An Estimation Theoretical Characterization of Coherent States

Akio Fujiwara, Hiroshi Nagaoka

We introduce a class of quantum pure state models called the coherent models. A coherent model is an even-dimensional manifold of pure states whose tangent space is characterized by a symplectic structure. In a rigorous framework of noncommutative statistics, it is shown that a coherent model inherits and expands the original spirit of the minimum uncertainty property of coherent states.

Markku P. V. Stenberg, Kevin Pack, Frank K. Wilhelm

Jean-Pierre Antoine, Bagarello, Fabio, Jean‐Pierre Gazeau

Sergey N. Filippov, Vladimir I. Man’ko, A S Coelho +2 more

The travelling modes of single-photon-added coherent states (SPACS) are characterized by using optical homodyne tomography. Given a set of experimentally measured quadrature distributions, we estimate parameters of the state and also extract information about the detector efficiency. The method used is minimal distance estimation between theoretical and experimental quantities, which additionally allows to evaluate the precision of the estimated parameters. Given the experimental data, we also estimate the lower and upper bounds on fidelity. The results are believed to encourage a more precise engineering and detection of SPACS.

Jaromír Fiurášek

We present and theoretically analyze a method for direct estimation of the second-order correlation function $g^{(2)}(0)$ from the click statistics of a multiplexed detector composed of M binary on-off detection channels. The method uses linear estimators of the first and second moments of the photon-number operator and can provide accurate results even for optical fields with substantial mean photon numbers. For a fixed number of channels, the detection range can be extended by introducing additional losses before the detector. We demonstrate the performance of the method for coherent, thermal, amplitude-squeezed, and photon-added coherent states. We also derive a nonclassicality criterion based on the estimated correlation function and show how the method can be adapted to unbalanced detectors. Our work establishes direct estimation of $g^{(2)}(0)$ as a simple and versatile method for quantitatively characterizing quantum light using multiplexed click detectors.

M. V. Jabir, Riley B. Dawkins, Javier Sabines-Chesterking +4 more

Quantum metrology plays a crucial role in characterizing and stabilizing optical channels in a quantum network, where precise estimation of loss is critical for loss-sensitive quantum protocols. Optical fiber channels are the primary medium for linking quantum nodes, where loss estimation with optical quantum states may enhance the precision compared to classical probes. In this study, we investigate the use of two-mode squeezed vacuum (TMSV) states, an optical quantum state generated via parametric down-conversion, and their detection with photon-number-resolving detectors for characterization of transmission loss. Theoretical analysis indicates that TMSV states exhibit higher Fisher information for transmission parameter estimation than coherent states, suggesting they are superior probes that can significantly enhance measurement precision. Our experimental results confirm that these TMSV states outperform coherent states in the context of loss estimation in an optical channel, achieving up to 3.9 dB higher Fisher information for transmissivity estimation without relying on post-selection measurements. This source can effectively probe transmission losses in optical fibers up to 35 km, maintaining a measurement precision advantage over coherent probe states. These findings underscore the potential of TMSV states to advance quantum metrology and improve the robustness of quantum network applications.