Single-particle interferometers became a remarkable tool in many fields of fundamental research and technical applications, such as sensor technology. Due to their high phase sensitivity, these interferometers are susceptible to dephasing which originates typically from electromagnetic fields, mechanical vibrations or temperature drifts, leading to a reduced contrast in the spatial signal. In opposition to decoherence, where the contrast is reduced due to the entanglement of the quantum state to the environment, dephasing is a collective phase shift of the interference pattern. Therefore, it can in principle be reversed after the measurement if the spatial and temporal information about the particle events in the detection plane is available. Using two-particle correlations, it is possible to reveal the properties of the unperturbed interference pattern, such as contrast and spatial periodicity, and the dephasing characteristics. In this thesis, the second-order correlation analysis of multifrequency dephasing is discussed theoretically and demonstrated experimentally. The second-order correlation theory is derived and the equations are explained in detail. Additionally, the numerical correlation function used to extract the experimental data is provided and it is explained how the discretization influences the accuracy of the obtained parameters. Using an electron biprism interferometer, the validity of our correlation analysis is verified experimentally by applying artificially an external time-varying magnetic field dephasing the temporally integrated interference pattern. It is demonstrated successfully that the parameters of the unperturbed interference pattern can be revealed even if the contrast in the spatial signal is nearly vanished. Furthermore, the characteristics of single- and multifrequency dephasing can be identified and used for the reconstruction of the unperturbed interference pattern. The applicability of our correlation analysis is also investigated by applying external mechanical vibrations in a broad frequency range to the electron biprism interferometer. Here, the amplitude spectrum of the correlation function is used together with a numerical algorithm to identify the unknown dephasing frequencies, amplitudes, and phases. In this way, the vibrational response spectrum of the biprism interferometer including the mechanical resonances could be determined. Our correlation analysis can be applied in principle in all interferometers generating a spatial interference pattern on a detector with high spatial and temporal single-particle resolution. Such detectors are available for electrons, ions, atoms, neutrons, molecules, and photons which enables the application of our method in a wide range of interferometric experiments. In fundamental research, the second-order correlation analysis can be used to distinguish between dephasing and decoherence in experiments where the contrast of the interference pattern has to be determined. This is e.g. relevant for studying the mechanisms of decoherence and testing the limits of quantum mechanical superposition. Our method can also be a useful tool in technical applications to optimize the electromagnetic shielding and vibrational damping of the interferometer by measuring its response spectra. As the correlation analysis is suitable to identify unknown dephasing frequencies and the corresponding amplitudes, it can be applied in sensor technology. At the end of this thesis, a compact sensor for the measurement of time-varying electromagnetic fields based on an electron biprism interferometer is proposed. Due to the wide application possibilities of the described correlation analysis, it is of significant relevance in various fields of single-particle interferometry.Single-particle interferometers became a remarkable tool in many fields of fundamental research and technical applications, such as sensor technology. Due to their high phase sensitivity, these interferometers are susceptible to dephasing which originates typically from electromagnetic fields, mechanical vibrations or temperature drifts, leading to a reduced contrast in the spatial signal. In opposition to decoherence, where the contrast is reduced due to the entanglement of the quantum state to the environment, dephasing is a collective phase shift of the interference pattern. Therefore, it can in principle be reversed after the measurement if the spatial and temporal information about the particle events in the detection plane is available. Using two-particle correlations, it is possible to reveal the properties of the unperturbed interference pattern, such as contrast and spatial periodicity, and the dephasing characteristics. In this thesis, the second-order correlation analysis of multifrequency dephasing is discussed theoretically and demonstrated experimentally. The second-order correlation theory is derived and the equations are explained in detail. Additionally, the numerical correlation function used to extract the experimental data is provided and it is explained how the discretization influences the accuracy of the obtained parameters. Using an electron biprism interferometer, the validity of our correlation analysis is verified experimentally by applying artificially an external time-varying magnetic field dephasing the temporally integrated interference pattern. It is demonstrated successfully that the parameters of the unperturbed interference pattern can be revealed even if the contrast in the spatial signal is nearly vanished. Furthermore, the characteristics of single- and multifrequency dephasing can be identified and used for the reconstruction of the unperturbed interference pattern. The applicability of our correlation analysis is also investigated by applying external mechanical vibrations in a broad frequency range to the electron biprism interferometer. Here, the amplitude spectrum of the correlation function is used together with a numerical algorithm to identify the unknown dephasing frequencies, amplitudes, and phases. In this way, the vibrational response spectrum of the biprism interferometer including the mechanical resonances could be determined. Our correlation analysis can be applied in principle in all interferometers generating a spatial interference pattern on a detector with high spatial and temporal single-particle resolution. Such detectors are available for electrons, ions, atoms, neutrons, molecules, and photons which enables the application of our method in a wide range of interferometric experiments. In fundamental research, the second-order correlation analysis can be used to distinguish between dephasing and decoherence in experiments where the contrast of the interference pattern has to be determined. This is e.g. relevant for studying the mechanisms of decoherence and testing the limits of quantum mechanical superposition. Our method can also be a useful tool in technical applications to optimize the electromagnetic shielding and vibrational damping of the interferometer by measuring its response spectra. As the correlation analysis is suitable to identify unknown dephasing frequencies and the corresponding amplitudes, it can be applied in sensor technology. At the end of this thesis, a compact sensor for the measurement of time-varying electromagnetic fields based on an electron biprism interferometer is proposed. Due to the wide application possibilities of the described correlation analysis, it is of significant relevance in various fields of single-particle interferometry.

