Stokes parameters are a standard tool in quantum optics. They involve averaged intensities at exits of polarizers. If the overall measured intensity fluctuates, as, e.g., for states with undefined photon numbers, the instances of its increased value contribute more to the parameters. One can introduce normalized quantum Stokes operators. Operationally, for a given single run of the experiment, their values are differences of measured intensities (or photon numbers) at the two exits of a polarizer divided by their sum. Effects of intensity fluctuations are removed. Switching to normalized Stokes operators results in more sensitive entanglement conditions. We also show a general method of deriving an entanglement indicator for optical fields which use polarization correlations, which starts with any two-qubit entanglement witness. This allows one to vastly expand the family of such indicators.Stokes parameters are a standard tool in quantum optics. They involve averaged intensities at exits of polarizers. If the overall measured intensity fluctuates, as, e.g., for states with undefined photon numbers, the instances of its increased value contribute more to the parameters. One can introduce normalized quantum Stokes operators. Operationally, for a given single run of the experiment, their values are differences of measured intensities (or photon numbers) at the two exits of a polarizer divided by their sum. Effects of intensity fluctuations are removed. Switching to normalized Stokes operators results in more sensitive entanglement conditions. We also show a general method of deriving an entanglement indicator for optical fields which use polarization correlations, which starts with any two-qubit entanglement witness. This allows one to vastly expand the family of such indicators.

arXiv:1508.02368Physical Review AApr 10, 201716 citations

Collisional relaxation of the 6s[3/2 ]10 and 6s’[1/2 ]10 mJ levels of xenon using resonantly enhanced multiphoton ionization

Dimitrios Charalambidis, A. Lyras, P. Lambropoulos +3 more

Collisional relaxation of the 6s ${[3/2]}_{1}^{0}$ and 6s' ${[1/2]}_{1}^{0}$ ${m}_{J}$ levels of Xe has been investigated both experimentally and theoretically. Collisional disalignment and dephasing of the ${m}_{J}$ levels have been studied by measuring the pressure and laser intensity dependence of the ratio of the ionization from selectively excited ${m}_{J}$ =0 and \ifmmode\pm\else\textpm\fi{}1 sublevels in a three-photon resonant-ionization experiment via the 6s and 6s' states of Xe. The selective ionization is achieved by a novel use of two counterpropagating laser beams having parallel and orthogonal polarization, respectively. The pressure dependence of the ionization ratio has been calculated by solving a system of rate equations derived from a full set of density-matrix equations pertaining to the particular experimental conditions. Collisional-relaxation cross sections of the investigated levels have been estimated by fitting the calculated results to the experimental data. The ionization ratio is found to be sensitive to both disalignment and dephasing of the ${m}_{J}$ levels.Collisional relaxation of the 6s${[3/2]}_{1}^{0}$ and 6s'${[1/2]}_{1}^{0}$ ${m}_{J}$ levels of Xe has been investigated both experimentally and theoretically. Collisional disalignment and dephasing of the ${m}_{J}$ levels have been studied by measuring the pressure and laser intensity dependence of the ratio of the ionization from selectively excited ${m}_{J}$=0 and \ifmmode\pm\else\textpm\fi{}1 sublevels in a three-photon resonant-ionization experiment via the 6s and 6s' states of Xe. The selective ionization is achieved by a novel use of two counterpropagating laser beams having parallel and orthogonal polarization, respectively. The pressure dependence of the ionization ratio has been calculated by solving a system of rate equations derived from a full set of density-matrix equations pertaining to the particular experimental conditions. Collisional-relaxation cross sections of the investigated levels have been estimated by fitting the calculated results to the experimental data. The ionization ratio is found to be sensitive to both disalignment and dephasing of the ${m}_{J}$ levels.

