Invited Speakers

This work presents a method for the wafer-scale integration of epitaxial α-quartz thin films on standard silicon through a soft-chemistry approach. This technique enables the scalable, and sustainable manufacturing of piezoelectric MEMS (Micro-Electro-Mechanical Systems) and NEMS (Nano-Electro-Mechanical Systems) resonators suitable for sensing applications. The process produces epitaxial α-quartz (100) films across wafer-sized areas, featuring device-quality microstructures that are compatible with CMOS (Complementary Metal-Oxide-Semiconductor). This opens up possibilities for integrating bioNEMS and RF (Radio Frequency) components. Resonators made from these α-quartz layers exhibit high quality factors in both air and liquid environments. The film-level piezoelectric response aligns with the symmetry of α-quartz, allowing for operation in the super high-frequency range i.e., 17.8 GHz with a quality factor of 280 which represents a QxF product of 4.98·exp12 when scaled down to NEMS geometries. BioNEMS demonstrations for virus detection showcase both high sensitivity and the potential for integration on 4-inch wafers, indicating a viable path toward diagnostic applications. 

 In this work, we have demonstrated single crystalline ScAlN epilayers on buffered AlN on Si (111) grown by MBE. The films are atomically smooth and free from cracks and exhibit excellent crystalline quality along the out-of-plane (0002) direction. Piezoelectric force microscopy results showed an increase in d33 with increasing Sc composition, with a maximum of 25.7 pC/N for Sc content ~ 30%. This is primarily driven by the expansion in the lattice parameter a, as observed from statistical analysis of 4D-STEM images. Utilizing the enhanced in-plane crystallinity of MBE grown ScAlN-on-Si films, we have further demonstrated extensional mode BAW resonators with an ultra-high Q of approximately 97k at 70.276 MHz, resulting in a frequency-Q product of ~ 6.86 × 10¹². The attainment of in-plane single crystalline ScAlN films on Si by MBE and high-performance device results reported in this work show a clear path to achieve enhanced piezoelectric transduction for next generation acoustic devices. 

 We report the development of microelectromechanical (MEMS) frequency references designed for holdover applications, in which parts-per-trillion level fractional frequency stability is required over extended periods. The foundation of our references are wafer-level encapsulated silicon resonators that support multiple vibrational modes.

We discuss the technique for high-resolution measurements of thermal fluctuations exhibited by microwave and mechanical resonators. Thus, for the room-temperature-stabilized 9 GHz sapphire-loaded cavity resonator, we observed more than 16 dB improvement in the thermal noise peak contrast when using the dual-channel measurement system, as compared to the single-channel counterpart. The proposed technique may benefit the laboratory search for dark matter that relies on cryogenic microwave resonators. 

The introduction of digital signal processing (DSP) assisted coherent detection has been a cornerstone of modern fiber-optic communication systems. The ability to digitally, i.e. after analogue-to-digital converter, compensate for chromatic dispersion, polarization mode dispersion, and phase noise has rendered traditional analog feedback loops largely obsolete. While analog techniques remain prevalent for phase noise characterization of single-frequency lasers, the phase noise characterization of optical frequency combs presents a greater challenge. This complexity arises from different number of phase noise sources affecting an optical frequency comb. Here, we show how a phase noise measurement techniques method based on multi-heterodyne coherent detection and DSP-based subspace tracking can be used to identify, measure and quantify various phase noise sources associated with an optical frequency comb. 

The evolution of MHz oscillators has focused on miniaturization, higher precision, lower power consumption, and improved reliability. AT-cut quartz oscillators in SMD ceramic packages now achieve compact dimensions down to 2.0 × 1.2 × 0.75 mm³, thanks to advanced thermosonic flip-chip bonding, which supports high-temperature operation (up to 210 °C) and reduces aging. These devices feature start-up times under 5 ms and operating currents below 5 mA, making them ideal for precision-critical applications such as drilling heads and medical implants. Moreover, OCXOs (Oven Controlled Crystal Oscillators) provide frequency stability better than ±250 ppb over a –40 to 85 °C temperature range. 

The performance of microwave atomic clocks is intricately linked to the characteristics of the laser systems employed for quantum state preparation and detection. Here, we present recent breakthroughs in enhancing three distinct microwave atomic clocks-the CPT chip-scale atomic clock, the optically pumped compact cesium beam clock, and the rubidium fountain clock-through the strategic integration of three specialized lasers: the high-speed directly modulated external cavity semiconductor laser, the Faraday laser and the one-click auto-locking laser. 

 The ability of producing ultracold atoms in microgravity allows to probe the nature of gravitation, and push the boundaries of quantum physics reaching the regime of ultra-low temperature and novel topologies. Our team develops all optical techniques to produce ultra cold atoms and perform atom interferometry in weightlessness. Our microgravity platforms are versatile facilities to prepare future Space missions for fundamental physics and geosciences. 

Optical frequency combs with line spacing between 15-30 GHz can be used for calibration of spectrographs mounted on large telescopes and have gained considerable interest due to the high line frequency stability and uniform spacing. We report our progress towards developing a portable, remotely operated optical frequency comb in the 500-900 nm band aimed for calibration of the astronomical spectrographs, particularly the G-CLEF spectrograph of the GMT telescope. We describe two approaches based on electro-optical modulation of an acetylene- stabilized laser at 1542 nm, combined with nonlinear spectral broadening and frequency conversion. The first uses a resonant modulator while the second uses two intensity modulators, both driven by low a noise source at 20 GHz. 

