Progress in atomic, optical and quantum science has led to rapid improvements in atomic clocks. At the same time, atomic clock research has helped to advance the frontiers of science, affecting both fundamental and applied research. The ability to control quantum states of individual atoms and photons is central to quantum information science and precision measurement, and optical clocks based on single ions have achieved the lowest systematic uncertainty of any frequency standard. Although many-atom lattice clocks have shown advantages in measurement precision over trapped-ion clocks, their accuracy has remained 16 times worse. Here we demonstrate a many-atom system that achieves an accuracy of 6.4 × 10(-18), which is not only better than a single-ion-based clock, but also reduces the required measurement time by two orders of magnitude. By systematically evaluating all known sources of uncertainty, including in situ monitoring of the blackbody radiation environment, we improve the accuracy of optical lattice clocks by a factor of 22. This single clock has simultaneously achieved the best known performance in the key characteristics necessary for consideration as a primary standard-stability and accuracy. More stable and accurate atomic clocks will benefit a wide range of fields, such as the realization and distribution of SI units, the search for time variation of fundamental constants, clock-based geodesy and other precision tests of the fundamental laws of nature. This work also connects to the development of quantum sensors and many-body quantum state engineering (such as spin squeezing) to advance measurement precision beyond the standard quantum limit.

The pursuit of better atomic clocks has advanced many research areas, providing better quantum state control, new insights in quantum science, tighter limits on fundamental constant variation and improved tests of relativity. The record for the best stability and accuracy is currently held by optical lattice clocks. Here we take an important step towards realizing the full potential of a many-particle clock with a state-of-the-art stable laser. Our 87Sr optical lattice clock now achieves fractional stability of 2.2 × 10−16 at 1 s. With this improved stability, we perform a new accuracy evaluation of our clock, reducing many systematic uncertainties that limited our previous measurements, such as those in the lattice ac Stark shift, the atoms' thermal environment and the atomic response to room-temperature blackbody radiation. Our combined measurements have reduced the total uncertainty of the JILA Sr clock to 2.1 × 10−18 in fractional frequency units.

Cooling atoms to ultralow temperatures have produced a wealth of opportunities in fundamental physics, precision metrology, and quantum science. The more recent application of sophisticated cooling techniques to molecules, which have been more challenging to develop due to complex molecular structures, has now opened door to the longstanding goal of precisely controlling molecular internal and external degrees of freedom and the resulting interaction processes. This line of research can leverage fundamental insights into how molecules interact and evolve to enable the control of reaction chemistry and the design and realization of a range of advanced quantum materials. 2 Molecules hold a central place in the physical sciences. On the one hand, molecules consisting of a small number of atoms represent the upper limit of complexity we can at present hope to understand in complete detail, starting from quantum mechanics. On the other hand, molecules are the building blocks from which more complex phenomena emerge, including chemistry, condensed matter, and indeed life itself. These molecules then represent a kind of intellectual fulcrum around which we can leverage our complete understanding of small systems to probe and manipulate increasingly complex ones.Precisely controlled studies of molecules started decades ago, with the invention of supersonic molecular beams for cooling (1) and coherent control for manipulation of internal states (2). However, bringing the temperature of molecular gases to the quantum regime is a relatively recent endeavor (3). When molecules move extremely slowly in the laboratory frame, and control of their internal degrees of freedom is achieved at the individual quantum state level, then each step of a complex chemical reaction can in principle be monitored and measured. The energy resolution underpinning such a process would be limited only by fundamental quantum rules that govern the molecular interaction from start to finish. The capability to track in full detail how multiple molecular species approach each other, interact via their evolving potential energy landscape, form intermediates, and re-emerge as final products, all while monitoring the internal and external energy level distributions, may have seemed out of reach only a few years ago.However, thanks to the recent progress in the field of cold molecules, we could soon be able to do precisely that. First-principle understanding of the most fundamental molecular reaction processes will furthermore enable the design and control of complex molecular transformations and materials with powerful functionality. 3Molecules have rich energy level structures, owing to the vibrational and rotational degrees of freedom, compared to atoms. This presents a challenge for cooling technology. However, once we gain control over these molecular degrees of freedom, we create opportunities to take advantage of their unique properties, such as precise manipulation of long-range interactions mediated by molecular electric dipole moments. ...

