Measurement Of Parity Nonconservation Research Articles

Measurement of the electric quadrupole amplitude in atomic thallium transition using electromagnetically induced transparency

We report on a measurement of the transition amplitude ratio χ of an electric quadrupole () to a magnetic dipole () of the transition in atomic thallium. We utilized the electromagnetically induced transparency mechanism and the sideband-bridging technique to resolve the isotopic transitions and their hyperfine manifold. Our measurement gave for 205Tl, and for 203Tl, which was measured for the first time. Our results provide a reference point for the theoretical calculation of atomic structures, and new input for the long dispute on the atomic thallium parity non-conservation measurements.

Studies of the weak interaction in atomic systems: towards measurements of atomic parity non-conservation in francium

Tests of the standard model of particle physics should be carried out over the widest possible range of energies. Here we present our plans and progress for an atomic parity non-conservation experiment using the heaviest alkali, francium (Z = 87), which has no stable isotope. Low-energy tests of this kind have sensitivity complementary to higher energy searches, e.g. at the large hadron collider.

Observation of the 87Rb 5S1/2 to 4D3/2 electric quadrupole transition at 516.6 nm mediated via an optical nanofibre

Light guided by an optical nanofibre has a very steep evanescent field gradient extending from the fibre surface. This gradient can be exploited to drive electric quadrupole transitions in nearby quantum emitters. In this paper, we report on the observation of the 5S1/2 → 4D3/2 electric quadrupole transition at 516.6 nm (in vacuum) in laser-cooled 87Rb atoms using only a few μW of laser power propagating through an optical nanofibre embedded in the atom cloud. This work extends the range of applications for optical nanofibres in atomic physics to include more fundamental tests such as high-precision measurements of parity non-conservation.

Determination of the Scalar and Vector Polarizabilities of the Cesium 6s^{2}S_{1/2}→7s^{2}S_{1/2} Transition and Implications for Atomic Parity Nonconservation.

Using recent high-precision measurements of electric dipole matrix elements of atomic cesium, we make an improved determination of the scalar (α) and vector (β) polarizabilities of the cesium 6s^{2}S_{1/2}→7s^{2}S_{1/2} transition calculated through a sum-over-states method. We report values of α=-268.82(30)a_{0}^{3} and β=27.139(42)a_{0}^{3} with the highest precision to date. We find a discrepancy between our value of β and the past preferred value, resulting in a significant shift in the value of the weak charge Q_{w} of the cesium nucleus. Future work to resolve the differences in the polarizability will be critical for interpretation of parity nonconservation measurements in cesium, which have implications for physics beyond the standard model.

Efficient inter-trap transfer of cold francium atoms

We report on the status of the FrPNC experiments and summarize our plans for measurements of parity non-conservation (PNC) in a sample of cold francium. The FrPNC collaboration has commissioned a laser cooling apparatus at the TRIUMF accelerator that collects and cools francium atoms for PNC experiments. We have recently demonstrated the robust, high efficiency transfer (50 %) of laser cooled francium atoms to a second laser cooling apparatus, located 0.7 m below the first, where the PNC experiments will be conducted.

High steady-state column density of I((2)P3/2) atoms from I2 photodissociation at 532 nm: Towards parity non-conservation measurements.

Steady-state column densities of 1017 cm−2 of I(2P3/2) atoms are produced from photodissociation of I2 vapour at 290.5 K using 5 W of 532 nm laser light. Recombination of the I(2P3/2) atoms at the cell walls is minimized by coating the cell surface with a hydrophobic silane (dimethyldichlorosilane/DMDCS). Operation at room temperature, and at an I2 vapour pressure of ~0.2 mbar, without using a buffer gas, allows relatively low Lorentz and Doppler widths of ~2π × 1.5 (FWHM) and ~2π × 150 (HW at 1/e2) Mrad/s, respectively, at the M1 transition of atomic iodine at 1315 nm. These high column densities and low linewidths are favorable for parity nonconservation optical rotation measurements near this M1 transition. Furthermore, as the cell is completely sealed, this method of production of high-density 127I(2P3/2) atoms is also compatible with using iodine radioisotopes, such as for the production of high-density 129I(2P3/2).

