Kui Liu

Quantum metrology can beat the shot-noise limit (SNL) with nonclassical resources, yet simultaneously realizing sub-Rayleigh resolution and sub-SNL sensitivity in a deployable interferometer remains challenging. Here we experimentally validate a deterministic phase-measurement protocol that combines single-port balanced homodyne detection in a Mach-Zehnder interferometer with ternary-binning post-processing. For a coherent probe with a mean photon number of about 67, ternary binning preserves sub-Rayleigh resolution while mitigating the near-zero-phase ill-conditioning of binary-binning readout, yielding a 7.15-fold resolution enhancement relative to the unprocessed interferometer. With 5.99 ± 0.13 dB squeezed-state injection into the vacuum port, the resolution enhancement increases to 13.69-fold, and sub-SNL sensitivity is achieved; the minimum sensitivity improves by a factor of 1.78 compared with the coherent probe. The protocol is deterministic and experimentally accessible, offering a practical route to multiparameter estimation and quantum-enhanced microscopy.

Quantum steering, as a fundamental resource in quantum information science, is a key resource for secure quantum communication networks. Coherent feedback control (CFC) has been widely used to enhance squeezing. In this paper, we utilize a variable beam splitter (VBS) with a reflectivity of k as the feedback controller to build a coherent feedback control system in four-wave mixing (FWM) processes with a spatially structured pump (SSP). We investigate the influence of feedback strength and interaction intensity on quantum steering across different modes under specific phase delay conditions. The results show that the coherent feedback control system can flexibly control quantum steering. By adjusting the parameters, we can achieve various quantum steering types, especially collective multipartite steering and genuine multipartite steering. It has significant practical application value for secure quantum information processing and offers a theoretical reference for the construction of large-scale, secure quantum networks.

Aided by quantum sources, quantum metrology helps enhance measurement precision. Here, we construct a theoretical model for quantum imaging based on squeezed states and present the corresponding numerical results. Through discretization and quantum Fisher information theory, we investigate the two-point resolution and spatial multi-parameter estimation of optical fields with unknown spatial distributions. We calculate and compare imaging results based on squeezed vacuum states, coherent states, and squeezed coherent states; our results show that squeezed coherent states yield greater quantum Fisher information, which can effectively improve imaging quality. In addition, we analyze the influence of imaging basis functions, degree of squeezing, quantum correlations, and other factors on imaging performance. The proposed quantum imaging model and computational method can be extended to more complex scenarios, such as multi-mode squeezed-state imaging schemes and incoherent imaging systems. In the future, this approach is expected to find applications in practical imaging systems, including Raman microscopy and stimulated Brillouin scattering imaging.

Aided by quantum sources, quantum metrology helps enhance measurement precision. Here, we construct a theoretical model for quantum imaging based on squeezed states and present the corresponding numerical results. Through discretization and quantum Fisher information theory, we investigate the two-point resolution and spatial multi-parameter estimation of optical fields with unknown spatial distributions. We calculate and compare imaging results based on squeezed vacuum states, coherent states, and squeezed coherent states; our results show that squeezed coherent states yield greater quantum Fisher information, which can effectively improve imaging quality. In addition, we analyze the influence of imaging basis functions, degree of squeezing, quantum correlations, and other factors on imaging performance. The proposed quantum imaging model and computational method can be extended to more complex scenarios, such as multi-mode squeezed-state imaging schemes and incoherent imaging systems. In the future, it is expected to find applications in practical imaging systems, including Raman microscopy and stimulated Brillouin scattering imaging.

Femtosecond optical vortices feature helical phase fronts within their transverse modes and also display a fixed phase difference among the longitudinal modes. This multi‐dimensional manipulation of femtosecond laser pulses forms a fundamental basis for various applications. While multiple techniques exist for generating traditional femtosecond optical vortices, a notable void persists in the domain of continuous‐variable entanglement. This letter introduces the demonstration of femtosecond optical vortices entanglement accomplished through the synchronously pumped optical parametric oscillator, which is designed with a nonplanar ring cavity to compensate for astigmatism without introducing additional dispersion. The generated light field exhibits both temporal multimode structures, manifested as supermodes in the femtosecond optical frequency comb, and spatial multimode structures carrying orbital angular momentum. Orbital angular momentum entanglement is clearly observed in the first three‐order supermodes. The femtosecond optical vortices entanglement, serving as a precursor of potential, holds the crucial key to unlocking enhanced capabilities in advanced information processing, securing quantum communication, and even paving the way for the realization of multi‐parameter quantum metrology.

Squeezed light is a fundamental nonclassical resource in quantum optics, and considerable progress has been made in its generation and manipulation. Here, we experimentally demonstrate a compact higher-order spatial modes squeezed light source, achieved by integrating second-harmonic generation and optical parametric oscillation within a single doubly resonant cavity. The HG _{2 m ,2 n} pump field, which is essential for the generation of HG _{m , n} mode squeezed states, is produced via internal second-harmonic generation, substantially enhancing both the conversion efficiency and mode purity. With this configuration, we successfully generated squeezed vacuum states in the HG _0,0 , HG _1,0 , and HG _2,0 modes, achieving squeezing levels of −4.53 ± 0.26 dB, −3.68 ± 0.19 dB, and −2.58 ± 0.08 dB, respectively. This platform provides a viable pathway for scalable, multimode quantum state generation, with broad potential in quantum metrology and quantum communication.

We propose two schemes for estimating the separation of two thermal sources via double homodyne and double array homodyne detection considering the joint measurement of conjugate quadratures of the image plane field.By using the Cramér–Rao bound, we demonstrate that the two schemes can estimate the separation well below the Rayleigh limit and have an advantage over direct imaging when the average photon number per source exceeds five.For arbitrary source strengths, double homodyne detection is superior to homodyne detection when the separation is above 2^5/4σ/N _s , σ is the beam width, N _s is the average photon number per source.A larger separation can be estimated better via double array homodyne detection with the superiority of flexible operation compared with other schemes. High-speed and high-efficiency detection enables the measurement schemes with potential practical applications in fluorescence microscopy, astronomy and quantum imaging.

Optical spin–orbit coupling is an important phenomenon and has fruitful applications. Here, we investigate the spin–orbit total angular momentum entanglement in the optical parametric downconversion process. Four pairs of entangled vector vortex modes are experimentally generated directly using a dispersion- and astigmatism-compensated single optical parametric oscillator, and for the first time, to the best of our knowledge, the spin–orbit quantum states are characterized on the quantum higher-order Poincaré sphere, and the relationship of spin–orbit total angular momentum Stokes entanglement is demonstrated. These states have potential applications in high-dimensional quantum communication and multiparameter measurement.

This publisher’s note corrects the authorship in Photon. Res. 10, 2828 (2022)PRHEIZ 2327-9125 10.1364/PRJ.469340 .