Addressing Single Yb+ Ions (English shop)

A new scheme for quantum computing in linear ion traps

Preview

Table of Contents, Datei (44 KB)
Extract, Datei (140 KB)

This work reports on the individual addressing of single ytterbium ions confined in a linear Paul
trap. The addressing procedure is one step in a new scheme for quantum computing in linear
ion traps. This thesis presents the first experimental implementation of this scheme. 172Yb+
ions are laser cooled to the Doppler limit and form a linear ion crystal. Such a string of ions
can be used for quantum computing, where each ion represents a qubit. A quantum algorithm
necessarily contains a sequence of coherent manipulations of the state of the ions. A prerequisite
for these manipulations is the ability to address the qubits independently. The degeneracy of the
different qubits is lifted by applying a static magnetic field gradient. The spatially inhomogeneous
magnetic field induces a Zeeman-splitting that is dependent on the position of the ions. The ions
can thus be addressed by changing the frequency of the interacting electro-magnetic field.
The four-level Doppler-cooling cycle involves two laser transitions near 369 nm, driving the
ground-state transition from the 2S1/2 (4f146s) to the 2P1/2 (4f146p) level, and close to 935 nm,
coupling the 2D3/2 (4f145d) level to the 2[3/2]1/2 (4f135d6s) level. The D3/2 state has four Zeeman-
sublevels that are used here to demonstrate individual addressing of single ions. A radio-frequency
optical double-resonance spectroscopy was set up to probe the state of the four sub-levels of
the D3/2 level. The levels are coherently coupled by rf-radiation at the Larmor-frequency of
the Zeeman-splitting. The spectroscopy itself was investigated in detail, as it forms the basis
for the actual addressing measurements. These were subsequently performed successfully and
demonstrate the feasibility of the gradient scheme. Measurements for the addressing of two,
three, five and sixteen ions are presented. The maximal magnetic field gradient attained was
0.51(2) T/m.
During the course of this thesis a linear trap was put to operation. This is the first time a
linear Paul trap has been employed to experiment with cold Yb-ion crystals. The rf-spectroscopy
allowed for the measurement of the gj factor of the D3/2 state. The measurement represents the
first experimental verification of a historical footnote [Fawcett & Wilson, 1991] pertaining to the
measurement of the gj value by Meggers in 1967, and confirms LS-coupling. As an important step
to simplify the trapping procedure itself photo-ionization – with many advantages over electron
impact ionization – of ytterbium atoms has been realized. This is the first time for ion trap
purposes that ytterbium ions have been produced by photo-ionization. Last but not least a new
design for the trap drives creating the trapping potential has been implemented that proved to
be experimentally robust with regard to amplitude and frequency stability.