Active Two-dimensional Steering of Radiation from a Nano-Aperture

We experimentally demonstrate control over the direction of radiation of a beam that passes through a square nano-aperture in a metal film. The ratio of the aperture size and the wavelength is such that only three guided modes, each with different spatial symmetries, can be excited. Using a spatial light modulator, the superposition of the three modes can be altered, thus allowing for a controlled variation of the radiation pattern that emanates from the nano-aperture. Robust and stable steering of 9.5 degree in two orthogonal directions was achieved

Improved bounds on Lorentz violation from composite-pulse Ramsey spectroscopy in a trapped ion

In attempts to unify the four known fundamental forces in a single quantum-consistent theory, it is suggested that Lorentz symmetry may be broken at the Planck scale. Here we search for Lorentz violation at the low-energy limit by comparing orthogonally oriented atomic orbitals in a Michelson-Morley-type experiment. We apply a robust radiofrequency composite pulse sequence in the $^2F_{7/2}$ manifold of an Yb$^+$ ion, extending the coherence time from 200 $\mu$s to more than 1 s. In this manner, we fully exploit the high intrinsic susceptibility of the $^2F_{7/2}$ state and take advantage of its exceptionally long lifetime. We match the stability of the previous best Lorentz symmetry test nearly an order of magnitude faster and improve the constraints on the symmetry breaking coefficients to the 10$^{-21}$ level. These results represent the most stringent test of this type of Lorentz violation. The demonstrated method can be further extended to ion Coulomb crystals

Sideband thermometry of ion crystals

Coulomb crystals of cold trapped ions are a leading platform for the realisation of quantum processors and quantum simulations and, in quantum metrology, for the construction of optical atomic clocks and for fundamental tests of the Standard Model. For these applications, it is not only essential to cool the ion crystal in all its degrees of freedom down to the quantum ground state, but also to be able to determine its temperature with a high accuracy. However, when a large ground-state cooled crystal is interrogated for thermometry, complex many-body interactions take place, making it challenging to accurately estimate the temperature with established techniques. In this work we present a new thermometry method tailored for ion crystals. The method is applicable to all normal modes of motion and does not suffer from a computational bottleneck when applied to large ion crystals. We test the temperature estimate with two experiments, namely with a 1D linear chain of 4 ions and a 2D crystal of 19 ions and verify the results, where possible, using other methods. The results show that the new method is an accurate and efficient tool for thermometry of ion crystals.Comment: 12+5 pages, 9+2 figures, Fig.3(b) was correcte

High-accuracy deep-UV ramsey-comb spectroscopy in krypton

In this paper, we present a detailed account of the first precision Ramseycomb spectroscopy in the deep UV. We excite krypton in an atomic beam using pairs of frequency-comb laser pulses that have been amplified to the millijoule level and upconverted through frequency doubling in BBO crystals. The resulting phasecoherent deep-UV pulses at 212.55 nm are used in the Ramsey-comb method to excite the two-photon 4p6 → 4p55p[1/2]0 transition. For the 84Kr isotope, we find a transition frequency of 2829833101679(103) kHz. The fractional accuracy of 3.7 × 10-11 is 34 times better than previous measurements, and also the isotope shifts are measured with improved accuracy. This demonstration shows the potential of Ramsey-comb excitation for precision spectroscopy at short wavelengths

Testing QED with Ramsey-Comb spectroscopy in the deep-UV range

By combining upconversion of amplified frequency comb laser pulses with Ramsey-spectroscopy, we developed deep-UV Ramsey-Comb excitation, leading to highly accurate two-photon spectroscopy in krypton, and molecular hydrogen for testing QED

Tests of fundamental physics using ramsey-comb spectroscopy on the hydrogen molecule

High-precision spectroscopy on simple systems such as atomic hydrogen has reached an unprecedented level of accuracy in recent years [1]. Experimentally determined energy levels are used to test bound-state quantum electrodynamics (QED). However, theoretical values for the energy levels were limited by the uncertainty of experimentally determined parameters such as the proton charge radius (rp). In 2010, the CREMA collaboration performed a spectroscopic measurement on muonic hydrogen. From this, rp was extracted with a ten times higher accuracy but also showed a 5σ discrepancy to the CODATA-2010 value [2]. This so-called proton radius puzzle remains unsolved. A possible solution to this problem can be obtained from measurements in other systems

Sideband Thermometry of Ion Crystals

Coulomb crystals of cold trapped ions are a leading platform for the realization of quantum processors and quantum simulations and, in quantum metrology, for the construction of optical atomic clocks and for fundamental tests of the standard model. For these applications, it is not only essential to cool the ion crystal in all its degrees of freedom down to the quantum ground state but also to be able to determine its temperature with a high accuracy. However, when a large ground-state cooled crystal is interrogated for thermometry, complex many-body interactions take place, making it challenging to accurately estimate the temperature with established techniques. In this work, we present a new thermometry method tailored for ion crystals. The method is applicable to all normal modes of motion and does not suffer from a computational bottleneck when applied to large ion crystals. We test the temperature estimate with two experiments, namely with a one-dimensional linear chain of four ions and a two-dimensional crystal of 19 ions and verify the results, where possible, using other methods. The results show that the new method is an accurate and efficient tool for thermometry of ion crystals