This work reports a passive wireless temperature sensor based on a piezoelectric substrate integrating both an antenna and an acoustic MEMS resonator for harsh-environment monitoring. A leaky surface acoustic wave (LSAW) resonator combined with a split-arc on-chip electrically small antenna enables wireless temperature sensing up to 550 °C with extremely good linearity. The system is monolithically fabricated on the same substrate with a single lithographic step, providing a compact and passive solution for temperature sensing in harsh environments. 

 Multicore optical fibers (MCFs) offer a unique platform for both long-haul frequency transfer and quantum network synchronization. We review our work in frequency transfer over MCF, with fractional frequency transfer stability of 3x10-19 at 10,000 s averaging over a 25 km long deployed fiber, as well as fiber noise cancellation over 40 km with sub-femtosecond core-to-core timing jitter and low crosstalk for quantum networking applications. 

The international metrology community is preparing for a redefinition of the SI second based on optical clocks. To assess the consistency of these systems, we conducted a series of international comparison campaigns from 2022 to 2025 using the European optical fiber network, satellite frequency transfer, and transportable clocks. Optical frequency standards in six countries, spanning ion and lattice systems based on In⁺, Hg, Yb⁺(E2), Yb⁺(E3), Yb, Sr⁺, and Sr were compared, yielding over 50 frequency ratios with uncertainties from 4×10⁻¹⁸ to 3×10⁻¹⁶. The results enabled cross-validation across a large network of independent clocks, identifying some technical issues and some inconsistencies up to 1×10⁻¹⁶, while confirming the robustness of most measurements. These results motivate continued investigations, improvements of the network, and further discussions within the community about the timeline and options for the redefinition. 

This talk will present some of the conclusions of the work done within the CCTF Task Group on Moon Timing, (i) to clarify the possible options for a reference time on the Moon and its realization based on our timekeeping experience on Earth, (ii) to understand possible operational constraints of the space agencies associated with the different options, and (iii) to ensure a frame which ensures the traceability of future realizations of Lunar Time to UTC. We will also present the recommendation draft that the CCTF intends to submit to the Conférence Générale des Poids et Mesures in 2026. 

The ACES mission tests General Relativity and enables high-precision global time and frequency transfer using the PHARAO cold atom clock onboard the ISS and a worldwide network of ground clocks. Its Microwave Link (MWL) is a coherent, bi-directional, three-frequency system that cancels first-order propagation delays and combines code-phase and carrier-phase measurements to achieve high stability. Dedicated analysis pipelines correct for atmospheric, geometric, and instrumental effects, validated through in-orbit measurements and test loop translators. Initial in-orbit commissioning involved four ground terminals in Europe and the US, enabling common-view and non-common-view comparisons. Independent analyses at ESTEC and LTE show consistent results, with space-to-ground time transfer stability approaching a few parts in 10¹⁴ at 100 s over a single ISS pass and phase continuity at the tens of picoseconds level. Ongoing work refines calibrations and extends validation against fiber and TWSTFT links, marking the first full in-flight verification of the MWL and a key milestone toward testing the gravitational redshift at the ppm level. 

 Programmable neutral-atom arrays have emerged as a leading platform for quantum science experiments, ranging from quantum computing and simulation to metrology. In particular, arrays of alkaline-earth atoms offer optical-clock qubits with long coherence times, scalability to large qubit numbers, and tunable Rydberg-mediated interactions. These features provide an ideal setting for exploring how microscopic control and entanglement can improve the performance of optical atomic clocks beyond conventional limits. This talk will cover two efforts in this area. First, I will present recent results from JILA demonstrating entanglement-enhanced optical-clock operation. Second, I will briefly introduce our new experiment under development at Caltech. Together, these efforts highlight the potential for programmable atom arrays to enable new capabilities at the intersection of precision measurement and quantum information processing. 

 We investigate the temperature-dependency of birefringent effects in crystalline AlGaAs/GaAs and nitrogen-dilute AlGaAsN/GaAs mirror coatings. Using a dual-frequency modulation technique in a low-vibration cryostat, we measure the frequency splitting of polarization eigenmodes from room temperature to 5 K. Our results show that the birefringent line splitting increases by about 5% upon cooling, and its response to step changes in intracavity power varies strongly in both amplitude and transient duration. These findings provide new insights into the temperature dependency of birefringence effects in crystalline coatings. A better understanding of these effects is essential for developing mitigation strategies for the associated noise sources or improved coating designs for the next generation of ultra-stable optical cavities.

 We report on a new 27Al+ clock with fractional systematic uncertainty of 5.5e-19 and with long term instability of 3.5e-16 /√τ, the latter is the lowest of any ion-based clock. We also report on frequency ratio measurement against Sr and Yb lattice clocks with total fractional uncertainty in the ratios of 2.2e-18 and 3.2e-18, respectively. Lastly, we'll discuss the work being done to upgrade the system to work with multiple 27Al ions, further improving on the time to average out statistical uncertainty by a factor of 4. 

Optical frequency references based on the two-photon transition in rubidium at 778 nm are a promising platform high-performance, compact optical timing applications. In typical operation, their overall frequency stability faces a tradeoff between improving the short-term performance at the expense of increasing the long-term instability due to the AC Stark shift. Here we experimentally demonstrate a method that provides active compensation of the AC Stark shift, enabling operation of the optical frequency reference with a fractional frequency instability at or below 3 x 10-14 for time scales from 1 s to 105 s.