under the project CZ.02.01.01/00/22 008/0004649, the Ministry of Interior of the Czech Republic within the Program OPSEC under the project VK01030193, and the Palacký University grant IGA-PrF-2024-008.

DOI
10.5281/zenodo.17658710

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Coherent enhancement of collection of light from linear ion crystals

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Abstract The efficient detection of light from trapped ions in free space is paramount for most of their applications. We propose a scheme to enhance the photon collection from linear ion strings. It employs the constructive interference of light scattered from ions along the axial direction in linear Paul traps. The coherent enhancement of photon collection is numerically optimized for a range of feasible spatial angles and realistic ion positions in a single harmonic Coulomb potential. Despite the large mutual distance of scatterers on the order of many wavelengths of scattered light, the experimental tests presented confirm the feasibility of enhancements by a factor of 3.05 ± 0.09 with a crystal of nine 40 Ca + ions. The proposed collection geometry is intrinsic to diverse linear ion trap designs, and the methodology can be directly applied to an observation of scattering from ion crystals prepared in collective electronic excitations.

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Coherent enhancement of collection of light from linear ion crystals

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The efficient detection of light from trapped ions in free space is paramount for most of their applications. We propose a scheme to enhance the photon collection from linear ion strings. It employs the constructive interference of light scattered from ions along the axial direction in linear Paul traps. The coherent enhancement of photon collection is numerically optimized for a range of feasible spatial angles and realistic ion positions in a single harmonic Coulomb potential. Despite the large mutual distance of scatterers on the order of many wavelengths of scattered light, presented experimental tests confirm the feasibility of enhancements by a factor of $3.05 \pm 0.09$ with a crystal of nine $^{40}$Ca$^+$ ions. Further significant improvements using different ion species, which allow for suppression of the sensitivity to the residual thermal motion, are predicted. The proposed collection geometry is intrinsic to diverse linear ion trap designs and the methodology can be directly applied to an observation of scattering from ion crystals prepared in collective electronic excitations.

