Clocks that are based on atomic and molecular transitions can serve as unparalleled sensors of fundamental phenomena. In particular, a clock based on vibrations in a diatomic molecule is a highly precise sensor of the interatomic force, including possible contributions from new physics. Such a clock is also of metrological interest, since vibrational states in homonuclear molecules have extremely long lifetimes. We present the technique of near-resonant magic-wavelength trapping for strontium dimers, which allows us to reach coherence times exceeding 100 ms for far-separated vibrational state superpositions. The development of the molecular clock is accelerated through state-of-the-art quantum chemistry work.
Clocks that are based on atomic and molecular transitions can serve as unparalleled sensors of fundamental phenomena. In particular, a clock based on vibrations in a diatomic molecule is a highly precise sensor of the interatomic force, including possible contributions from new physics. Such a clock is also of metrological interest, since vibrational states in homonuclear molecules have extremely long lifetimes. We present the technique of near-resonant magic-wavelength trapping for strontium dimers, which allows us to reach coherence times exceeding 100 ms for far-separated vibrational state superpositions. The development of the molecular clock is accelerated through state-of-the-art quantum chemistry work.
Over the past few decades, rapid development of laser cooling techniques and narrow-linewidth lasers have allowed atom-based quantum clocks to achieve unprecedented precision. Techniques originally developed for atomic clocks can be extended to ultracold molecules, with applications ranging from quantum-state-controlled ultracold chemistry to searches for new physics. Because of the richness of molecular structure, quantum metrology based on molecules provides possibilities for testing physics that is beyond the scope of traditional atomic clocks. This thesis presents the work performed to establish a state-of-the-art quantum clock based on ultracold molecules. The molecular clock is based on a frequency difference between two vibrational levels in the electronic ground state of 88Sr2 diatomic molecules. Such a clock allows us test molecular QED, improve constraints on nanometer-scale gravity, and potentially provide a model-independent test of temporal variations of the proton-electron mass ratio. Trap-insensitive spectroscopy is crucial for extending coherent molecule-light interactions and achieving a high quality factor Q. We have demonstrated a magic wavelength technique for molecules by manipulating the optical lattice frequency near narrow polarizability resonances. This general technique allows us to increase the coherence time to tens of ms, an improvement of a factor of several thousand, and to narrow the linewidth of a 25 THz vibrational transition initially to 30 Hz. This width corresponds to the quality factor Q=8x10^11. Besides the molecular quantum metrology, investigations of novel phenomena in state-selected photodissociation are also described in this thesis, including magnetic-field control of photodissociation and observation of the crossover from ultracold to quasiclassical chemistry.
Ultracold molecules are a powerful platform for metrology, precision measurements and searches for new, beyond-the-Standard-Model physics. Sr2, thanks to its simple structure, insensitivity to external fields and narrow optical transitions, provides an excellent testbed for the search for new interactions. Here, we present a detailed characterization of our 88Sr2 molecular clock for a vibrational transition spanning the entire depth of the ground state potential. We also discuss prospects to use strontium isotopologues to place improved constraints on new mass-dependent forces, including possible pathways toward the production of ultracold 86Sr2 and 84Sr2 dimers and spectroscopy of clock lines in these species for use in the search for new mass-dependent forces.
Abstract : We have established the strontium molecular clock as the leading ultracold-molecule precision measurement platform. We can fully control the molecules internal and external quantum states, as in state-of-the-art atomic lattice clocks. Using the quantized molecular spectra in an optical lattice, we devised a new lattice thermometry method that is advantageous for many lattice experiments, including clocks and manybody physics studies. The full quantum control allowed us to observe deeply subradiant molecular states, and coherently control them. We measured lifetimes enhanced by up to 300 times. Ultranarrow transitions to these states permitted a rigorous study of asymptotic physics at the atom-molecule threshold. We proved that subradiant states can decay to the ground state via higher-order electromagnetic transitions, with a rate that grows as the square of the bond length, and are quenched by predissociation at a rate proportional to the vibrational level spacing. We introduced a precise technique for measuring molecular binding energies via photofragmentation; controlled forbidden optical transition strengths with weak magnetic fields by five orders of magnitude; and explained anomalously large magnetic susceptibilities of the asymptotic molecules. The unprecedented precision, coupled with advanced ab initio theory, paves the way to exciting new directions for the molecular clock.
in a lattice. Sr2 has a range of electronically excited bound states which are readily accessible with optical wavelengths using the narrow 1S0->3P1 intercombination line. As in Nat. Phys. 11, 32, we measure the lifetimes of the narrow, deeply-bound subradiant states in the 1g (1S0+3P1 dissociative limit) potential, allowing for coherent control of molecules and a comparison with theoretical predictions of the lifetimes and transition strengths of these states. Next, we study ultracold photodissociation of Sr2 molecules through abortion of one and two photons near the atomic intercombination line. This allows us to observe the vector character of transition elements through the angular dissociation pattern and to directly measure barrier heights in the excited state potentials. Finally, as shown in PRL 114, 023001, we demonstrate that in a non-magic lattice, a narrow transition can be used to measure the trapped gas temperature through the linewidth of the spectral feature corresponding to the carrier transitions. We use this technique to measure the temperature of Sr2 molecules to 10x higher precision than with standard techniques. We discuss future prospects with this molecular lattice clock. 1 Funding from NIST, ARO, and NSF IGERT
Neutral quantum absorbers in optical lattices have emerged as a leading platform for achieving clocks with exquisite spectroscopic resolution.However, the studies of these clocks and their systematic shifts have so far been limited to atoms.Here, we extend this architecture to an ensemble of diatomic molecules and experimentally realize an accurate lattice clock based on pure molecular vibration.We evaluate the leading systematics, including the characterization of nonlinear trap-induced light shifts, achieving a total systematic uncertainty of 4.6 × 10 -14 .The absolute frequency of the vibrational splitting is measured to be 31 825 183 207 592.8(5.1)Hz, enabling the dissociation energy of our molecule to be determined with record accuracy.Our results represent an important milestone in molecular spectroscopy and THzfrequency standards, and may be generalized to other neutral molecular species with applications for fundamental physics, including tests of molecular quantum electrodynamics and the search for new interactions.
This paper explores the potential of quantum sensors for achieving unprecedented levels of precision in time measurement. The core concept leverages the inherent sensitivity of quantum systems to external perturbations, particularly quantum entanglement and coherence, to directly measure the passage of time. Traditional timekeeping methods rely on periodic phenomena like atomic oscillations, which introduce systematic errors and limitations. Quantum sensors, however, offer a fundamentally different approach, promising a shift towards a measurement paradigm where time itself is directly sensed. This work details a theoretical framework for such a system, outlining key components, potential challenges, and the anticipated improvements in accuracy compared to existing technologies. We propose a system utilizing a macroscopic quantum clock, exploiting the precisely controlled evolution of quantum superposition states to determine time intervals with potentially sub-picosecond resolution. The design emphasizes the minimization of decoherence effects—a critical factor in realizing the full potential of quantum time measurement—and introduces novel strategies for signal processing and calibration. This research contributes to the emerging field of quantum metrology and lays the groundwork for future advancements in high-precision timekeeping and fundamental physics research. ---