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arXiv:2410.09465 · Physical Review Letters

Coherent Control of Photon Correlations in Trapped Ion Crystals

Kratveer Singh, A. Cidrim, Artem Kovalenko, Tuan Pham Minh, Ondřej Čı́p, L. Slodička, Romain Bachelard

Published May 20, 2025• 7 citations
arXivHTMLPDF

Abstract

While the spontaneous emission from independent emitters provides spatially uncorrelated photons-a typical manifestation of quantum randomness, the interference of the coherent scattering leads to a well-defined intensity pattern-a feature described by linear optics. We here demonstrate experimentally how the interplay between the two mechanisms in large systems of quantum emitters leads to spatial variations of photon correlations. The implementation with trapped ion crystals in free space allows us to observe the anticorrelation between photon rates and variance of the photon number distributions in chains of up to 18 ions. For smaller crystals of four ions, the transition from antibunching to bunching and super-Poissonian statistics of the scattered light is reported. For higher numbers of scatterers, the photon statistics still display a strong deviation from the fully incoherent scattering case. Our results illustrate how the interference of coherent scattering, combined with spontaneous emission, provides a control mechanism for the light statistics.

DOI
10.1103/physrevlett.134.203602

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While the spontaneous emission from independent emitters provides spatially uncorrelated photons-a typical manifestation of quantum randomness, the interference of the coherent scattering leads to a well-defined intensity pattern-a feature described by linear optics. We here demonstrate experimentally how the interplay between the two mechanisms in large systems of quantum emitters leads to spatial variations of photon correlations. The implementation with trapped ion crystals in free space allows us to observe the anticorrelation between photon rates and variance of the photon number distributions in chains of up to 18 ions. For smaller crystals of four ions, the transition from antibunching to bunching and super-Poissonian statistics of the scattered light is reported. For higher numbers of scatterers, the photon statistics still display a strong deviation from the fully incoherent scattering case. Our results illustrate how the interference of coherent scattering, combined with spontaneous emission, provides a control mechanism for the light statistics.
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.
The optical interference constitutes a paramount resource in modern physics. At the scale of individual atoms and photons, it is a diverse concept that causes different coherent phenomena. We present the experimental characterization of both coherent and statistical properties of light emitted from ensembles of trapped ions increasing with a number of contributing phase-incoherent independent atomic particles ranging from a single to up to several hundreds. It conclusively demonstrates how super-Poissonian quantum statistics non-trivially arises purely from the finite number of indistinguishable single-photon emitters in the limit of a single detection mode. The achieved new optical emission regime in which these independent atoms contribute coherently to the super-Poissonian statistics provides a new perspective on the emergence of optical coherence at the atomic scale and constitutes a unique toolbox for its generation and control at the most microscopic level.
We investigate the photon statistics of an ensemble of coherently driven non-interacting two-level atoms in the weak driving regime. As it turns out, the system displays unique emission characteristics that are strongly in contrast to the emission of classical oscillating dipoles. By deriving the second-order autocorrelation function, we show that extraordinary two-photon correlations are obtained, ranging from strong antibunching to superbunching. These features are enhanced by disorder in the emitter positions, and the control parameter is the number of excitations in the system. We observe the appearance of bunching and antibunching when the light is scattered by the atoms predominantly coherently, i.e., mimicking classical Rayleigh scattering, whereas thermal photon statistics is obtained when the light is scattered via spontaneous decay, a well-known quantum effect. The underlying mechanism is the interplay between coherent scattering, which exhibits spatial fluctuations due to interference, and dissipation in the form of isotropic spontaneous decay.
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.
Photon indistinguishability constitutes an essential resource in modern physics. At the scale of individual atoms and photons, it is a diverse concept that causes different coherent phenomena. We present the experimental characterization of indistinguishable photons detected in a single mode from a finite and stable ensemble of single-photon emitters: trapped ions. We conclusively observe an increase of second-order correlation and super-Poissonian statistics of these photons with a number of contributing phase-incoherent independent emissions from the atoms, ranging from a single to up to several hundred. This optical emission regime provides insight into the emergence of super-Poissonian light at the atomic scale by photon indistinguishability. It constitutes a unique toolbox for its generation and control at the most microscopic level.
Photon-mediated interactions between atomic systems are the cornerstone of quantum information transfer. They can arise via coupling to a common electromagnetic mode or by quantum interference. This can manifest in cooperative light-matter coupling, yielding collective rate enhancements such as those at the heart of superradiance, or remote entanglement via measurement-induced path erasure. Here, we report coherent control of cooperative emission arising from two distant but indistinguishable solid-state emitters due to path erasure. The primary signature of cooperative emission, the emergence of bunching at zero-delay in an intensity correlation experiment, is used to characterise the indistinguishability of the emitters, their dephasing, and the degree of correlation in the joint system which can be coherently controlled. In a stark departure from a pair of uncorrelated emitters, we observe photon statistics resembling that of a weak coherent state in Hong-Ou-Mandel type interference measurements. Our experiments establish new techniques to control and characterize cooperative behaviour between matter qubits using the full quantum optics toolbox, a key stepping stone on the route to realising large-scale quantum photonic networks.