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•Jan 1, 2011•1 citation
The efficient detection of light from trapped ions in free space is paramount for most of their applications. We propose a scheme to enhance the photon collection from linear ion strings. It employs the constructive interference of light scattered from ions along the axial direction in linear Paul traps. The coherent enhancement of photon collection is numerically optimized for a range of feasible spatial angles and realistic ion positions in a single harmonic Coulomb potential. Despite the large mutual distance of scatterers on the order of many wavelengths of scattered light, the experimental tests presented confirm the feasibility of enhancements by a factor of 3.05 ± 0.09 with a crystal of nine 40Ca+ ions. The proposed collection geometry is intrinsic to diverse linear ion trap designs, and the methodology can be directly applied to an observation of scattering from ion crystals prepared in collective electronic excitations. The presented data resulted from measurements supported by national funding from the Ministry of Education, Youth and Sports under grant agreement No. 731473, by the QUANTERA ERA-NET cofund in quantum technologies implemented within the European Union’s Horizon 2020 Program (project PACE-IN, 8C20004), by the Czech Science Foundation under the project GA21-13265X, the Ministry of Education, Youth and Sports under the project CZ.02.01.01/00/22 008/0004649, the Ministry of Interior of the Czech Republic within the Program OPSEC under the project VK01030193, and the Palacký University grant IGA-PrF-2024-008.
Abstract The efficient detection of light from trapped ions in free space is paramount for most of their applications. We propose a scheme to enhance the photon collection from linear ion strings. It employs the constructive interference of light scattered from ions along the axial direction in linear Paul traps. The coherent enhancement of photon collection is numerically optimized for a range of feasible spatial angles and realistic ion positions in a single harmonic Coulomb potential. Despite the large mutual distance of scatterers on the order of many wavelengths of scattered light, the experimental tests presented confirm the feasibility of enhancements by a factor of 3.05 ± 0.09 with a crystal of nine 40 Ca + ions. The proposed collection geometry is intrinsic to diverse linear ion trap designs, and the methodology can be directly applied to an observation of scattering from ion crystals prepared in collective electronic excitations.
The efficient detection of light from trapped ions in free space is paramount for most of their applications. We propose a scheme to enhance the photon collection from linear ion strings. It employs the constructive interference of light scattered from ions along the axial direction in linear Paul traps. The coherent enhancement of photon collection is numerically optimized for a range of feasible spatial angles and realistic ion positions in a single harmonic Coulomb potential. Despite the large mutual distance of scatterers on the order of many wavelengths of scattered light, presented experimental tests confirm the feasibility of enhancements by a factor of 3.05±0.093.05 \pm 0.093.05±0.09 with a crystal of nine 40^{40}40Ca+^++ ions. Further significant improvements using different ion species, which allow for suppression of the sensitivity to the residual thermal motion, are predicted. The proposed collection geometry is intrinsic to diverse linear ion trap designs and the methodology can be directly applied to an observation of scattering from ion crystals prepared in collective electronic excitations.
Abstract The demonstration of optical multipath interference from a large number of quantum emitters is essential for the realization of many paradigmatic experiments in quantum optics. However, such interference remains still unexplored as it crucially depends on the sub-wavelength positioning accuracy and stability of all emitters. We present the observation of controlled interference of light scattered from strings of up to 53 trapped ions. The light scattered from ions localized in a harmonic trapping potential is collected along the ion crystal symmetry axis, which guarantees the spatial indistinguishability and allows for an efficient scaling of the contributing ion number. We achieve the preservation of the coherence of scattered light observable for all the measured string sizes and nearly-optimal enhancement of phase sensitivity. The presented results will enable realization and control of directional photon emission, direct detection of enhanced quadrature squeezing of atomic resonance fluorescence, or optical generation of genuine multi-partite entanglement of atoms.
The demonstration of coherence between a large number of quantum emitters is essential for the realization of many paradigmatic experiments in quantum optics. Here we present the observation of controlled interference of light scattered from crystal strings of up to 53\,trapped ions. The scattered light is collected along the crystal symmetry axis, which guarantees spatial indistinguishability of photons scattered by different ions and allows for convenient scaling of the number of contributing particles. The interference phase is tuned by changing the mutual distance between the ions and the observed pattern corresponds qualitatively to a simple theoretical model considering point-like emitters. The observed interference visibility remains in the 0.34 to 0.53 range for all the measured string sizes, limited mostly by the spatially inhomogeneous laser intensity seen by the long ion strings. The presented results open the possibility for experimental investigation of a whole range of fundamental physical phenomena, including engineered directional photon emission, direct detection of quadrature squeezing of atomic resonance fluorescence, and optical generation of genuine multi-partite entanglement between a large number of trapped ions.
In our work, we focus on the experimental demonstration of two complementary approaches to enhancing the interaction between photons and atoms at the level of individual photons and 40Ca+ ions. We implement a scheme in which the observation of light interference scattered by several trapped atomic ions is further enhanced due to interference with their mirror images. The control of the corresponding collective coherent optical scattering and the possibility of observing the interaction with light emitted by many independent ions modified by optical boundary conditions promises a feasible approach to the effective realization of the interaction between light and matter or to the controlled observation of quantum electrodynamics phenomena with many atoms.
Long-range transport of quantum information across a network is most readily achieved through the use of photons as the information carriers. The nodes of such a quantum network are most naturally a quantum memory or information processor, which typically do not rely upon photonic qubits. Realizing a large-scale distributed quantum network therefore requires an efficient interface between the two physical manifestations of the quantum information. The most promising platform for realizing a quantum computer is the manipulation of trapped atomic ions, as this system has demonstrated all the fundamental requirements to realize a quantum computer. Additionally, trapped ions posses long coherence times necessary for quantum memories. The interface between atomic and photonic qubits relies on a high photon emission rate into the collected solid angle. Most methods of photon collection for quantum networks use a high numerical aperture microscope objective, which only collects on the order of 1% of all the emitted photons. This results in a small probability of successfully linking two quantum nodes. In this work, I present the design, simulation, and implementation of a trapped ion cavity QED system capable of improving the photon collection efficiency. A single ytterbium ion is coupled to a high-finesse optical cavity. The photon scatter rate into the cavity mode is enhanced by a factor of 130 over the free-space scatter rate into the cavity solid angle. This represents the first step towards realizing a protocol to entangle the polarization of an emitted photon to the Zeeman sublevels of the ion with high photon collection efficiency. Simulations of the experimental system indicate that with an optical cavity up to 4% of the light emitted by the ion can be collected.