Quantum memory development and new slow light applications in rare-earth-ion-doped crystals
(2018)- Abstract
- When doped into solid state transparent crystals, rare-earth ions can have optically excited states with milliseconds coherence time and up to six hours coherence time for hyperfine levels after being cooled down to liquid helium temperature. This long coherence property makes them unique as solid state material and attractive for quantum information applications.
The rare-earth ions have narrow homogeneous linewidths on the order of ~ kHz. When doped into a crystal, the lattice structure is slightly distorted due to the size mismatch between the dopant and the host ions, resulting in slight differences in the local crystal fields at the dopant sites. Therefore, the resonance frequencies of the rare-earth ions are shifted... (More) - When doped into solid state transparent crystals, rare-earth ions can have optically excited states with milliseconds coherence time and up to six hours coherence time for hyperfine levels after being cooled down to liquid helium temperature. This long coherence property makes them unique as solid state material and attractive for quantum information applications.
The rare-earth ions have narrow homogeneous linewidths on the order of ~ kHz. When doped into a crystal, the lattice structure is slightly distorted due to the size mismatch between the dopant and the host ions, resulting in slight differences in the local crystal fields at the dopant sites. Therefore, the resonance frequencies of the rare-earth ions are shifted relatively, resulting in an inhomogeneously broadened absorption profile, typically on the order of a few GHz. This provides the possibility of addressing each group of ions individually and engineering the absorption profile for different purposes by optical pumping using a narrow linewidth laser, and makes rare-earth-ion-doped crystals suitable for ensemble based quantum memories.
Quantum memories are vital components for developing longdistance quantum communication. Part of this thesis project focused on making quantum memories with high efficiency and long storage time, especially using materials with low optical depth. To achieve this goal, a low finesse, unsymmetrical cavity was employed and experiments were carried out at (or close to) the impedance matched condition. Atomic frequency comb (AFC) protocol proposed for such an inhomogeneously broadened system was used to store coherent light for a certain time. 56% overall efficiency was achieved, and the main limiting factor for reaching even higher efficiency was the inefficient coupling between incoming light and the cavity mode. Other possible loss mechanisms were analyzed as well.
Long-time, on-demand, quantum memory experiments were conducted with the help of two efficient radio-frequency rephasing pulses. Storage time was extended from microseconds to milliseconds after compensating (most of) the residual earth magnetic field in the lab. The opportunities and challenges of combing the cavity assistant quantum memory and the long time, on demand quantum memory were analyzed and possible solutions were proposed.
Another part of the thesis project involves slow light-based applications in rare-earth-ion-doped crystals. The strong slow light effect at the presence a spectral hole is due to the fact that the light interacts with the absorbing ions outside the spectral hole off-resonantly, and most of the light energy is stored inside the ions as a polarization. For example, with a group velocity of 300 km/s, 99.9% of the pulse energy is stored in the ions when the pulse propagates inside the crystal. The slower the light propagates, the more energy is stored inside the medium. Based on this, a frequency shifter that is capable of shifting the light frequency of ± 4 MHz was demonstrated, and frequency shift up to GHz was proposed. Group velocity control by a factor of 20 and pulse compression in time by a factor of 2 were also demonstrated. The frequency shift and group velocity of the light are solely controlled by the external electric field, which makes them ideal for weak light situation. The unique property of such a frequency shifter and group velocity controller is that they could be made to accept light from an arbitrary incoming angle and polarization, for example, scattered light.
(Less)
Please use this url to cite or link to this publication:
https://lup.lub.lu.se/record/a16f47ae-8cef-45d4-95d8-db4e7c72dcd3
- author
- Li, Qian LU
- supervisor
- opponent
-
- Dr Chanelière, Thierry, Laboratoire Aimé Cotton - CNRS, Campus d’Orsay, France
- organization
- publishing date
- 2018
- type
- Thesis
- publication status
- published
- subject
- keywords
- Quantum memories, Slow light, Rare-earth-ion-doped crystals, Light-Matter Interaction, Fysicumarkivet A:2018:Li
- pages
- 173 pages
- publisher
- Atomic Physics, Department of Physics, Lund University
- defense location
- Lecture hall Rydbergsalen, Fysicum, Professorsgatan 1, Lund University, Faculty of Engineering LTH.
