We report the results of a new experimental search for a permanent electric dipole moment of 199 Hg utilizing a stack of four vapor cells. We find d( 199 Hg) = (0.49±1.29stat ±0.76syst)×10 −29 e cm, and interpret this as a new upper bound, |d( 199 Hg)| < 3.1×10 −29 e cm (95% C.L.). This result improves our previous 199 Hg limit by a factor of 7, and can be used to set new constraints on CP violation in physics beyond the standard model. PACS numbers: 11.30.Er,32.10.Dk,32.80.Xx,24.80.+y The existence of a finite permanent electric dipole moment (EDM) of a particle or atom would violate time reversal symmetry (T ), and would also imply violation of the combined charge conjugation and parity symmetry (CP ) through the CP T theorem [1,2,3]. EDMs are suppressed in the standard model of particle physics (SM), lying many orders of magnitude below current experimental sensitivity. However, it is thought that additional sources of CP violation are needed to account for baryogenesis [4,5], and many theories beyond the SM, such as supersymmetry [6,7], naturally predict EDMs within experimental reach.Experimental searches for EDMs have so far yielded null results. The most precise and significant limits have been set on the EDM of the neutron [8], the electron [9], and the 199 Hg atom [10], leading to tight constraints on supersymmetric extensions of the SM [7]. Here we report the first result of a new mercury experiment, |d( 199 Hg)| < 3.1×10−29 e cm (95% C.L.), which improves our previous limit [10] by a factor of 7 and provides a yet more exacting probe of possible new sources of CP violation.199 Hg has a 1 S 0 electronic ground state and nuclear spin 1/2. An EDM of the ground state atom would point along the nuclear spin axis and arise mainly from CP violation in the nucleus. We measure the nuclear Larmor frequency ν given by hν = |2µB ± 2dE|, where µ and d are the 199 Hg magnetic and electric dipole moments, and B and E are the magnitudes of external magnetic and electric fields aligned parallel (+) or antiparallel (−) with each other. The signature for d = 0 is thus a shift in Larmor frequency when E is reversed relative to B.As shown in Fig. 1, our new apparatus uses a stack of four spin-polarized Hg vapor cells in a common B-field. The middle two cells have oppositely directed E-fields, resulting in EDM-sensitive Larmor shifts of opposite sign; the outer two cells, enclosed by the high voltage (HV) electrodes and thus placed at E = 0, are free of EDM effects and serve to cancel B-field gradient noise and provide checks for spurious HV-correlated B-field shifts.The vapor cells are constructed from high purity fused silica and contain isotopically enriched 199 Hg (92 %) at a density of 4 × 10 13 cm −3 , a paraffin wall coating, and 475 Torr of CO buffer gas. CO efficiently quenches excited state 199 Hg and thus reduces degradation of the wall coating [11]. Spin coherence times T 2 are 100 to 200 sec. A conductive SnO coating on the cell end-caps provides electric field plates separated by 11 mm. The average leakage...

Strongly interacting quantum many-body systems are fundamentally compelling and ubiquitous in science. However, their complexity generally prevents exact solutions of their dynamics. Precisely engineered ultracold atomic gases are emerging as a powerful tool to unravel these challenging physical problems. Here we present a new laboratory for the study of many-body effects: strongly interacting two-level systems formed by the clock states in 87 Sr, which are used to realize a neutral atom optical clock that performs at the highest level of optical-atomic coherence and with precision near the limit set by quantum fluctuations. Our measurements of the collective spin evolution reveal signatures of many-body dynamics, including beyond-mean-field effects. We derive a many-body Hamiltonian that describes the experimental observation of severely distorted lineshapes, atomic spin coherence decay, density-dependent frequency shifts, and correlated quantum spin noise. These investigations open the door to exploring quantum many-body effects and entanglement in quantum systems with optical energy splittings, using highly coherent and precisely controlled optical lattice clocks.