Physical Review AFeb 1, 19907 citations

Ultra-sensitive measurement of small optical rotation angles using quantum entanglement based on a quasi-Wollaston prism beam splitter

Shuai Wang, Jing Zhu, Lianqing Zhu

The measurement of optical rotation is fundamental to optical atomic magnetometry. Ultra-high sensitivity has been achieved by employing a quasi-Wollaston prism as the beam splitter within a quantum entanglement state, complemented by synchronous detection. Initially, we designed a quasi-Wollaston prism and intentionally rotated the crystal axis of the exit prism element by a specific bias angle. A linearly polarized light beam, incident upon this prism, is divided into three beams, with the intensity of each beam correlated through quantum entanglement. Subsequently, we formulated the equations for optical rotation angles by synchronously detecting the intensities of these beams, distinguishing between differential and reference signals. Theoretical analysis indicates that the measurement uncertainty for optical rotation angles, when using quantum entanglement, exceeds the conventional photon shot noise limit. Moreover, we have experimentally validated the effectiveness of our method. In DC mode, the experimental results reveal that the measurement uncertainty for optical rotation angles is 4.7 × 10 −9 rad, implying a sensitivity of 4.7 × 10 −10 rad/Hz 1/2 for each 0.01 s measurement duration. In light intensity modulation mode, the uncertainty is 48.9 × 10 −9 rad, indicating a sensitivity of 4.89 × 10 −9 rad/Hz 1/2 per 0.01 s measurement duration. This study presents a novel approach for measuring small optical rotation angles with unprecedentedly low uncertainty and high sensitivity, potentially playing a pivotal role in advancing all-optical atomic magnetometers and magneto-optical effect research.The measurement of optical rotation is fundamental to optical atomic magnetometry. Ultra-high sensitivity has been achieved by employing a quasi-Wollaston prism as the beam splitter within a quantum entanglement state, complemented by synchronous detection. Initially, we designed a quasi-Wollaston prism and intentionally rotated the crystal axis of the exit prism element by a specific bias angle. A linearly polarized light beam, incident upon this prism, is divided into three beams, with the intensity of each beam correlated through quantum entanglement. Subsequently, we formulated the equations for optical rotation angles by synchronously detecting the intensities of these beams, distinguishing between differential and reference signals. Theoretical analysis indicates that the measurement uncertainty for optical rotation angles, when using quantum entanglement, exceeds the conventional photon shot noise limit. Moreover, we have experimentally validated the effectiveness of our method. In DC mode, the experimental results reveal that the measurement uncertainty for optical rotation angles is 4.7 × 10 −9 rad, implying a sensitivity of 4.7 × 10 −10 rad/Hz 1/2 for each 0.01 s measurement duration. In light intensity modulation mode, the uncertainty is 48.9 × 10 −9 rad, indicating a sensitivity of 4.89 × 10 −9 rad/Hz 1/2 per 0.01 s measurement duration. This study presents a novel approach for measuring small optical rotation angles with unprecedentedly low uncertainty and high sensitivity, potentially playing a pivotal role in advancing all-optical atomic magnetometers and magneto-optical effect research.

Optics ExpressMay 1, 20241 citation

Rotation of polarization of a multiphoton state

Fang‐Wen Sun, Bi‐Heng Liu, Yun‐Feng Huang +2 more

Physics Letters AJan 7, 20062 citations

Collisional relaxation of the 6s

{[3/2]}_{1}^{0}

and 6s'

{[1/2]}_{1}^{0}

{m}_{J}

levels of Xe has been investigated both experimentally and theoretically. Collisional disalignment and dephasing of the

{m}_{J}

levels have been studied by measuring the pressure and laser intensity dependence of the ratio of the ionization from selectively excited

{m}_{J}

=0 and \ifmmode\pm\else\textpm\fi{}1 sublevels in a three-photon resonant-ionization experiment via the 6s and 6s' states of Xe. The selective ionization is achieved by a novel use of two counterpropagating laser beams having parallel and orthogonal polarization, respectively. The pressure dependence of the ionization ratio has been calculated by solving a system of rate equations derived from a full set of density-matrix equations pertaining to the particular experimental conditions. Collisional-relaxation cross sections of the investigated levels have been estimated by fitting the calculated results to the experimental data. The ionization ratio is found to be sensitive to both disalignment and dephasing of the

{m}_{J}

levels.