arXiv subjects

Michael Brownnutt

Publications and source records attributed to Michael Brownnutt.

7 recordsLinked to original sources

arXiv2015

Electric-Field Noise above a Thin Dielectric Layer on Metal Electrodes

The electric-field noise above a layered structure composed of a planar metal electrode covered by a thin dielectric is evaluated and it is found that the dielectric film considerably increases the noise level, in proportion to its thickness. Importantly, even a thin (mono) layer of a low-loss dielectric can enhance the noise level by several orders of magnitude compared to the noise above a bare metal. Close to this layered surface, the power spectral density of the electric field varies with the inverse fourth power of the distance to the surface, rather than with the inverse square, as it would above a bare metal surface. Furthermore, compared to a clean metal, where the noise spectrum does not vary with frequency (in the radio-wave and microwave bands), the dielectric layer can generate electric-field noise which scales in inverse proportion to the frequency. For various realistic scenarios, the noise levels predicted from this model are comparable to those observed in trapped-ion experiments. Thus, these findings are of particular importance for the understanding and mitigation of unwanted heating and decoherence in miniaturized ion traps.

cond-mat.mtrl-sci↗

arXiv2015

Operation of a planar-electrode ion-trap array with adjustable RF electrodes

One path to realizing systems of trapped atomic ions suitable for large-scale quantum computing and simulation is to create a two-dimensional array of ion traps. Interactions between nearest-neighbouring ions could then be turned on and off by tuning the ions' relative positions and frequencies. We demonstrate and characterize the operation of a planar-electrode ion-trap array. Driving the trap with a network of phase-locked radio-frequency (RF) resonators which provide independently variable voltage amplitudes we vary the position and motional frequency of a 40Ca+ ion in two dimensions within the trap array. With suitable miniaturization of the trap structure, this provides a viable architecture for large-scale quantum simulations.

quant-ph↗

arXiv2015

Cryogenic silicon surface ion trap

Trapped ions are pre-eminent candidates for building quantum information processors and quantum simulators. They have been used to demonstrate quantum gates and algorithms, quantum error correction, and basic quantum simulations. However, to realise the full potential of such systems and make scalable trapped-ion quantum computing a reality, there exist a number of practical problems which must be solved. These include tackling the observed high ion-heating rates and creating scalable trap structures which can be simply and reliably produced. Here, we report on cryogenically operated silicon ion traps which can be rapidly and easily fabricated using standard semiconductor technologies. Single $^{40}$Ca$^+$ ions have been trapped and used to characterize the trap operation. Long ion lifetimes were observed with the traps exhibiting heating rates as low as $\dot{\bar{n}}=$ 0.33 phonons/s at an ion-electrode distance of 230 $μ$m. These results open many new avenues to arrays of micro-fabricated ion traps.

quant-ph↗

arXiv2011

Two-Dimensional Arrays of RF Ion Traps with Addressable Interactions

We describe the advantages of 2-dimensional, addressable arrays of spherical Paul traps. They would provide for the ability to address and tailor the interaction strengths of trapped objects in 2D and could establish a valuable new tool for quantum information processing. Simulations of trapping ions are compared to first tests using printed circuit board trap arrays loaded with dust particles. Pair-wise interactions in the array are addressed by means of an adjustable radio-frequency (RF) electrode shared between trapping sites. By attenuating this RF electrode potential, neighboring pairs of trapped objects have their interaction strength increase and are moved closer to one another. In the limit of the adjustable electrode being held at RF ground, the two formerly spherical traps are merged into one linear Paul trap.

quant-ph↗

arXiv2011

Spatially-resolved potential measurement with ion crystals

We present a method to measure potentials over an extended region using one-dimensional ion crystals in a radio frequency (RF) ion trap. The equilibrium spacings of the ions within the crystal allow the determination of the external forces acting at each point. From this the overall potential, and also potentials due to specific trap features, are calculated. The method can be used to probe potentials near proximal objects in real time, and can be generalized to higher dimensions.

quant-ph↗

arXiv2010

Trapped-ion antennae for the transmission of quantum information

More than one hundred years ago Heinrich Hertz succeeded in transmitting signals over a few meters to a receiving antenna using an electromagnetic oscillator and thus proving the electromagnetic theory developed by James C. Maxwell[1]. Since then, technology has developed, and today a variety of oscillators is available at the quantum mechanical level. For quantized electromagnetic oscillations atoms in cavities can be used to couple electric fields[2, 3]. For mechanical oscillators realized, for example, with cantilevers[4, 5] or vibrational modes of trapped atoms[6] or ions[7, 8], a quantum mechanical link between two such oscillators has, to date, been demonstrated in very few cases and has only been achieved in indirect ways. Examples of this include the mechanical transport of atoms carrying the quantum information[9] or the use of spontaneously emitted photons[10]. In this work, direct coupling between the motional dipoles of separately trapped ions is achieved over a distance of 54 μm, using the dipole-dipole interaction as a quantum-mechanical transmission line[11]. This interaction is small between single trapped ions, but the coupling is amplified by using additional trapped ions as antennae. With three ions in each well the interaction is increased by a factor of seven as compared to the singleion case. This enhancement facilitates bridging of larger distances and relaxes the constraints on the miniaturization of trap electrodes. This represents a new building block for quantum computation and also offers new opportunities to couple quantum systems of different natures.

quant-ph↗

arXiv2010

Trapped-ion probing of light-induced charging effects on dielectrics

We use a string of confined $^{40}$Ca$^+$ ions to measure perturbations to a trapping potential which are caused by light-induced charging of an anti-reflection coated window and of insulating patches on the ion-trap electrodes. The electric fields induced at the ions' position are characterised as a function of distance to the dielectric, and as a function of the incident optical power and wavelength. The measurement of the ion-string position is sensitive to as few as $40$ elementary charges per $\sqrt{\mathrm{Hz}}$ on the dielectric at distances of order millimetres, and perturbations are observed for illumination with light of wavelengths as long as 729\,nm. This has important implications for the future of miniaturised ion-trap experiments, notably with regards to the choice of electrode material, and the optics that must be integrated in the vicinity of the ion. The method presented can be readily applied to the investigation of charging effects beyond the context of ion trap experiments.

quant-ph↗