Optical lattice clocks with extremely stable frequency are possible when many atoms are interrogated simultaneously, but this precision may come at the cost of systematic inaccuracy resulting from atomic interactions. Density-dependent frequency shifts can occur even in a clock that uses fermionic atoms if they are subject to inhomogeneous optical excitation. However, sufficiently strong interactions can suppress collisional shifts in lattice sites containing more than one atom. We demonstrated the effectiveness of this approach with a strontium lattice clock by reducing both the collisional frequency shift and its uncertainty to the level of 10(-17). This result eliminates the compromise between precision and accuracy in a many-particle system; both will continue to improve as the number of particles increases.

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).

We investigate the influence of atomic motion on precision Rabi spectroscopy of ultracold fermionic atoms confined in a deep one-dimensional optical lattice. We analyze the spectral components of longitudinal sideband spectra and present a model to extract information about the transverse motion and sample temperature from their structure. Rabi spectroscopy of the clock transition itself is also influenced by atomic motion in the weakly confined transverse directions of the optical lattice. By deriving Rabi flopping and Rabi line shapes of the carrier transition, we obtain a model to quantify trap-state-dependent excitation inhomogeneities. The inhomogeneously excited ultracold fermions become distinguishable, which allows s-wave collisions. We derive a detailed model of this process and explain observed density shift data in terms of a dynamic meanfield shift of the clock transition.

At ultracold temperatures, the Pauli exclusion principle suppresses collisions between identical fermions. This has motivated the development of atomic clocks with fermionic isotopes. However, by probing an optical clock transition with thousands of lattice-confined, ultracold fermionic strontium atoms, we observed density-dependent collisional frequency shifts. These collision effects were measured systematically and are supported by a theoretical description attributing them to inhomogeneities in the probe excitation process that render the atoms distinguishable. This work also yields insights for zeroing the clock density shift.

We present a unifying theoretical framework that describes recently observed many-body effects during the interrogation of an optical lattice clock operated with thousands of fermionic alkaline earth atoms. The framework is based on a many-body master equation that accounts for the interplay between elastic and inelastic p-wave and s-wave interactions, finite temperature effects and excitation inhomogeneity during the quantum dynamics of the interrogated atoms. Solutions of the master equation in different parameter regimes are presented and compared. It is shown that a general solution can be obtained by using the so called Truncated Wigner Approximation which is applied in our case in the context of an open quantum system. We use the developed framework to model the density shift and decay of the fringes observed during Ramsey spectroscopy in the JILA 87 Sr and NIST 171 Yb optical lattice clocks. The developed framework opens a suitable path for dealing with a variety of strongly-correlated and driven open-quantum spin systems.arXiv:1310.5248v2 [cond-mat.quant-gas]

Copyright and reuse:Sussex Research Online is a digital repository of the research output of the University.Copyright and all moral rights to the version of the paper presented here belong to the individual author(s) and/or other copyright owners. To the extent reasonable and practicable, the material made available in SRO has been checked for eligibility before being made available.Copies of full text items generally can be reproduced, displayed or performed and given to third parties in any format or medium for personal research or study, educational, or not-for-profit purposes without prior permission or charge, provided that the authors, title and full bibliographic details are credited, a hyperlink and/or URL is given for the original metadata page and the content is not changed in any way. We discuss in detail the search for a permanent electric dipole moment (EDM) of the 199 Hg atom reported by Griffith et al. [Phys. Rev. Lett. 102, 101601 (2009)]. The upper bound, d( 199 Hg) < 3.1 × 10 −29 e cm (95% C.L.), is a factor of 7 improvement over the best previous EDM limit for 199 Hg, provides the most sensitive probe to date for EDMs in diamagnetic atoms, and sets new limits on time-reversal symmetry violation in extensions to the standard model. This paper provides extensive discussion of the techniques used to search for the 199 Hg EDM and the implications of the new 199 Hg EDM limit for CP violation in elementary particle interactions.