Harley Hayden

Demonstration of integrated microscale optics in surface-electrode ion traps

In ion trap quantum information processing, efficient fluorescence collection is critical for fast, high-fidelity qubit detection and ion–photon entanglement. The expected size of future many-ion processors requires scalable light collection systems. We report on the development and testing of a microfabricated surface-electrode ion trap with an integrated high-numerical aperture (NA) micromirror for fluorescence collection. When coupled to a low-NA lens, the optical system is inherently scalable to large arrays of mirrors in a single device. We demonstrate the stable trapping and transport of 40Ca+ ions over a 0.63 NA micromirror and observe a factor of 1.9 enhancement of photon collection compared to the planar region of the trap.

Reliable transport through a microfabricated X-junction surface-electrode ion trap

We report the design, fabrication and characterization of a micro- fabricated surface-electrode ion trap that supports controlled transport through the two-dimensional intersection of linear trapping zones arranged in a 90 cross. The trap is fabricated with very large scalable integration techniques which are compatible with scaling to a large quantum information processor. The shape of the radio-frequency electrodes is optimized with a genetic algorithm to reduce axial pseudopotential barriers and minimize ion heating during transport. Seventy-eight independent dc control electrodes enable fine control of the trapping potentials. We demonstrate reliable ion transport between junction legs and determine the rate of ion loss due to transport. Doppler-cooled ions survive more than 10 5 round-trip transits between junction legs without loss and more than 65 consecutive round trips without laser cooling.

Controlling trapping potentials and stray electric fields in a microfabricated ion trap through design and compensation

Recent advances in quantum information processing with trapped ions have demonstrated the need for new ion trap architectures capable of holding and manipulating chains of many (>10) ions. Here we present the design and detailed characterization of a new linear trap, microfabricated with scalable complementary metal-oxide-semiconductor (CMOS) techniques, that is well-suited to this challenge. Forty-four individually controlled dc electrodes provide the many degrees of freedom required to construct anharmonic potential wells, shuttle ions, merge and split ion chains, precisely tune secular mode frequencies, and adjust the orientation of trap axes. Microfabricated capacitors on dc electrodes suppress radio-frequency pickup and excess micromotion, while a top-level ground layer simplifies modeling of electric fields and protects trap structures underneath. A localized aperture in the substrate provides access to the trapping region from an oven below, permitting deterministic loading of particular isotopic/elemental sequences via species-selective photoionization. The shapes of the aperture and radio-frequency electrodes are optimized to minimize perturbation of the trapping pseudopotential. Laboratory experiments verify simulated potentials and characterize trapping lifetimes, stray electric fields, and ion heating rates, while measurement and cancellation of spatially-varying stray electric fields permits the formation of nearly-equally spaced ion chains.

Multiscale optics for enhanced light collection from a point source

High-efficiency collection of photons emitted by a point source over a wide field of view (FoV) is crucial for many applications. Multiscale optics offer improved light collection by utilizing small optical components placed close to the optical source, while maintaining a wide FoV provided by conventional imaging optics. In this work, we demonstrate collection efficiency of 26% of photons emitted by a pointlike source using a micromirror fabricated in silicon with no significant decrease in collection efficiency over a 10 mm object space.

Spatially uniform single-qubit gate operations with near-field microwaves and composite pulse compensation

We present a microfabricated surface-electrode ion trap with a pair of integrated waveguides that generate a standing microwave field resonant with the 171 Yb + hyperfine qubit. The waveguides are engineered to position the wave antinode near the center of the trap, resulting in maximum field amplitude and uniformity along the trap axis. By calibrating the relative amplitudes and phases of the waveguide currents, we can control the polarization of the microwave field to reduce off-resonant coupling to undesired Zeeman sublevels. We demonstrate single-qubit -rotations as fast as 1µs with less than 6% variation in Rabi frequency over an 800µm microwave interaction region. Fully compensating pulse sequences further improve the uniformity of X-gates across this interaction region.

In-vacuum active electronics for microfabricated ion traps

The advent of microfabricated ion traps for the quantum information community has allowed research groups to build traps that incorporate an unprecedented number of trapping zones. However, as device complexity has grown, the number of digital-to-analog converter (DAC) channels needed to control these devices has grown as well, with some of the largest trap assemblies now requiring nearly one hundred DAC channels. Providing electrical connections for these channels into a vacuum chamber can be bulky and difficult to scale beyond the current numbers of trap electrodes. This paper reports on the development and testing of an in-vacuum DAC system that uses only 9 vacuum feedthrough connections to control a 78-electrode microfabricated ion trap. The system is characterized by trapping single and multiple (40)Ca(+) ions. The measured axial mode stability, ion heating rates, and transport fidelities for a trapped ion are comparable to systems with external (air-side) commercial DACs.

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.

Nanomagnetic films and arrays for nonlinear devices in highly-integrated RF modules

Magnetic materials have traditionally faced several limitations for RF and power applications because of their unstable permeability with frequency and electric field. However, the same attributes of these materials, when designed at nanoscale, enable interesting nonlinear properties for applications as frequency-selective limiters and signal-to-noise enhancers. Anisotropic nanostructures also enhance frequency stability. This paper explores nanomagnetic arrays for such ultra-miniaturized RF components in multimode and multiband (MMMB) RF modules. Permalloy films and nanodot arrays were modeled for their frequency-response to assess their nonlinear properties. By designing the dimensions at nanoscale, field-dependent permeability spectra were obtained using micromagnetic simulations. Permalloy thinfilm and nanodot arrays were fabricated on silicon substrates using e-beam evaporation and e-beam nanolithography. The simulation results for blanket films were validated by characterizing the permeability spectra using strip-line structures. Results indicate that nanomagnetic films and arrays can be used to create nonlinear devices as building blocks for a variety of highly-integrated RF modules.

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.