Nathan Kurz

Trapped ion imaging with a high numerical aperture spherical mirror

Efficient collection and analysis of trapped ion qubit fluorescence is essential for robust qubit state detection in trapped ion quantum computing schemes. We discuss simple techniques of improving photon collection efficiency using high numerical aperture (N.A.) reflective optics. To test these techniques we placed a spherical mirror with an effective N.A. of about 0.9 inside a vacuum chamber in the vicinity of a linear Paul trap. We demonstrate stable and reliable trapping of single barium ions, in excellent agreement with our simulations of the electric field in this setup. While a large N.A. spherical mirror introduces significant spherical aberration, the ion image quality can be greatly improved by a specially designed aspheric corrector lens located outside the vacuum system. Our simulations show that the spherical mirror/corrector design is an easy and cost-effective way to achieve high photon collection rates when compared to a more sophisticated parabolic mirror setup.

Efficient fluorescence collection from trapped ions with an integrated spherical mirror

aberrationscausedbythesphericalmirrorcanbecompensated with optics located outside the vacuum chamber. In this article we demonstrate and characterize the performanceofasphericalmirrorwithaneffectiveNAofatleast0.6, limited only by the linear quarupole trap geometry. We design and implement an aspheric corrector element to reduce the aberrations caused by the spherical mirror. We also suggest a straightforward modification of the trap design to further improve both the image quality and the collection efficiency.

Efficient fluorescence collection and ion imaging with the “tack” ion trap

Trapped, laser-cooled atoms and ions produce intense fluorescence of the order 107~108 photons per second. Detection of this fluorescence enables efficient measurement of the quantum state of qubits based on trapped atoms. It is desirable to collect a large fraction of the photons to make the detection faster and more reliable. Additionally, efficient fluorescence collection can improve the speed and fidelity of remote ion entanglement and quantum gates. Refractive and reflective optics, and optical cavities have all been used to collect the trapped ion fluorescence with up to about 10% efficiency. Here we show a novel ion trap design that incorporates a metallic spherical mirror as the integral part of the trap itself, being its RF electrode. The mirror geometry enables up to 35% solid angle collection of trapped ion fluorescence. The movable central pin electrode of this trap allows precise placement of the ion at the focus of the reflector. We characterize the performance of the mirror, and measure 25% collection efficiency, likely limited by the imperfections of the mirror surface. We also study the properties of the images of single ions formed by the spherical mirror and apply aberration correction with an aspherical element placed outside the vacuum system. Owing to the simplicity of its design, this trap structure can be adapted for microfabrication and integration into more complex trap architectures.Trapped, laser-cooled ions produce intense fluorescence. Detecting this fluorescence enables efficient measurement of quantum state of qubits based on trapped atoms. It is desirable to collect a large fraction of the photons to make the detection faster and more reliable. Additionally, efficient fluorescence collection can improve speed and fidelity of remote ion entanglement and quantum gates. Here we show a novel ion trap design that incorporates metallic spherical mirror as the integral part of the trap itself, being its RF electrode. The mirror geometry enables up to 35% solid angle collection of trapped ion fluorescence; we measure a 25% effective solid angle, likely limited by imperfections of the mirror surface. We also study properties of the images of single ions formed by the mirror and apply aberration correction. Owing to the simplicity of its design, this trap structure can be adapted for micro-fabrication and integration into more complex trap architectures.

Adiabatic passage in the presence of noise

Now add to this Hamiltonian a term that couples the two states, yielding a new Hamiltonian H � . The eigenstates of H � will exhibit an avoided crossing as a function of ω. Consider suchacoupledsysteminitiallyinaneigenstateof H with ω set such that the energy splitting between the states is much larger than the coupling energy. If ω is now varied sufficiently slowly across the energy level crossing, the system will adiabatically

Barium Ions for Quantum Computation

Individually trapped 137Ba+ in an RF Paul trap is proposed as a qubit candidate, and its various benefits are compared to other ionic qubits. We report the current experimental status of using this ion for quantum computation. Future plans and prospects are discussed.

Hyperfine and optical barium ion qubits

State preparation, qubit rotation, and high fidelity readout are demonstrated for two different {sup 137}Ba{sup +} qubit types. First, an optical qubit on the narrow 6S{sub 1/2} to 5D{sub 5/2} transition at 1.76 {mu}m is implemented. Then, leveraging the techniques developed there for readout, a ground-state hyperfine qubit using the magnetically insensitive transition at 8 GHz is accomplished.

Measurement of the branching ratio in the6P3∕2decay ofBaIIwith a single trapped ion

We present a measurement of the branching ratios from the 6P3/2 state of BaII into all dipoleallowed decay channels (6S1/2, 5D3/2 and 5D5/2). Measurements were performed on single 138Ba+ ions in a linear Paul trap with a frequency-doubled mode-locked Ti:Sapphire laser resonant with the 6S1/2->6P3/2 transition at 455 nm by detection of electron shelving into the dark 5D5/2 state. By driving a pi Rabi rotation with a single femtosecond pulse, a absolute measurement of the branching ratio to 5D5/2 state was performed. Combined with a measurement of the relative decay rates into 5D3/2 and 5D5/2 states performed with long trains of highly attenuated 455 nm pulses, it allowed the extraction of the absolute ratios of the other two decays. Relative strengths normalized to unity are found to be 0.756+/-0.046, 0.0290+/-0.0015 and 0.215+/-0.0064 for 6S1/2, 5D3/2 and 5D5/2 respectively. This approximately constitutes a threefold improvement over the best previous measurements and is a sufficient level of precision to compare to calculated values for dipole matrix elements.