Benjamin Geoffrey Norton

Imaging of Trapped Ions with a Microfabricated Optic for Quantum Information Processing

Trapped ions are a leading system for realizing quantum information processing (QIP). Most of the technologies required for implementing large-scale trapped-ion QIP have been demonstrated, with one key exception: a massively parallel ion-photon interconnect. Arrays of microfabricated phase Fresnel lenses (PFL) are a promising interconnect solution that is readily integrated with ion trap arrays for large-scale QIP. Here we show the first imaging of trapped ions with a microfabricated in-vacuum PFL, demonstrating performance suitable for scalable QIP. A single ion fluorescence collection efficiency of 4.2±1.5% was observed. The depth of focus for the imaging system was 19.4±2.4 μm and the field of view was 140±20 μm. Our approach also provides an integrated solution for high-efficiency optical coupling in neutral atom and solid-state QIP architectures.

Absorption imaging of a single atom

Absorption imaging has played a key role in the advancement of science from van Leeuwenhoeks discovery of red blood cells to modern observations of dust clouds in stellar nebulas and Bose-Einstein condensates. Here we show the first absorption imaging of a single atom isolated in a vacuum. The optical properties of atoms are thoroughly understood, so a single atom is an ideal system for testing the limits of absorption imaging. A single atomic ion was confined in an RF Paul trap and the absorption imaged at near wavelength resolution with a phase Fresnel lens. The observed image contrast of 3.1 (3)% is the maximum theoretically allowed for the imaging resolution of our set-up. The absorption of photons by single atoms is of immediate interest for quantum information processing. Our results also point out new opportunities in imaging of light-sensitive samples both in the optical and X-ray regimes.

Wavelength-scale imaging of trapped ions using a phase Fresnel lens

A microfabricated phase Fresnel lens was used to image ytterbium ions trapped in a radio frequency Paul trap. The ions were laser cooled close to the Doppler limit on the 369.5 nm transition, reducing the ion motion so that each ion formed a near point source. By detecting the ion fluorescence on the same transition, near-diffraction-limited imaging with spot sizes of below 440 nm (FWHM) was achieved. To our knowledge, this is the first demonstration of wavelength-scale imaging of trapped ions and the highest imaging resolution ever achieved with atoms in free space.

Millikelvin spatial thermometry of trapped ions

We demonstrate millikelvin thermometry of laser-cooled trapped ions with high-resolution imaging. This equilibrium approach is independent of the cooling dynamics and has lower systematic error than Doppler thermometry, with ±5mK accuracy and ±1mK precision. We used it to observe the highly anisotropic dynamics of a single ion,finding temperatures of 15K simultaneously along different directions. This thermometry technique can offer new insights into quantum systems sympathetically cooled by ions, including atoms, molecules, nanomechanical oscillators and electric circuits. Laser-cooled trapped ions are a nearly ideal system for investigation of quantum physics. The internal ion states are strongly decoupled from the surrounding environment and can exhibit coherence times of many seconds. In ultrahigh vacuum the motions of the ions are strongly coupled together, but otherwise exhibit good immunity to external perturbations. Precision manipulation of ions at the quantum level is readily achieved through the use of lasers and electromagnetic fields. These properties have made laser-cooled trapped ions a preferred platform for implementing experiments in quantum information processing (QIP) (1-4) and precision metrology (5, 6). The strong Coulomb coupling makes laser-cooled trapped ions attractive for sympathetic cooling at millikelvin temperatures in investigations of fundamental physics (7), dynamics of complex molecular (8, 9) and biomolecular (10) ions, nano-mechanical oscillators (11, 12), resonant electric circuits (13) and Bose-Einstein condensates (14). Millikelvin thermometry is a key diagnostic in all these experiments. Cooling near the Doppler limit, 1mK, is a precondition for studies of quantum dynamics and precision measurements. Millikelvin thermometry is crucial for quantifying the effectiveness of Doppler

An automated submicron beam profiler for characterization of high numerical aperture optics.

