Rancic, Milos
Description
This thesis investigates the potential of Er:YSO and Er:Si for
quantum communication and computation applications. Erbium
uniquely possess optical transitions in the 1.5 um region, making
it suitable for both fibre telecommunication and silicon
photonics.
The properties of the ${I}_{15/2}\leftrightarrow{I}_{13/2}$
optical transition in Er:YSO have already been extensively
studied. Over two decades ago, improvements in $Er^{3+}$
dephasing time at 1.5 um...[Show more] were achieved by applying a 5T field
along the D1 axis. More recently, a record 4.4 ms coherence time
on the same optical transition was achieved using a 7T field.
These investigations, among others, illustrate that large Er
electron spins become thermally polarised with sufficient
magnetic field. However, no long lived and coherent spin
transitions associated with the Er ions had previously been
identified, and such transitions are necessary for on-demand
quantum state storage.
To address this requirement, the optical and hyperfine transition
properties of 167-Er:YSO were investigated in large magnetic
fields. In a field of 7T, spectral hole lifetimes of 1 minute and
hyperfine population lifetimes of 12 minutes were observed. These
measurements illustrate the effect of spin-lattice relaxation in
this system, and how it can be mitigated.
Efficient spin-polarisation of the entire 167-Er hyperfine
ensemble is also demonstrated. This is the first such
demonstration in rare earth systems, and a key requirement for
broadband optical storage. Moreover, a 1.3 second coherence time
was recorded for an 167-Er:YSO hyperfine transition at 7T and 1.4
K. This is an improvement of several orders-of-magnitude over
previous coherence measurements on spin-transitions in Er doped
solids. This is also sufficient for maximal entanglement rates in
quantum repeater networks that span distances of 1000 km or
greater.
With an optical transition at 1.5 um, Er is also an ideal
candidate to connect silicon based quantum computers to the
future quantum Internet. In particular, single Er:Si ions could
be used to develop an optical-spin bus between P:Si qubits and
fibre based quantum networks.
Presented here is the first spectroscopic investigation of single
Er:Si ions. This required a novel opto-electronic approach to
single ion detection, where the Er ions are implanted into a
nanometre scale fin-shaped Field Effect Transistor. With this
approach it was possible to develop high resolution optical
spectra, where both the electronic and hyperfine levels of
individual Er ions were resolved.
Long optical and spin coherence times are also important
requirements for an optical-spin bus. To address the first
requirement, an investigation of the optical lineshape was
undertaken. Here it was determined that sources of Stark noise
external to the transistor channel contribute a significant
amount to optical homogeneous linewidth. However, the dominant
noise contribution was determined to be short-range (from within
the 30 nm wide channel) and the total homogeneous linewidth was
measured to be 50 MHz.
The site structure of an individual Er:Si ion was then analysed,
using magnetic field rotation patterns and optical transitions
between multiple crystal field levels. This site was determined
to have approximately axial ($C_{3}$) symmetry. The purpose of
this study was to determine a magnetic field regime in which the
Er electrons spin can be polarised, which is necessary for
realising of long hyperfine lifetimes and coherence times.
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