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The essence of multi-modal fusion lies in exploiting the complementary information inherent in diverse modalities. However, prevalent fusion methods rely on traditional neural architectures and are inadequately equipped to capture the dynamics of interactions across modalities, particularly in presence of complex intra- and inter-modality correlations. Recent advancements in State Space Models (SSMs), notably exemplified by the Mamba model, have emerged as promising contenders. Particularly, its state evolving process implies stronger modality fusion paradigm, making multi-modal fusion on SSMs an appealing direction. However, fusing multiple modalities is challenging for SSMs due to its hardware-aware parallelism designs. To this end, this paper proposes the Coupled SSM model, for coupling state chains of multiple modalities while maintaining independence of intra-modality state processes. Specifically, in our coupled scheme, we devise an inter-modal hidden states transition scheme, in which the current state is dependent on the states of its own chain and that of the neighbouring chains at the previous time-step. To fully comply with the hardware-aware parallelism, we devise an expedite coupled state transition scheme and derive its corresponding global convolution kernel for parallelism. Extensive experiments on CMU-MOSEI, CH-SIMS, CH-SIMSV2 through multi-domain input verify the effectiveness of our model compared to current state-of-the-art methods, improved F1-Score by 0.4\%, 0.9\%, and 2.3\% on the three datasets respectively, 49\% faster inference and 83.7\% GPU memory save. The results demonstrate that Coupled Mamba model is capable of enhanced multi-modal fusion.

Motivated by the challenge of identifying intruder ions in a cold ion crystal, we investigate calorimetry from emitted fluorescence light. Under continuous Doppler cooling, the ion crystal reaches a temperature equilibrium with a fixed level of fluorescence intensity and any change in the motional energy of the crystal results in a modification of this intensity. We theoretically determine the fluorescence rate of an ion crystal as a function of the temperature, assuming that laser light is scattered along a two-level electronic transition, which couples to the crystal's vibrations via the mechanical effects of light. We analyze how the heat dissipated by collisions of an incoming intruder ion alters the scattering rate. We argue that an energy change by an incoming $^{229}$Th$^{10+}$ ion can be unambiguously detected within 100 $\mu$s via illuminating a fraction of a 10$^{3}$ ion crystal. This method enables applications including capture and spectroscopy of charged states of thorium isotopes and investigation of highly charged ions., Comment: 10 pages, 4 figures

A cesium atomic fountain clock is under development at Huazhong University of Science and Technology (HUST) in China. In this paper, we describe the construction of the entire fountain clock system and report the preliminary results. A frequency stability of $2.5\times 10^{-13} {\tau}^{-1/2}$ has been achieved by inter-comparison with a hydrogen maser, and the factors limiting the frequency stability are also discussed., Comment: 7 pages, 12 figures,26 references

We implement three-dimensional polarization gradient cooling of trapped ions. Counter-propagating laser beams near $393\,$nm impinge in lin$\,\perp\,$lin configuration, at a frequency below the S$_{1/2}$ to P$_{3/2}$ resonance in $^{40}$Ca$^+$. We demonstrate mean phonon numbers of $5.4(4)$ at a trap frequency of $2\pi \times 285\,$kHz and $3.3(4)$ at $2\pi\times480\,$kHz, in the axial and radial directions, respectively. Our measurements demonstrate that cooling with laser beams detuned to lower frequencies from the resonance is robust against an elevated phonon occupation number, and thus works well for an initial ion motion far out of the Lamb-Dicke regime, for up to four ions, and for a micromotion modulation index $\beta\leq 0.1$. Still, we find that the spectral impurity of the laser field influences both, cooling rates and cooling limits. Thus, a Fabry-P\'{e}rot cavity filter is employed for efficiently suppressing amplified spontaneous emission of the diode laser., Comment: 11 pages and 9 figures

Phase noise of the frequency synthesizer is one of the main limitations to the short-term stability of microwave atomic clocks. In this work, we demonstrated a low-noise, simple-architecture microwave frequency synthesizer for a coherent population trapping (CPT) clock. The synthesizer is mainly composed of a 100 MHz oven controlled crystal oscillator (OCXO), a microwave comb generator and a direct digital synthesizer (DDS). The absolute phase noises of 3.417 GHz signal are measured to be -55 dBc/Hz, -81 dBc/Hz, -111 dBc/Hz and -134 dBc/Hz, respectively, for 1 Hz, 10 Hz, 100 Hz and 1 kHz offset frequencies, which shows only 1 dB deterioration at the second harmonic of the modulation frequency of the atomic clock. The estimated frequency stability of intermodulation effect is 4.7*10^{-14} at 1s averaging time, which is about half order of magnitude lower than that of the state-of-the-art CPT Rb clock. Our work offers an alternative microwave synthesizer for high-performance CPT Rb atomic clock., Comment: 3 pages, 5 figures, 1 table