The focusing properties of three aspheric lenses with numer ical aperture (NA) between 0.53 and 0.68 were directly measured u sing an interferometrically referenced scanning knife-edge beam profiler with sub-micron resolution. The results obtained for two of the t ree lenses tested were in agreement with paraxial gaussian beam theory . It was also found that the highest NA aspheric lens which was designed fo r 830nm was not diffraction limited at 633nm. This process was autom ated using motorized translation stages and provides a direct method f or testing the design specifications of high numerical aperture optics.

Scalable ion–photon quantum interface based on integrated diffractive mirrors

Quantum networking links quantum processors through remote entanglement for distributed quantum information processing and secure long-range communication. Trapped ions are a leading quantum information processing platform, having demonstrated universal small-scale processors and roadmaps for large-scale implementation. Overall rates of ion–photon entanglement generation, essential for remote trapped ion entanglement, are limited by coupling efficiency into single mode fibers and scaling to many ions. Here, we show a microfabricated trap with integrated diffractive mirrors that couples 4.1(6)% of the fluorescence from a 174Yb+ ion into a single mode fiber, nearly triple the demonstrated bulk optics efficiency. The integrated optic collects 5.8(8)% of the π transition fluorescence, images the ion with sub-wavelength resolution, and couples 71(5)% of the collected light into the fiber. Our technology is suitable for entangling multiple ions in parallel and overcomes mode quality limitations of existing integrated optical interconnects.Quantum computing: high-resolution optics built directly into a micro-fabricated ion trapBuilding large-scale quantum computers or distributed networks of quantum computers requires small-scale nodes to be readily replicated and effectively connected. Atomic ions trapped above the surface of micro-fabricated chips are a leading method for implementing small, scalable, stationary quantum processing nodes. External communication between trapped ions has previously required bulky multi-element optics to create efficient photonic interconnections through single-mode optical fibers. Moji Ghadimi, with colleagues at Griffith University (Australia) and GeorgiaTech Research Institute, have overcome this hurdle with a demonstration of a chip trap with the primary optic integrated directly onto its surface. By patterning the flat reflective surface of the chip trap with a computer-generated hologram of a perfect focusing mirror they were able to image the ion’s fluorescence with nearly no distortions and couple that light efficiently into a single-mode fiber. This approach transfers optical complexity into the chip trap fabrication, where it can be more easily mass-produced.

A single-atom 3D sub-attonewton force sensor

We realize a 3D force sensor through super-resolution imaging of a single trapped ion and measured a 95-zN light force. Forces drive all physical interactions. High-sensitivity measurement of the effect of forces enables the quantitative investigation of physical phenomena. Laser-cooled trapped atomic ions are a well-controlled quantum system whose low mass, strong Coulomb interaction, and readily detectable fluorescence signal make them a favorable platform for precision metrology. We demonstrate a three-dimensional sub-attonewton sensitivity force sensor based on a super-resolution imaging of a single trapped ion. The force is detected by measuring the ion’s displacement in three dimensions with nanometer precision. Observed sensitivities were 372 ± 9, 347 ± 18, and 808 ± 51 zN/Hz, corresponding to 24×, 87×, and 21× above the quantum limit. We verified this technique by measuring a 95-zN light pressure force, an important systematic effect in optically based sensors.

Single atom sub atto-newton force sensor in three-dimensions

Ultra-sensitive force measurements are crucial for physics. Nanometer precision displacement measurements of a Paul trapped ¹⁷⁴Yb⁺ ion provides force sensitivities below aN/√Hz. Accuracy was verified by measuring the 95 zN cooling laser light force pressure.

Integrated Fresnel Mirrors for scalable trapped ion quantum computing

Photonic interconnects are a bottleneck to achieving large-scale trapped ion quantum computing. We fabricated a surface trap with diffractive mirrors and achieved sub-wavelength imaging of a trapped ion and 2.0±0.5% coupling into a single-mode fiber.

Scalable trapped-ion single-photon sources with monolithically integrated optics

We demonstrate the first fully integrated and scalable diffractive mirrors for efficient ion light collection. We also generated single photons using an Yb+ ion and collected them using these mirrors to do a quantum communication protocol.