Compact and robust cold atom sources are increasingly important for quantum research, especially for transferring cutting-edge quantum science into practical applications. In this study, we report on a novel scheme that uses a metasurface optical chip to replace the conventional bulky optical elements used to produce a cold atomic ensemble with a single incident laser beam, which is split by the metasurface into multiple beams of the desired polarization states. Atom numbers ~10⁷ and temperatures (about 35 μK) of relevance to quantum sensing are achieved in a compact and robust fashion. Our work highlights the substantial progress toward fully integrated cold atom quantum devices by exploiting metasurface optical chips, which may have great potential in quantum sensing, quantum computing, and other areas.

The recent increasing interest in detecting gravitational waves (GWs) by lunar seismic measurement urges us to have a clear understanding of the response of the moon to passing GWs. In this paper, we clarify the relationship between two seemingly different response functions which have been derived previously using two different methods, one taking the field-theory approach and the other using the tidal force induced by GWs. We revisit their derivation and prove, by both analytical arguments and numerical calculations, that the two response functions are equivalent. Their apparent difference can be attributed to the choice of different coordinates. Using the correct response function, we calculate the sensitivities (to GWs) of several designed lunar seismometers, and find that the sensitivity curves between ${10}^{-3}$ and 0.1 Hz are much flatter than the previous calculations based on normal-mode model. Our results will help clarify the scientific objectives of lunar GW observation, as well as provide important constraints on the design of lunar GW detectors.

Motivated by the old idea of using the Moon as a resonant gravitational wave (GW) detector, as well as the recent updates in modeling the lunar response to GWs, we reevaluate the feasibility of using a network of lunar seismometers to constrain the stochastic GW background (SGWB). In particular, using the updated model of the lunar response, we derive the pattern functions for the two polarizations of GW. With these pattern functions, we further calculate the overlap reduction functions for a network of lunar seismometers, where we have relaxed the conventional assumption that lunar seismometers are perfectly leveled to measure only the vertical acceleration. We apply our calculation to two future lunar projects, namely, Chang’e and the Lunar Gravitational Wave Antenna (LGWA). We find that the two projects could constrain the SGWB to a level of ${\mathrm{\Omega }}_{\mathrm{GW}}^{\text{Chang}’\mathrm{e}}<2.4\times {10}^2$ and ${\mathrm{\Omega }}_{\mathrm{GW}}^{\mathrm{LGWA}}<2.0\times {10}^{-10}$, respectively, which corresponds to a signal-to-noise ratio of $\mathrm{SNR}=3$. These results are better than the constraints placed previously on the SGWB in the mid-frequency band (around ${10}^{-3}–10\mathrm{Hz}$) by various types of experiments.

We briefly review the status of applying quantum squeezing to aid the search for gravitational waves with km-scale laser interferometers operating in the audio frequency band. The target audience is quantum optics professionals who are interested in an easily accessible introduction to the gravitational wave detector, both as an application of squeezing and as a platform for developing other quantum techniques.

Acquiring precise information about the mode content of a laser is critical for multiplexed optical communications, optical imaging with active wave-front control, and quantum-limited interferometric measurements. Hologram-based mode decomposition devices, such as spatial light modulators, allow a fast, direct measurement of the mode content, but they have limited precision due to cross coupling between modes. Here, we report a proof-of-principle demonstration of mode decomposition with a metasurface, resulting in significantly enhanced precision. A mode-weight fluctuation of $6\times {10}^{-7}$ was measured with 1 s of averaging at a Fourier frequency of 80 Hz, an improvement of more than three orders of magnitude compared to the state-of-the-art spatial light modulator decomposition. The improvement is attributable to the reduction in cross coupling enabled by the exceptionally small pixel size of the metasurface. We show a systematic study of the limiting sources of noise, and we show that there is a promising path towards complete mode decomposition with similar precision.