Jan 1, 20180 citations

Two-particle interferometry

Michael Horne, Abner Shimony, Anton Zeilinger

NatureOct 1, 199027 citations

Locality and nonlocality in correlated two-particle interferometry

Mai Mai Lam, Christopher Dewdney

Physics Letters ANov 1, 199020 citations

Threshold in Quantum Correlated Interference for a Particle Interacting with Two Scatterers

Frank V. Kowalski

Abstract Correlated interference is calculated for a microscopic particle retro‐reflecting from two spatially separated scatterers that are free to move, all three of which are treated as quantum bodies: the positions of the particle traversing this 1D interferometer and those of the interferometer components are all uncertain. Interference in a measurement of only the particle is shown to disappear for microscopic yet appear for mesoscopic scatterers, contrary to that of a quantum‐classical transition. A measurement of this threshold can verify quantum correlations in many‐body systems by measuring only the retro‐reflected microscopic particle. The decoherence of a mesoscopic scatterer is determined by this threshold without it having to traverse slits or beamsplitters.Abstract Correlated interference is calculated for a microscopic particle retro‐reflecting from two spatially separated scatterers that are free to move, all three of which are treated as quantum bodies: the positions of the particle traversing this 1D interferometer and those of the interferometer components are all uncertain. Interference in a measurement of only the particle is shown to disappear for microscopic yet appear for mesoscopic scatterers, contrary to that of a quantum‐classical transition. A measurement of this threshold can verify quantum correlations in many‐body systems by measuring only the retro‐reflected microscopic particle. The decoherence of a mesoscopic scatterer is determined by this threshold without it having to traverse slits or beamsplitters.

arXiv:2408.07473Annalen der PhysikJan 17, 20222 citations

Introduction to Two-Particle Interferometry

Michael Horne, Abner Shimony, Anton Zeilinger

NATO ASI series. Series B : PhysicsJan 1, 199019 citations

Coherent collisional decoherence

Leonardo Badurina, Clara Murgui, Ryan Plestid

We study the decoherence of a system of $N$ noninteracting heavy particles (atoms) due to coherent scattering with a background gas. We introduce a framework for computing the induced phase shift and loss of contrast for arbitrary preparations of $N$ -particle quantum states. We find phase shifts that are inherently $(N\ensuremath{\ge}2)$-body effects and may be searched for in future experiments. We analyze simple setups, including a two-mode approximation of an interferometer. We study fully entangled $N00N$ states, which resemble the correlated positions in a matter interferometer, as well as totally uncorrelated product states that are representative of a typical state in an atom interferometer. We find that the extent to which coherent enhancements increase the rate of decoherence depends on the observable of interest, state preparation, and details of the experimental design. In the context of future ultralow-recoil (e.g., light dark matter) searches with atom interferometers we conclude that (i) there exists a coherently enhanced scattering phase which can be searched for using standard (i.e., contrast/visibility and phase) interferometer observables; (ii) although decoherence rates of one-body observables are not coherently enhanced, a coherently enhanced loss of contrast can still arise from dephasing; and (iii) higher statistical moments (which are immediately accessible in a counting experiment) are coherently enhanced and may offer a new tool with which to probe the soft scattering of otherwise undetectable particles in the laboratory.We study the decoherence of a system of $N$ noninteracting heavy particles (atoms) due to coherent scattering with a background gas. We introduce a framework for computing the induced phase shift and loss of contrast for arbitrary preparations of $N$-particle quantum states. We find phase shifts that are inherently $(N\ensuremath{\ge}2)$-body effects and may be searched for in future experiments. We analyze simple setups, including a two-mode approximation of an interferometer. We study fully entangled $N00N$ states, which resemble the correlated positions in a matter interferometer, as well as totally uncorrelated product states that are representative of a typical state in an atom interferometer. We find that the extent to which coherent enhancements increase the rate of decoherence depends on the observable of interest, state preparation, and details of the experimental design. In the context of future ultralow-recoil (e.g., light dark matter) searches with atom interferometers we conclude that (i) there exists a coherently enhanced scattering phase which can be searched for using standard (i.e., contrast/visibility and phase) interferometer observables; (ii) although decoherence rates of one-body observables are not coherently enhanced, a coherently enhanced loss of contrast can still arise from dephasing; and (iii) higher statistical moments (which are immediately accessible in a counting experiment) are coherently enhanced and may offer a new tool with which to probe the soft scattering of otherwise undetectable particles in the laboratory.

arXiv:2402.03421Physical Review ASep 10, 20247 citations

We study the decoherence of a system of

N

noninteracting heavy particles (atoms) due to coherent scattering with a background gas. We introduce a framework for computing the induced phase shift and loss of contrast for arbitrary preparations of

N

-particle quantum states. We find phase shifts that are inherently $(N\ensuremath{\ge}2)$-body effects and may be searched for in future experiments. We analyze simple setups, including a two-mode approximation of an interferometer. We study fully entangled

N00N

states, which resemble the correlated positions in a matter interferometer, as well as totally uncorrelated product states that are representative of a typical state in an atom interferometer. We find that the extent to which coherent enhancements increase the rate of decoherence depends on the observable of interest, state preparation, and details of the experimental design. In the context of future ultralow-recoil (e.g., light dark matter) searches with atom interferometers we conclude that (i) there exists a coherently enhanced scattering phase which can be searched for using standard (i.e., contrast/visibility and phase) interferometer observables; (ii) although decoherence rates of one-body observables are not coherently enhanced, a coherently enhanced loss of contrast can still arise from dephasing; and (iii) higher statistical moments (which are immediately accessible in a counting experiment) are coherently enhanced and may offer a new tool with which to probe the soft scattering of otherwise undetectable particles in the laboratory.