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.

We investigate the stability of a three spin state mixture of ultracold fermionic 6 Li atoms over a range of magnetic fields encompassing three Feshbach resonances. For most field values, we attribute decay of the atomic population to three-body processes involving one atom from each spin state and find that the three-body loss coefficient varies by over four orders of magnitude. We observe high stability when at least two of the three scattering lengths are small, rapid loss near the Feshbach resonances, and two unexpected resonant loss features. At our highest fields, where all pairwise scattering lengths are approaching at = −2140a0, we measure a three-body loss coefficient L3 ≃ 5 × 10 −22 cm 6 /s and a trend toward lower decay rates for higher fields indicating that future studies of color superfluidity and trion formation in a SU(3) symmetric Fermi gas may be feasible.

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We observe enhanced three-body recombination in a three-component ;{6}Li Fermi gas attributable to an excited Efimov trimer state intersecting the three-atom scattering threshold near 895 G. From measurements of the recombination rate we determine the Efimov parameters kappa_{*} and eta_{*} for the universal region above 600 G which includes three overlapping Feshbach resonances. The value of kappa_{*} also predicts the locations of loss features previously observed near 130 and 500 G [T. B. Ottenstein, Phys. Rev. Lett. 101, 203202 (2008)10.1103/PhysRevLett.101.203202; J. H. Huckans, Phys. Rev. Lett. 102, 165302 (2009)10.1103/PhysRevLett.102.165302] suggesting they are associated with a ground-state Efimov trimer near threshold. We also report on the realization of a degenerate three-component Fermi gas with approximate SU(3) symmetry.

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 ...

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We describe the Quantum Test of the Equivalence principle and Space Time (QTEST), a concept for an atom interferometry mission on the International Space Station (ISS). The primary science objective of the mission is a test of Einstein's equivalence principle with two rubidium isotope gases at a precision of better than 10 −15 , a 100-fold improvement over the current limit on equivalence principle violations, and over 1,000,000 fold improvement over similar quantum experiments demonstrated in laboratories. Distinct from the classical tests is the use of quantum wave packets and their expected large spatial separation in the QTEST experiment. This dual species atom interferometer experiment will also be sensitive to time-dependent equivalence principle violations that would be signatures for ultralight dark-matter particles. In addition, QTEST will be able to perform photon recoil measurements to better than 10 −11 precision. This improves upon terrestrial experiments by a factor of 100, enabling an accurate test of the standard model of particle physics and contributing to mass measurement, in the proposed new international system of units (SI), with significantly improved precision. The predicted high measurement precision of QTEST comes from the microgravity environment on ISS, offering extended free fall times in a well-controlled environment. QTEST plans to use high-flux, dual-species atom sources, and advanced cooling schemes, for N>10 6 non-condensed atoms of each species at temperatures below 1 nK. Suppression of systematic errors by use of symmetric interferometer configurations and rejection of commonmode errors drives the QTEST design. It uses Bragg interferometry with a single laser beam at the 'magic' wavelength, where the two isotopes have the same polarizability, for mitigating sensitivities to vibrations and laser noise, imaging detection for correcting cloud initial conditions and maintaining contrast, modulation of the atomic hyperfine states for reduced sensitivity to magnetic field gradients, two source-regions for simultaneous time reversal measurements and redundancy, and modulation of the gravity vector using a rotating platform to reduce otherwise difficult systematics to below 10 −16 . dilatons or moduli [6]. Such tests may thus be one of the best chances to detect new physics beyond the standard model.Recent advances in ultra-cold atom physics and atom interferometry have provided new measurement capabilities [7][8][9][10][11][12][13][14], with which the EP can be tested to unprecedented precisions. Already, laboratory experimental investigations have been carried out with atomic matter waves for tests of the equivalence principle [14][15][16][17][18][19], for precise photon recoil measurements [20,21], and for tests of inverse square laws of gravity [22][23][24]. The Quantum Test of the Equivalence principle and Space Time (QTEST) will fundamentally be a set of lightpulse atom interferometer (AI) experiments. Its primary science objective is to measure the differential gravitational a...