Ions of the isomer $^{229m}$Th are a topic of high interest for the construction of a "nuclear clock" and in the field of fundamental physics for testing symmetries of nature. They can be efficiently captured in Paul traps which are ideal for performing high precision quantum logic spectroscopy. Trapping and identification of long-lived $^{232}$Th$^{+}$ ions from a laser ablation source was already demonstrated by the TACTICa collaboration on Trapping And Cooling of Thorium Ions with Calcium. The $^{229m}$Th is most easily accessible as $\alpha$-decay daughter of the decay of $^{233}$U. We report on the development of a source for slow Th ions, including $^{229(m)}$Th for the TACTICa experiment. The $^{229(m)}$Th source is currently under construction and comprises a $^{233}$U monolayer, from which $^{229(m)}$Th ions recoil. These are decelerated in an electric field. Conservation of the full initial charge state distribution of the $^{229(m)}$Th recoil ions is one of the unique features of this source. We present ion-flight simulations for our adopted layout and give a final design. This source will provide Th ions in their original charge state at energies suitable for capture in a linear Paul trap for spectroscopy investigations., Comment: 6 pages, 3 figures, PLATAN19 conference proceeding published in Hyperfine Interact 2020

In this paper, we demonstrate a simple scheme of 6.835 GHz microwave frequency synthesizer based on the sub-sampling phase lock loop (PLL) technique. The application of the sub-sampling PLL is the key to simplify the architecture of the synthesizer in this scheme. A 100 MHz oven controlled crystal oscillator (OCXO) with ultra-low phase noise is used as the initial signal source. Then a dielectric resonant oscillator (DRO) of 6.8 GHz is directly phase locked to the 100 MHz OCXO utilizing the sub-sampling PLL. Benefiting from the sub-sampling PLL, the processes of microwave frequency multiplication and phase lock which are necessary in the development of microwave synthesizer are greatly simplified. Therefore, the architecture of the synthesizer is very simple. Correspondingly, the power consumption and cost of the synthesizer are low. The absolute phase noises of the 6.835 GHz output signal are measured to be -47 dBc/Hz, -77 dBc/Hz, -104 dBc/Hz and -121 dBc/Hz at 1 Hz, 10 Hz, 100 Hz and 1 kHz offset frequencies, respectively. he synthesizer can be used as the local oscillator of the Rb atomic clocks. For the Rb atomic clocks operated in the continuous or pulsed optically pumped (POP) mode, Tthe short-term frequency stability limited by the absolute phase noises of the synthesizer through the intermodulation or the Dick effect is theoretically calculated to be better than 5.0E10^-14/t^1/2. This low phase noise microwave frequency synthesizer can be used in other experiments of fundamental physics measurement.

We report on the development and phase noise performance of a 9.1926 GHz microwave frequency synthesizer to be used as the local oscillator for a Cs fountain clock. It is based on frequency multiplication and synthesis from an ultralow phase noise 5 MHz Oven Controlled Crystal Oscillator (OCXO) and 100 MHz Voltage Controlled Crystal Oscillator (VCXO).The key component of the frequency multiplication is a non-linear transmission-line (NLTL) used as a frequency comb generator. The phase noise of the synthesizer is improved by carefully optimizing the input power, the input and output impedances of the NLTL. The absolute phase noises of the 9.1926 GHz output signal are measured to be -64 dBc/Hz, -83 dBc/Hz, -92 dBc/Hz, -117 dBc/Hz and -119 dBc/Hz at 1 Hz, 10Hz, 100Hz, 1 kHz and 10 kHz offset frequencies, respectively. The residual phase noise of the synthesizer is measured to be -82 dBc/Hz at 1 Hz offset frequency. The measurement result shows that the absolute phase noise at the frequency range of 1 - 100 Hz is mainly limited by the phase noise of the OCXO. The contribution of the absolute phase noise to the fountain clock short-term frequency stability is calculated to be 7.0x10^(-14). The residual frequency stability of the synthesizer is measured to be1.5x10^(-14), which is consistent with the calculated frequency stability due to the residual phase noise of the synthesizer. Meanwhile we designed and realized an interferometric microwave switch in the synthesizer to eliminate the frequency shifts induced by the microwave leakage. The extinction ratio of the switch is measured to be more than 50 dB. In the scheme, we use only commercially available components to build the microwave frequency synthesizer with excellent phase noise performance for high-performance Cs fountain clocks.