Strontium optical lattice clocks have the potential to simultaneously interrogate millions of atoms with a high spectroscopic quality factor of 4 × 10 Previously, atomic interactions have forced a compromise between clock stability, which benefits from a large number of atoms, and accuracy, which suffers from density-dependent frequency shifts. Here we demonstrate a scalable solution that takes advantage of the high, correlated density of a degenerate Fermi gas in a three-dimensional (3D) optical lattice to guard against on-site interaction shifts. We show that contact interactions are resolved so that their contribution to clock shifts is orders of magnitude lower than in previous experiments. A synchronous clock comparison between two regions of the 3D lattice yields a measurement precision of 5 × 10 in 1 hour of averaging time.

It has long been expected that quantum degenerate gases of molecules would open access to a wide range of phenomena in molecular and quantum sciences. However, the very complexity that makes ultracold molecules so enticing has made reaching degeneracy an outstanding experimental challenge over the past decade. We now report the production of a Fermi degenerate gas of ultracold polar molecules of potassium-rubidium (KRb). Through coherent adiabatic association in a deeply degenerate mixture of a rubidium Bose-Einstein condensate and a potassium Fermi gas, we produce molecules at temperatures below 0.3 times the Fermi temperature. We explore the properties of this reactive gas and demonstrate how degeneracy suppresses chemical reactions, making a long-lived degenerate gas of polar molecules a reality.Ultracold polar molecules have received attention as ideal candidates to realize a plethora of proposals in molecular and many-body physics. These include the development of chemistry in the quantum regime [1], the emulation of strongly interacting lattice spin models [2-6], the production of topological phases in optical lattices [7-10], the exploration of fundamental symmetries [11][12][13][14][15], and the study of quantum information science [16][17][18]. While magnetic atoms also exhibit long-ranged dipolar interactions and can be used to carry out these proposals [19,20], polar molecules offer more tunable, stronger interactions and additional degrees of freedom. A low-entropy, quantum degenerate sample is a prerequisite for many of these explorations.The intrinsic complexity of molecules relative to atoms, owing to the additional rotational and vibrational degrees of freedom, has made their cooling to ultralow temperatures one of the most significant experimental challenges in molecular physics [21]. While the direct laser cooling of certain diatomic molecules has progressed enormously in recent times so that magneto-optic [22][23][24][25] and pure optical [26] trapping have been demonstrated, phase space density in these systems remains many orders of magnitude away from degeneracy. To date, by far the coldest diatomic molecules have been made by cooling atoms to a few hundred nanokelvin (10 −9 K) and coherently associating the ultracold atoms into deeply bound molecules using a Fano-Feshbach resonance [27] fol-lowed by stimulated Raman adiabatic passage (STI-RAP) [28].

Many-particle optical lattice clocks have the potential for unprecedented measurement precision and stability due to their low quantum projection noise. However, this potential has so far never been realized because clock stability has been limited by frequency noise of optical local oscillators. By synchronously probing two ^{87}Sr lattice systems using a laser with a thermal noise floor of 1×10(-15), we remove classically correlated laser noise from the intercomparison, but this does not demonstrate independent clock performance. With an improved optical oscillator that has a 1×10(-16) thermal noise floor, we demonstrate an order of magnitude improvement over the best reported stability of any independent clock, achieving a fractional instability of 1×10(-17) in 1000 s of averaging time for synchronous or asynchronous comparisons. This result is within a factor of 2 of the combined quantum projection noise limit for a 160 ms probe time with ~10(3) atoms in each clock. We further demonstrate that even at this high precision, the overall systematic uncertainty of our clock is not limited by atomic interactions. For the second Sr clock, which has a cavity-enhanced lattice, the atomic-density-dependent frequency shift is evaluated to be -3.11×10(-17) with an uncertainty of 8.2×10(-19).

