Quantum parameter estimation is a crucial tool for inferring unknown parameters in physical models from experimental data. The Jaynes–Cummings model is a widely used model in quantum optics that describes the interaction between an atom and a single-mode quantum optical field. In this Letter, we systematically investigate the problem of estimating the atom-light coupling strength in this model and optimize the initial state in the full Hilbert space. We compare the precision limits achievable for different optical field quantum states, including coherent states, amplitude- and phase-squeezed states, and provide experimental suggestions with an easily prepared substitute for the optimal state. Our results provide valuable insights into optimizing quantum parameter estimation in the Jaynes–Cummings model and can have practical implications for quantum metrology with hybrid quantum systems.

Photon number-squeezed states are of significant value in fundamental quantum research and have a wide range of applications in quantum metrology. Most of their preparation mechanisms require precise control of quantum dynamics and are less tolerant to dissipation. We propose a mechanism that is not subject to these restraints. In contrast to common approaches, we exploit the self-balancing between two types of dissipation induced by positive- and negative-temperature reservoirs to generate steady states with sub-Poissonian statistical distributions of photon numbers. We also show how to implement this mechanism with cavity optomechanical systems. The quality of the prepared photon number-squeezed state is estimated by our theoretical model combined with realistic parameters for various typical optomechanical systems.

The accelerometer plays a crucial role in inertial navigation. The performance of conventional accelerometers such as lasers is usually limited by the sensing elements and shot noise limitation (SNL). Here, we propose an advanced development of an accelerometer based on atom–light quantum correlation, which is composed of a cold atomic ensemble, light beams, and an atomic vapor cell. The cold atomic ensemble, prepared in a magneto-optical trap and free-falling in a vacuum chamber, interacts with light beams to generate atom–light quantum correlation. The atomic vapor cell is used as both a memory element storing the correlated photons emitted from cold atoms and a bandwidth controller through the control of free evolution time. Instead of using a conventional sensing element, the proposed accelerometer employs interference between quantum-correlated atoms and light to measure acceleration. Sensitivity below SNL can be achieved due to atom–light quantum correlation, even in the presence of optical loss and atomic decoherence. Sensitivity can be achieved at the ng/Hz level, based on evaluation via practical experimental conditions. The present design has a number of significant advantages over conventional accelerometers such as SNL-broken sensitivity, broad bandwidth from a few hundred Hz to near MHz, and avoidance of the technical restrictions of conventional sensing elements.

Quantum non-demolition (QND) measurement is an important tool in the fields of quantum information processing and quantum optics. The atom-light hybrid interferometer is of great interest due to its combination of an atomic spin wave and an optical wave, which can be utilized for photon number QND measurement via the AC-Stark effect. In this paper, we present an SU(1,1)-SU(2)-concatenated atom-light hybrid interferometer, and theoretically study QND measurement of the photon number. Compared to the traditional SU(2) interferometer, the signal-to-noise ratio in a balanced case is improved by a gain factor of the nonlinear Raman process (NRP) in this proposed interferometer. Furthermore, the condition of high-quality QND measurement is analyzed. In the presence of losses, the measurement quality is reduced. We can adjust the gain parameter of the NRP in the readout stage to reduce the impact due to losses. Moreover, this scheme is a multiarm interferometer, which has the potential of multiparameter estimation with many important applications in the detection of vector fields, quantum imaging, and so on.