Theoretical studies of the long lifetimes of the6dD3/2,5/22states in Fr: Implications for parity-nonconservation measurements

Lifetimes of the $6d^{2}D_{3/2}$ and $6d^{2}D_{5/2}$ states in Fr are determined from calculations of the radiative transition amplitudes of the allowed electric dipole $(E1)$ and the forbidden electric quadrupole $(E2)$ and magnetic dipole $(M1)$ channels which were performed using the second-order many-body perturbation theory and the coupled-cluster method at different levels of approximations in the relativistic framework. The values obtained for these two quantities are 540(10) and 1704(32) ns, respectively. These relatively long lifetimes and the large electric dipole parity-non-conserving amplitudes of $7s^{2}S_{1/2}\ensuremath{\rightarrow}6d^{2}D_{3/2,5/2}$ transitions strongly favor Fr as a leading candidate for the measurement of parity nonconservation arising from the neutral-current weak interaction and the nuclear anapole moment. In another important application, these $6D$ states in Fr can be used efficiently for resonance ionization spectroscopic techniques to carry out precise measurements of the properties of the higher excited states due to the long lifetimes of these states.

Noise-immune cavity-enhanced optical heterodyne molecular spectrometry on N₂O 1.283 μm transition based on a quantum-dot external-cavity diode laser.

To access the wavelength within the 1.1-1.3 μm region, we have developed a quantum-dot (QD) laser with an external-cavity configuration and a linewidth of kilohertz at a 1 ms integration time. The residual electroluminescence, due to the inhomogeneous broadening of the QD gain medium, was observed and filtered out using a grating. While a fiber-coupled electro-optical modulator was employed, this laser system was locked to a high-finesse (F∼18,500) optical cavity, and noise-immune cavity-enhanced optical heterodyne molecular spectroscopy was used to observe weak transitions. The Doppler-broadened spectra of a weak N(2)O transition at 1.283 μm are obtained with a signal-to-noise ratio of 30 for a gas pressure of 54 mTorr. The minimum noise-equivalent absorption coefficient is 5.3×10(-10) cm(-1) Hz(-1/2). This system can be a powerful and stable light source for atomic parity nonconservation measurements using thallium, ytterbium, lead, and iodine.

Offline trapping of 221Fr in a magneto-optical trap from implantation of an 225Ac ion beam

We demonstrate a new technique to prepare an offline source of francium for trapping in a magneto-optical trap. Implanting a radioactive beam of 225Ac, t1/2 = 9.920(3) days, in a foil, allows use of the decay products, i.e. 221Fr, t1/2 = 288.0(4) s. 221Fr is ejected from the foil by the α decay of 225Ac. This technique is compatible with the online accumulation of a laser-cooled atomic francium sample for a series of planned parity non-conservation measurements at TRIUMF. We obtain a 34 % release efficiency for 221Fr from the recoil source based on particle detector measurements. We find that laser cooling operation with the source is 8+10-5 times less efficient than from a mass-separated ion beam of 221Fr in the current geometry. While the flux of this source is two to three orders of magnitude lower than typical francium beams from ISOL facilities, the source provides a longer-term supply of francium for offline studies.

Measurement of the Stark shift of the6s2S1/2→7p2PJtransitions in atomic cesium

We report measurements of the Stark shift of the cesium $6s \: ^2S_{3/2} \rightarrow 7p \: ^2P_{3/2} $ and the $6s \: ^2S_{1/2} \rightarrow 7p \: ^2P_{1/2} $ transitions at $\lambda = 456$ nm and 459 nm, respectively, in an atomic beam. From these, we determine the static scalar polarizability for both 7P states, and the tensor polarizability for the 7P$_{3/2}$ state. The fractional uncertainty of the scalar polarizabilites is $\sim$0.18\%, while that of the tensor term is 0.66\%. These measurements provide sensitive tests of theoretical models of the Cs atom, which has played a central role in parity nonconservation measurements.