Using a narrow intercombination line in alkaline earth atoms to mitigate large inelastic losses, we explore the Optical Feshbach Resonance (OFR) effect in an ultracold gas of bosonic 88 Sr. A systematic measurement of three resonances allows precise determinations of the OFR strength and scaling law, in agreement with coupled-channels theory. Resonant enhancement of the complex scattering length leads to thermalization mediated by elastic and inelastic collisions in an otherwise ideal gas. OFR could be used to control atomic interactions with high spatial and temporal resolution.PACS numbers: 34.50. Rk, 34.50.Cx, 32.80.Qk The ability to control the strength of atomic interactions has led to explosive progress in the field of quantum gases for studies of few-and many-body quantum systems. This capability is brought about by magnetic field-induced Feshbach scattering resonances (MFR) [1], where both the magnitude and sign of low-energy atomic interactions can be varied by coupling free particles to a molecular state. MFR in ultracold alkali atoms have been used to realize novel few-body quantum states and study strongly correlated many-body systems and phase transitions [1, 2]. However, magnetic tuning has limited current experiments to relatively slow time scales and low spatial resolution. Higher resolution could be achieved by controlling MFR optically [3].Scattering resonances can also arise under the influence of laser light tuned near a photoassociation (PA) resonance [4] where free atom pairs are coupled to an excited molecular state [5, 6]. This Optical Feshbach Resonance (OFR) is expected to enable new and powerful control with high spatial and temporal resolution. OFR has been studied in thermal [7] and degenerate [8, 9] gases of Rb, but it was not found useful due to large photoassociative losses. Much narrower optical intercombination lines are available in alkaline earth atoms and are predicted to overcome this loss problem [10]. Independently, ultracold alkaline earth atoms have recently emerged to play leading roles for quantum metrology [11][12][13] where precision measurement and many-body quantum systems are combined to study new quantum phenomena [14, 15]. Degenerate gases of alkaline earth atoms have recently become available [16]. Due to the lack of magnetic structure in the ground state of these atoms, the OFR effect could become an important tool for controlling their interactions. OFR work on Yb [17, 18] has been limited to studying the induced change in scattering phase shifts and PA rates. Dominant PA losses are evident in all of the OFR experiments listed above. Light-induced elastic collisions for thermalization were not observed.In this Letter, we study the OFR effect across multiple resonances in a metastable molecular potential of 88 Sr. The aim of this work is to test the practical applicability of OFR for engineering atomic interactions in the presence of loss, similar to the successful application of a decaying MFR [19]. For 88 Sr, OFR is predicted [10] to allow changes in ...

The preparation of large, low-entropy, highly coherent ensembles of identical quantum systems is foundational for many studies in quantum metrology [1], simulation [2], and information [3]. Here, we realize these features by leveraging the favorable properties of tweezer-trapped alkaline-earth atoms [4][5][6] while introducing a new, hybrid approach to tailoring optical potentials that balances scalability, high-fidelity state preparation, site-resolved readout, and preservation of atomic coherence. With this approach, we achieve trapping and optical clock excited-state lifetimes exceeding 40 seconds in ensembles of approximately 150 atoms. This leads to half-minute-scale atomic coherence on an optical clock transition, corresponding to quality factors well in excess of 10 16 . These coherence times and atom numbers reduce the effect of quantum projection noise to a level that is on par with leading atomic systems [7,8], yielding a relative fractional frequency stability of 5.2(3) × 10 −17 (τ /s) −1/2 for synchronous clock comparisons between sub-ensembles within the tweezer array. When further combined with the microscopic control and readout available in this system, these results pave the way towards long-lived engineered entanglement on an optical clock transition [9] in tailored atom arrays.