Session U6: Hot Topics

Atom Trap Trace Analysis

Since the invention of radiocarbon dating in 1949, trace analyses of long-lived cosmogenic isotopes have contributed to a wide range of scientific and technological areas. We have developed an analytical method called Atom Trap Trace Analysis (ATTA), in which individual atoms of the desired isotope are selectively captured and detected with a magneto-optical trap. ATTA possesses a superior selectivity and is used to analyze environmental radio-isotopes: $^{81}$Kr, $^{85}$Kr, and $^{39}$Ar. These three isotopes have extremely low isotopic abundances in the range of 10$^{-16} - 10^{-11}$, and cover a wide range of ages and applications. This work is supported by DOE, Office of Nuclear Physics, and by NSF, Division of Earth Sciences.   

Improved Measurement of the Electron EDM

The electron is predicted to be slightly aspheric,\footnote{I. B. Khriplovich, S. K. Lamoreaux, CP Violation Without Strangeness (Springer, New York, 1997).} though no experiment has ever observed this deviation. Comparing the measured and predicted shape provides a powerful test of the standard model of particle physics. The shape is also intimately related to one of the largest outstanding questions in cosmology: why is the universe almost entirely devoid of antimatter? The electron's shape can be characterised by its electric dipole moment (EDM), $d_e$, which measures the deviation of its electric interactions from purely spherical. According to the standard model, this EDM is $d_e \approx 10^{-38}$ e.cm -- some eleven orders of magnitude below the current experimental limit. Most extensions to the standard model predict much larger values, potentially accessible to measurement.\footnote{E. D. Commins, Electric dipole moments of leptons, in Advances in Atomic, Molecular, and Optical Physics, Vol. 40, B. Bederson and H.Walther (Eds.), Academic Press, New York, pp. 1-56 (1999).} Hence, the search for the electron EDM is a search for physics beyond the standard model. Moreover, a non-zero breaks time-reversal symmetry which, in many models of particle physics, is equivalent to breaking the symmetry between matter and antimatter, known as CP symmetry. New CP-breaking physics is thought to be needed to explain the existence of a material universe.\footnote{A. D. Sakharov, Violation of CP invariance, C asymmetry, and baryon asymmetry of the universe, Pis'ma ZhETF 5, 32 (1967). *Sov. Phys. JETP Lett. 5, 24 (1967).]} We have used cold, polar molecules to measure the electron EDM, obtaining the result $d_e = (-2.4 \pm 5.7_{stat} \pm 1.5_{syst}) \times 10^{-28}$ e.cm. We set a new upper limit of with 90\% confidence. Our result, consistent with zero, indicates that the electron is spherical at this improved level of precision. Our measurement, of atto-eV energy shifts in a molecule, probes new physics at the tera-eV energy scale. Many extensions to the standard model, such as the minimal supersymmetric standard model, naturally predict large EDMs and our measurement places significant constraints on the parameters of these theories.\footnote{E. D. Commins and D. DeMille, ``The electric dipole moment of the electron,'' Chapter 14 in Lepton Dipole Moments Eds. B. L. Roberts and W. J. Marciano, (World Scientific, Singapore 2010).}   

Sequential Double Ionization: The Timing of Release

The timing of electron release in strong field double ionization poses great challenges both for conceptual definition and for conducting experimental measurement. Here we present coincidence momentum measurements of the doubly charged ion and of the two electrons arising from double ionization of Argon using elliptically (close to circularly) polarized laser pulses [1]. Based on a semi-classical model, the ionization times are calculated from the measured electron momenta across a large intensity range. Exploiting the attoclock technique [2] we have direct access to timings on a coarse and on a fine scale, similar to the hour and the minute hand of a clock. In our attoclock, the magnitude of the electron momenta follows the envelope of the laser pulse and gives a coarse timing for the electron releases (the hour hand), while the fine timing (the minute hand) is provided by the emission angle of the electrons. The first of our findings is that due to depletion the averaged ionization time moves towards the beginning of the pulse with increasing intensity, confirming the results of Maharjan et al. [3], and that the ion momentum distribution projected onto the minor polarization axis shows a bifurcation from a 3-peak to a 4-peak structure. This effect can be fully understood by modeling the process semi-classically in the independent electron approximation following the simple man's model [4]. The ionization time measurement performed with the attoclock shows that the release time of the first electron is in good agreement with the semi-classical simulation performed on the basis of Sequential Double Ionization (SDI), whereas the ionization of the second electron occurs significantly earlier than predicted. This observation suggests that electron correlation and other Non-Sequential Double Ionization (NSDI) mechanisms may play an important role also in the case of strong field double ionization by close-to-circularly polarized laser pulses.\\[4pt] [1] A. N. Pfeiffer et al., Nat. Phys., DOI: 10.1038/NPHYS1946.\\[0pt] [2] P. Eckle et al., Nat. Phys. \textbf{4}, 565 (2008).\\[0pt] [3] C. M. Maharjan et al., Phys. Rev. A \textbf{72}, 041403 (2005).\\[0pt] [4] P. B. Corkum, Phys. Rev. Lett. \textbf{71}, 1994 (1993).   

14-qubit entanglement: creation and coherence

We report the creation of multiparticle entangled states with up to 14 qubits. By investigating the coherence of up to 8 ions over time, we observe a decay proportional to the square of the number of qubits. The observed decay agrees with a theoretical model which assumes a system affected by correlated, Gaussian phase noise. This model holds for the majority of current experimental systems developed towards quantum computation and quantum metrology.