Commissioning of the Francium Trapping Facility at TRIUMF

We report on the successful commissioning of the Francium Trapping Facility at TRIUMF. Large laser-cooled samples of francium are produced from a francium ion beam delivered by the ISAC radioactive ion beam facility. The ion beam is neutralized on an yttrium foil, which is subsequently heated to transfer the atoms into the magneto-optical trapping region. We have successfully trapped 207Fr, 209Fr and 221Fr, with a maximum of 2.5 × 105 209Fr atoms. The neutral cold atoms will be used in studies of the weak interaction through measurements of atomic parity non-conservation.

Calculation of strongly forbiddenM1transitions andg-factor anomalies in atoms considered for parity-nonconservation measurements

We calculate magnetic dipole transition amplitudes in s-s and s-d transitions of Rb, Cs, Ba+, Fr, Ra+, Yb+, Ac2+ and Th3+. These transitions were used or considered to be used for the measurements of parity non-conservation (PNC). We also calculate the magnetic g-factor anomalies for a selection of states, along with electric quadrupole transition amplitudes for s-d transitions in these systems.

Method for measuring the6S1/2↔5D3/2magnetic-dipole-transition moment in Ba+

We propose a method for measuring the magnetic dipole ($M1$) transition moment of the $6{S}_{1/2}(m=\ensuremath{-}1/2)\ensuremath{\leftrightarrow}5{D}_{3/2}(m=\ensuremath{-}1/2)$ transition in single trapped Ba${}^{+}$ by exploiting different symmetries in the electric quadrupole ($E2$) and $M1$ couplings between the states. The technique is adapted from a previously proposed method for measuring atomic parity nonconservation in a single trapped ion [N. Fortson, Phys. Rev. Lett. 70, 2383 (1993)]. Knowledge of $M1$ is crucial for any parity nonconservation measurement in Ba${}^{+}$, as laser coupling through $M1$ can mimic the parity-violating signal. The magnetic moment for the transition has been calculated by atomic theory and found to be dominated by electron-electron correlation effects [B. K. Sahoo et al., Phys. Rev. A 74, 062504 (2006)]. To date the value has not been verified experimentally. This proposed measurement is therefore an essential step toward a parity nonconservation experiment in the ion that will also test current many-body theory. The technique can be adapted for similar parity nonconservation experiments using other atomic ions, where the magnetic dipole moment could present similar complications.

Calculation of the parity-violating 5s-6sE1 amplitude in the rubidium atom

Currently, the theoretical uncertainty limits the interpretation of the atomic parity-nonconservation (PNC) measurements. We calculate the PNC $5s$-$6s$ electric dipole transition amplitude in rubidium and demonstrate that rubidium is a good candidate to search for new physics beyond the standard model since accuracy of the atomic calculations in rubidium can be higher than in cesium. PNC in cesium is currently the best low-energy test of the standard model; therefore, similar measurements for rubidium present a good option for further progress in the field. We also calculate the nuclear spin-dependent part of the PNC amplitude, which is needed for the extraction of the nuclear anapole moment from the PNC measurements.

Revisiting Parity Nonconservation in Cesium

We apply the sum-over-states approach to calculate partial contributions to parity nonconservation (PNC) in cesium [Porsev, Beloy, and Drevianko, Phys. Rev. Lett. 102, 181601 (2009)]. We find significant corrections to two nondominating terms coming from the contribution of the core and highly excited states (n>9, the so called tail). When these differences are taken into account the result of Porsev et al., E(PNC)=0.8906(24)×10(-11)i(-Q(W)/N) changes to 0.8977 (40), coming into good agreement with our previous calculations, 0.8980 (45). The interpretation of the PNC measurements in cesium still indicates reasonable agreement with the standard model (1.5σ); however, it gives new constraints on physics beyond it.

Sensitivity test of a blue-detuned dipole trap designed for parity non-conservation measurements in Fr

A dynamic blue-detuned optical dipole trap with stable (87)Rb atoms produces a differential ac Stark shift of 18 Hz in the ground state hyperfine transition, and it preserves the ground state hyperfine superpositions for a long coherence time of 180 ms. The trapped atoms undergoing microwave Rabi oscillations are sensitive to a small signal, artificially generated with a second microwave source, phase locked to the first allowing a simple and effective method for determining signal-to-noise ratio limits through interference techniques. This provides an excellent means of calibrating sensitivity in experiments such as our ongoing Fr parity non-conservation measurement.

