Single-Pixel Imaging with Heralded Single Photons

Traditional remote sensing applications are often based on pulsed laser illumination with a narrow linewidth and characteristic repetition rate, which are not conducive to covert operation. Whatever methods are employed for covert sensing, a key requirement is for the probe light to be indistinguishable from background illumination. We present a method to perform single-pixel imaging that suppresses the effect of background light and hence improves the signal-to-noise ratio by using correlated photon-pairs produced via spontaneous parametric down conversion. One of the photons in the pair is used to illuminate the object whilst the other acts as a temporal reference, allowing the signal photons to be distinguished from background noise. This heralding method shows how the noise regime is key to producing higher contrast images.

Psycho-Emotional Impact of Anomaly Ultrasound Scan in Romanian Pregnant Women

Objective: Second-trimester anomaly scan was introduced as a regulated practice in Romania in 2019, causing misperceptions and unrealistic expectations about this examination among pregnant women. This study aimed to assess whether second trimester anomaly scan is a reason “per se” for maternal anxiety. Design: A prospective type 1 cohort study was conducted in a tertiary prenatal diagnosis center with three locations in Bucharest, Romania, among pregnant women who underwent a second trimester anomaly scan between 1 December 2019 and 29 February 2020. Main outcome measure: Anxiety at the time of prenatal anomaly scan. Results: Out of the 138 participants, 32.6% believed that the anomaly scan could detect all fetus defects, 13.8% considered that the baby is bothered by the probe “light”, 8.7% believed that the scan could harm the fetus, 96.4% reported that it was a pleasant experience, and 95% felt that it strengthened their bond with the fetus. The State-Trait Anxiety Inventory (STAI) score revealed that women with high state anxiety were more anxious at pre-scan (p = 0.001). Conclusion: Ultrasound scan in the second trimester is correlated with a significant anxiety for women who are prone to this psychological trait. It is also a good opportunity to screen for highly anxious women who could benefit from prenatal psychological counseling to facilitate timely recognition and prevention of postpartum psychiatric disorders such as depression.

Spontaneous decay-induced quantum dynamics in Rydberg-blockaded Λ-type atoms

Strongly Rydberg-blockaded two-level atoms form a Rydberg superatom which is excited only to a collective symmetrical Dicke state. However, emerging often in the alkali-earth atoms, spontaneous decay from the Rydberg state to an additional pooling state renders the ensemble no longer a closed superatom. Herein we present a computationally efficient model to characterize the interaction between a fully Rydberg-blockaded ensemble of N Λ-type three-level atoms and a strong probe light field in a coherent state. The model enables us to achieve a decomposition of the coupled dynamics in the strong field limit, which significantly reduces the complexity of computing the N-body system evolution and paves the way for practical analysis in experiments. A quasi-steady-state power spectrum with multiple sidebands is found in the scattered field. The relative heights of the sidebands show a time-dependence determined by the atomic relaxation, which illuminates potential applications of using the system in information transfer of quantum networks. With negligible dissipative flipping to the unsymmetrical states, the atomic relaxation time, indicating a linearly increasing pooling state fraction, is derived analytically as a function of the number of atoms.

All-Optical Non-Inverted Parity Generator and Checker Based on Semiconductor Optical Amplifiers

An all-optical non-inverted parity generator and checker based on semiconductor optical amplifiers (SOAs) are proposed with four-wave mixing (FWM) and cross-gain modulation (XGM) non-linear effects. A 2-bit parity generator and checker using by exclusive NOR (XNOR) and exclusive OR (XOR) gates are implemented by first SOA and second SOA with 10 Gb/s return-to-zero (RZ) code, respectively. The parity and check bits are provided by adjusting the center wavelength of the tunable optical bandpass filter (TOBPF). A saturable absorber (SA) is used to reduce the negative effect of small signal clock (Clk) probe light to improve extinction ratio (ER) and optical signal-to-noise ratio (OSNR). For Pe and Ce (even parity bit and even check bit) without Clk probe light, ER and OSNR still maintain good performance because of the amplified effect of SOA. For Po (odd parity bit), ER and OSNR are improved to 1 dB difference for the original value. For Co (odd check bit), ER is deteriorated by 4 dB without SA, while OSNR is deteriorated by 12 dB. ER and OSNR are improved by about 2 dB for the original value with the SA. This design has the advantages of simple structure and great integration capability and low cost.

Acquiring the large phase jumping beyond pi with phase unwrapping assisted by auxiliary light in PHI-OTDR

The absolute difference (phase jumping) between two adjacent phases should be less than pi in order to accurately recover the phase signal with traditional phase unwrapping algorithm, which limits the capability of quantitative measurement for traditional PHI-OTDR. In this article, a new process of phase unwrapping with an auxiliary light in coherent PHI-OTDR is proposed, so the resolvable phase jumping is extended to a larger value beyond pi and the capability of phase unwrapping is improved. In this PHI-OTDR system, wrapped differential phases between a reference position and the subsequent positions of fiber are firstly acquired for all probe light pulses. And wrapped differential phases of interleaving pulse sequence are unwrapped using the traditional phase unwrapping algorithm. Then, positions where the differential phases are correctly unwrapped are obtained from the discontinuously linear profile of the phase change curves of the original probe light. Based on these positions, the information of perturbation can be correctly retrieved. In experiment, the new process of phase unwrapping with the auxiliary for PHI-OTDR is executed and a perturbation signal which induces a maximum phase jumping of 3.7154 rad is well reconstructed. More experimental results all demonstrate the validity of the proposed method.

Acquiring the large phase jumping beyond pi with phase unwrapping assisted by auxiliary light in PHI-OTDR

The absolute difference (phase jumping) between two adjacent phases should be less than pi in order to accurately recover the phase signal with traditional phase unwrapping algorithm, which limits the capability of quantitative measurement for traditional PHI-OTDR. In this article, a new process of phase unwrapping with an auxiliary light in coherent PHI-OTDR is proposed, so the resolvable phase jumping is extended to a larger value beyond pi and the capability of phase unwrapping is improved. In this PHI-OTDR system, wrapped differential phases between a reference position and the subsequent positions of fiber are firstly acquired for all probe light pulses. And wrapped differential phases of interleaving pulse sequence are unwrapped using the traditional phase unwrapping algorithm. Then, positions where the differential phases are correctly unwrapped are obtained from the discontinuously linear profile of the phase change curves of the original probe light. Based on these positions, the information of perturbation can be correctly retrieved. In experiment, the new process of phase unwrapping with the auxiliary for PHI-OTDR is executed and a perturbation signal which induces a maximum phase jumping of 3.7154 rad is well reconstructed. More experimental results all demonstrate the validity of the proposed method.

Resonant scattering-enhanced photothermal microscopy

We have developed a novel strategy of resonant scattering-enhanced photothermal microscopy, where the imaged nanoparticles are near-resonant with the probe light.