Advanced quantum technologies最新文献

In this study, the influence of the nonlinear magneto–optical rotation effect on a spin-exchange relaxation-free (SERF) atomic magnetometer is analyzed. The nonlinear effect is described by saturation parameters obtained from the density matrix model considering the Rabi oscillation of the probe light. For better sensitivity, the nonlinear effect is suppressed, and larger output signals are achieved. Based on the nonlinear effect analysis, the relationship between the probe sensitivity and light power density is obtained, and the optimal probe light power density is measured with best probe sensitivity. The best probe sensitivity improves by ≈6 times at the optimal probe light power density compared with that in the conventional linear optical rotation detection. The proposed method can be applied to SERF magnetometers, co-magnetometers, and atomic spin gyroscopes.

Polarization moments play a crucial role in measuring magnetic fields for nonlinear magneto-optical rotation (NMOR) atomic magnetometers. However, it is challenging to distinguish between each polarization moment and evaluate its effect on the magnetic resonance response signal in an alkali vapor cell with buffer gas. To address this issue, a method is proposed to identify different polarization moments through the frequency shift of the magnetic resonance response signal. The proportion of each polarization moment is determined, and it is demonstrated that the magnetic resonance response signal is affected by the hexadecapole moment, resulting in a frequency shift and a decrease in signal amplitude. To mitigate this effect, an approach is investigated to manipulate the polarization moments by flipping the phase of the pump light. Ultimately, a 15.19% increase in response amplitude is achieved in the simulated geomagnetic environment within the magnetic shield barrel. The theory and method presented here provide strong support for the study of the polarization moments in an alkali vapor cell with buffer gas, which potentially enhance the performance of NMOR atomic magnetometers.

Quantum Hall insulators in artificial systems have become a rapidly developing research field in recent years, and have made significant breakthroughs in observing many novel topological phenomena. However, there are few reports about quantum magnon-photon Hall insulators. Here, a scheme is proposed for implementing a 1D cavity magnonics lattice that exhibits quantum magnon-photon Hall insulator behaviors, where each unit cell comprises cavity photons and magnons. By adjusting the system parameters, it is found that not only different energy spectrum structures can be triggered, but also the distribution of the edge states can show the flipping process, which allows the achievement of the multi-channel topological quantum state transmission. In addition, considering the presence of defects, dissipation, and disorder, it is found that appropriate defects can trigger new topological phases, while dissipation only causes shifts in energy levels without changing the position and period of edge states, and disorder leads to shifts in band structures and edge states, thus demonstrating the robustness of edge states. This work offers an effective way to study topological magnon-photon Hall insulators, which will have promising applications in magnon-based quantum information processing.

In the atomic comagnetometer, nuclear spin relaxation is a core parameter that affects the magnetic field suppression ability and stability, and is influenced by various gradient fields. It is necessary to measure and separate the effects of different gradients on nuclear spin, which helps to effectively suppress them separately. This article proposes a periodic optical pumping method for separating and measuring polarization gradient relaxation and magnetic field gradient relaxation, considering the effects of pump light and applied magnetic field. The comprehensive influence model for pump light on transverse nuclear spin relaxation is established, and the measurement steps and parameter selection criteria for the proposed method considering signal decay characteristics are provided. Furthermore, the proportion of various gradient relaxations is quantified. This work provides an evaluation method for gradient relaxation suppression, supporting the improvement of the measurement sensitivity and stability of the atomic comagnetometer.

Depicted is a novel setup for realizing the photon number splitting (PNS) attack with current-day technology, namely, using the single-photon Raman interaction. In article number 2300437, Eliahu Cohen and co-workers analyze the amount of information which the eavesdropper (Eve) can obtain using this physical realization of PNS, concluding that while part of the secret key is at risk when weak coherent states are used, there is still a price for Eve to pay in terms of the induced noise. This stresses the importance of proper countermeasures.

Quantum coherence suffers from environmental influence but the topological feature may not. In article number 2400053, Zu-Jian Ying rigorously shows that the topological feature manifested by the fundamental Jaynes–Cummings model of light–matter interaction is robust against a general non-Hermiticity induced by dissipation and decay rates. The non-Hermiticity only tilts the spin winding plane, while the winding number is preserved. Several revealed properties may be useful for designing topological quantum devices.

This review article focuses on biphoton sources based on the double-$�\Lambda$ spontaneous four-wave mixing (SFWM) process in laser-cooled as well as room-temperature or hot atomic ensembles. These biphoton sources have the advantage of providing stable frequencies, ultranarrow linewidths, and a tunability of the temporal biphoton width of more than one order of magnitude for high-bandwidth applications. Therefore, the generated photons can be efficiently interfaced to, e.g., atomic quantum memories. In contrast, solid-state biphoton sources typically require assistance by an optical cavity to operate at narrow linewidth that limits the tunability of the temporal width of the biphotons. Present state-of-the-art double-$�\Lambda$ SFWM biphoton sources can achieve one of the following results: a spectral linewidth of 50 kHz (290 kHz) or a temporal width of 13 $��\mu �s�$ (580 ns) with cold (hot) atoms, a detection rate of about 7$��\times �{10}^3�$ cps, and a generation rate of $�{10}^7$ cps at a duty cycle of 0.4% or of $�{10}^5$ cps in the steady state. The theoretical background of these biphoton sources, experimental implementations with cold and hot atoms, and progress over the years, will be illustrated.

The discovery of the interface-enhanced superconductivity in the single-layer film of FeSe epitaxially grown on SrTiO₃ substrates has triggered a flurry of activity in the field of superconductivity. It raised the hope to find more conventional high transition temperature (T_c) superconductors that are purely driven by the electron-phonon interaction at ambient pressure. Here the epitaxial growth of the Pb nano-sized islands on SrTiO₃ (001) substrates with the island volumes ranging from 286 to 4945 nm³ is reported by molecular beam epitaxy, followed by systematic scanning tunneling microscopic/spectroscopic (STM/S) investigation. The observed STS gap for the nanoscale islands highly dependent on the volumes of nano-sized islands, can be divided into three regions. By performing a detailed spectroscopic investigation, it is founded that superconductivity in the volume above 3700 nm³ (Region I) has a zero temperature energy gap (Δ(0)) and T_c of 6.8 meV and 9.8 K obtained by BCS fitting, showing the largely-enhanced Δ and slightly-increased T_c by comparing to the bulk Pb (1.4 meV and 7.2 K). As the volume in the range from 1300 to 3700 nm³ (Region II), a large Coulomb gap induced by electron correlation emerged and shows a volume-dependent behavior, suggesting the reduced size can enhance electron correlation in Pb islands. As the volume decreases down to Region III, enhanced electron correlation and Coulomb gap become more dominant and superconductivity is totally suppressed. The experiment reveals that an electron-electron interaction in nano-sized Pb islands can be significantly enhanced by reducing the island sizes and suppresses the superconductivity, thus demonstrates a competition between superconductivity and electron correlation as the volume varies.