Single-ion quantum lock-in amplifier

Quantum metrology uses tools from quantum information science to improve measurement signal-to-noise ratios. The challenge is to increase sensitivity while reducing susceptibility to noise, tasks that are often in conflict. Lock-in measurement is a detection scheme designed to overcome this difficulty by spectrally separating signal from noise. Here we report on the implementation of a quantum analogue to the classical lock-in amplifier. All the lock-in operations--modulation, detection and mixing--are performed through the application of non-commuting quantum operators to the electronic spin state of a single, trapped Sr(+) ion. We significantly increase its sensitivity to external fields while extending phase coherence by three orders of magnitude, to more than one second. Using this technique, we measure frequency shifts with a sensitivity of 0.42 Hz Hz(-1/2) (corresponding to a magnetic field measurement sensitivity of 15 pT Hz(-1/2)), obtaining an uncertainty of less than 10 mHz (350 fT) after 3,720 seconds of averaging. These sensitivities are limited by quantum projection noise and improve on other single-spin probe technologies by two orders of magnitude. Our reported sensitivity is sufficient for the measurement of parity non-conservation, as well as the detection of the magnetic field of a single electronic spin one micrometre from an ion detector with nanometre resolution. As a first application, we perform light shift spectroscopy of a narrow optical quadrupole transition. Finally, we emphasize that the quantum lock-in technique is generic and can potentially enhance the sensitivity of any quantum sensor.

Fundamental symmetries studies with cold trapped francium atoms at ISAC

Francium combines a heavy nucleus (Z = 87) with the simple atomic structure of alkalis and is a very promising candidate for precision tests of fundamental symmetries such as atomic parity non-conservation measurements. Fr has no stable isotopes, and the ISAC radioactive beam facility at TRIUMF, equipped with an actinide target, promises to provide record quantities of Fr atoms, up to 1010/s for some isotopes. We discuss our plans for a Fr on-line laser trapping facility at ISAC and experiments with samples of cold Fr atoms. We outline our plans for a measurement of the nuclear anapole moment — a parity non-conserving, time-reversal conserving moment that arises from weak interactions between nucleons — in a chain of Fr isotopes. Its measurement is a unique probe for neutral weak interactions inside the nucleus.

PRECISION MEASUREMENTS OF PARITY VIOLATION AND THE WEAK MIXING ANGLE IN MØLLER SCATTERING

We report an observation of a parity-violating asymmetry in fixed target electron-electron (Møller) scattering at a four-momentum transfer Q2 = 0.03 ( GeV/c )2. This is a most precise measurement of parity nonconservation to date, and leads to a determination of the electron's weak charge and of the value of the effective weak mixing angle [Formula: see text], which is consistent with the Standard Model expectation at the current level of precision. The comparison between the measurements of the weak mixing angle at Q2 = 0.03 ( GeV/c )2 and at the Z0 pole establishes the running of sin 2θW with 6.5σ significance.

Measurement of the collisional self-broadening of the cesium6S1∕2→5D3∕2(689−nm)electric quadrupole transition

We have measured the collisional self-broadening of the cesium $6{S}_{1∕2}\ensuremath{\rightarrow}5{D}_{3∕2}$ electric quadrupole $(E2)$ transition at $689\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ for temperatures from $220\phantom{\rule{0.5em}{0ex}}\text{to}\phantom{\rule{0.5em}{0ex}}370\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, corresponding to cesium number densities from $3\ifmmode\times\else\texttimes\fi{}{10}^{15}\phantom{\rule{0.5em}{0ex}}\text{to}\phantom{\rule{0.5em}{0ex}}1.5\ifmmode\times\else\texttimes\fi{}{10}^{17}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$. This $E2$ transition may have utility for studies of atomic parity nonconservation (PNC), and the collisional self-broadening represents an important systematic effect which must be understood for an accurate measurement of PNC. We find a value for this broadening of $1.32\ifmmode\pm\else\textpm\fi{}0.06\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{3}\phantom{\rule{0.2em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$, which is consistent with what would be expected for a quadrupole-quadrupole resonance interaction. To the best of our knowledge, no quantitative measurement of the self-broadening of an atomic $E2$ transition has been reported previously in the literature.