76 research outputs found
Optical and structural properties of InGaAs self assembled quantum dots
Imperial Users onl
Yb ion trap experimental set-up and two-dimensional ion trap surface array design towards analogue quantum simulations
Ions trapped in Paul traps provide a system which has been shown to exhibit most of
the properties required to implement quantum information processing. In particular, a
two-dimensional array of ions has been shown to be a candidate for the implementation of quantum simulations. Microfabricated surface geometries provide a widely used technology
with which to create structures capable of trapping the required two-dimensional array of ions. To provide a system which can utilise the properties of trapped ions a greater understanding of the surface geometries which can trap ions in two-dimensional arrays would be advantageous, and allow quantum simulators to be fabricated and tested.
In this thesis I will present the design, set-up and implementation of an experimental
apparatus which can be used to trap ions in a variety of different traps. Particular focus will
be put on the ability to apply radio-frequency voltages to these traps via helical resonators
with high quality factors. A detailed design guide will be presented for the construction
and operation of such a device at a desired resonant frequency whilst maximising the
quality factor for a set of experimental constraints. Devices of this nature will provide
greater filtering of noise on the rf voltages used to create the electric field which traps
the ions which could lead to reduced heating in trapped ions. The ability to apply higher
voltages with these devices could also provide deeper traps, longer ion lifetimes and more
efficient cooling of trapped ions.
In order to efficiently cool trapped ions certain transitions must be known to a required
accuracy. In this thesis the 2S1/2 → 2P1/2 Doppler cooling and 2D3/2 → 2D[3/2]1/2 repumping transition wavelengths are presented with a greater accuracy then previous work. These transitions are given for the 170, 171, 172, 174 and 176 isotopes of Yb+.
Two-dimensional arrays of ions trapped above a microfabricated surface geometry
provide a technology which could enable quantum simulations to be performed allowing
solutions to problems currently unobtainable with classical simulation. However, the spin-spin interactions used in the simulations between neighbouring ions are required to occur on a faster time-scale than any decoherence in the system. The time-scales of both the ion-ion interactions and decoherence are determined by the properties of the electric field formed by the surface geometry. This thesis will show how geometry variables can be used to optimise the ratio between the decoherence time and the interaction time whilst simultaneously maximising the homogeneity of the array properties. In particular, it will be shown how the edges of the geometry can be varied to provide the maximum homogeneity in the array and how the radii and separation of polygons comprising the surface geometry vary as a function of array size for optimised arrays. Estimates of the power dissipation in these geometries will be given based on a simple microfabrication
Optimisation of two-dimensional ion trap arrays for quantum simulation
The optimisation of two-dimensional (2D) lattice ion trap geometries for
trapped ion quantum simulation is investigated. The geometry is optimised for
the highest ratio of ion-ion interaction rate to decoherence rate. To calculate
the electric field of such array geometries a numerical simulation based on a
"Biot-Savart like law" method is used. In this article we will focus on square,
hexagonal and centre rectangular lattices for optimisation. A method for
maximising the homogeneity of trapping site properties over an array is
presented for arrays of a range of sizes. We show how both the polygon radii
and separations scale to optimise the ratio between the interaction and
decoherence rate. The optimal polygon radius and separation for a 2D lattice is
found to be a function of the ratio between rf voltage and drive frequency
applied to the array. We then provide a case study for 171Yb+ ions to show how
a two-dimensional quantum simulator array could be designed
Low noise quantum frequency conversion of photons from a trapped barium ion to the telecom O-band
Trapped ions are one of the leading candidates for scalable and long-distance
quantum networks because of their long qubit coherence time, high fidelity
single- and two-qubit gates, and their ability to generate photons entangled
with the qubit state of the ion. One method for creating ion-photon
entanglement is to exploit optically transitions from the P_(1/2) to S_(1/2)
levels, which naturally emit spin-photon entangled states. But these optical
transitions typically lie in the ultra-violet and visible wavelength regimes.
These wavelengths exhibit significant fiber-optic propagation loss, thereby
limiting the transfer of quantum information to tens of meters. Quantum
frequency conversion is essential to convert these photons to telecom
wavelengths so that they can propagate over long distances in fiber-based
networks, as well as for compatibility with the vast number of telecom-based
opto-electronic components. Here, we generate O-band telecom photons via a low
noise quantum frequency conversion scheme from photons emitted from the P_(1/2)
to S_(1/2) dipole transition of a trapped barium ion. We use a two-stage
quantum frequency conversion scheme to achieve a frequency shift of 375.4 THz
between the input visible photon and the output telecom photon achieving a
conversion efficiency of 11%. We attain a signal-to-background ratio of over
100 for the converted O-band telecom photon with background noise less than 15
counts/sec. These results are an important step toward achieving trapped ion
quantum networks over long distances for distributed quantum computing and
quantum communication
Versatile ytterbium ion trap experiment for operation of scalable ion-trap chips with motional heating and transition-frequency measurements
We present the design and operation of an ytterbium ion trap experiment with a setup offering versatile optical access and 90 electrical interconnects that can host advanced surface and multilayer ion trap chips mounted on chip carriers. We operate a macroscopic ion trap compatible with this chip carrier design and characterize its performance, demonstrating secular frequencies >1 MHz, and trap and cool nearly all of the stable isotopes, including 171Yb+ ions, as well as ion crystals. For this particular trap we measure the motional heating rate 〈ṅ〉 and observe an 〈ṅ〉∝1/ω2 behavior for different secular frequencies ω. We also determine a spectral noise density SE(1 MHz)=3.6(9)×10-11 V2 m-2 Hz-1 at an ion electrode spacing of 310(10) μm. We describe the experimental setup for trapping and cooling Yb+ ions and provide frequency measurements of the 2S1/2↔2P1/2 and 2D3/2↔3D[3/2]1/2 transitions for the stable 170Yb+, 171Yb+, 172Yb+, 174Yb+, and 176Yb+ isotopes which are more precise than previously published work
Effects of residual stress in creep crack growth analysis of cold bent tubes under internal pressure
- …