- defense date
- 2018-04-20 09:15:00
- ISBN
- 978-91-7753-616-1
- 978-91-7753-617-8
- language
- English
- LU publication?
- yes
- id
- a16f47ae-8cef-45d4-95d8-db4e7c72dcd3
- date added to LUP
- 2018-03-26 13:58:33
- date last changed
- 2019-05-13 15:55:39
@phdthesis{a16f47ae-8cef-45d4-95d8-db4e7c72dcd3,
abstract = {{When doped into solid state transparent crystals, rare-earth ions can have optically excited states with milliseconds coherence time and up to six hours coherence time for hyperfine levels after being cooled down to liquid helium temperature. This long coherence property makes them unique as solid state material and attractive for quantum information applications.<br/><br/>The rare-earth ions have narrow homogeneous linewidths on the order of ~ kHz. When doped into a crystal, the lattice structure is slightly distorted due to the size mismatch between the dopant and the host ions, resulting in slight differences in the local crystal fields at the dopant sites. Therefore, the resonance frequencies of the rare-earth ions are shifted relatively, resulting in an inhomogeneously broadened absorption profile, typically on the order of a few GHz. This provides the possibility of addressing each group of ions individually and engineering the absorption profile for different purposes by optical pumping using a narrow linewidth laser, and makes rare-earth-ion-doped crystals suitable for ensemble based quantum memories.<br/><br/>Quantum memories are vital components for developing longdistance quantum communication. Part of this thesis project focused on making quantum memories with high efficiency and long storage time, especially using materials with low optical depth. To achieve this goal, a low finesse, unsymmetrical cavity was employed and experiments were carried out at (or close to) the impedance matched condition. Atomic frequency comb (AFC) protocol proposed for such an inhomogeneously broadened system was used to store coherent light for a certain time. 56% overall efficiency was achieved, and the main limiting factor for reaching even higher efficiency was the inefficient coupling between incoming light and the cavity mode. Other possible loss mechanisms were analyzed as well.<br/><br/>Long-time, on-demand, quantum memory experiments were conducted with the help of two efficient radio-frequency rephasing pulses. Storage time was extended from microseconds to milliseconds after compensating (most of) the residual earth magnetic field in the lab. The opportunities and challenges of combing the cavity assistant quantum memory and the long time, on demand quantum memory were analyzed and possible solutions were proposed. <br/><br/>Another part of the thesis project involves slow light-based applications in rare-earth-ion-doped crystals. The strong slow light effect at the presence a spectral hole is due to the fact that the light interacts with the absorbing ions outside the spectral hole off-resonantly, and most of the light energy is stored inside the ions as a polarization. For example, with a group velocity of 300 km/s, 99.9% of the pulse energy is stored in the ions when the pulse propagates inside the crystal. The slower the light propagates, the more energy is stored inside the medium. Based on this, a frequency shifter that is capable of shifting the light frequency of ± 4 MHz was demonstrated, and frequency shift up to GHz was proposed. Group velocity control by a factor of 20 and pulse compression in time by a factor of 2 were also demonstrated. The frequency shift and group velocity of the light are solely controlled by the external electric field, which makes them ideal for weak light situation. The unique property of such a frequency shifter and group velocity controller is that they could be made to accept light from an arbitrary incoming angle and polarization, for example, scattered light.<br/>}},
author = {{Li, Qian}},
isbn = {{978-91-7753-616-1}},
keywords = {{Quantum memories; Slow light; Rare-earth-ion-doped crystals; Light-Matter Interaction; Fysicumarkivet A:2018:Li}},
language = {{eng}},
publisher = {{Atomic Physics, Department of Physics, Lund University}},
school = {{Lund University}},
title = {{Quantum memory development and new slow light applications in rare-earth-ion-doped crystals}},
url = {{https://lup.lub.lu.se/search/files/40458703/Qian_PhDThesie.pdf}},
year = {{2018}},
}