Micro-cavity optimization for single ion fluorescence detection
(2025)- Abstract
- This thesis describes the work done on two open access microcavities that aims at detecting single rare-earth ions for quantum information applications. The initial microcavity faced mechanical instability due to its geometry, which limited robust design possibilities due to the 25 mm diameter space of the helium bath cryostat. A Purcell enhancement of 2.2 was realized for nanoparticles at 2.1 K, compared to an estimated enhancement of 18. The observed decrease in Purcell enhancement is attributed to the root mean square (rms) cavity length fluctuations, which resulted in a time-averaged Purcell effect. A cavity length jitter of 4 linewidths has been observed to cause significant fluctuations in the detected fluorescence signal, which... (More)
- This thesis describes the work done on two open access microcavities that aims at detecting single rare-earth ions for quantum information applications. The initial microcavity faced mechanical instability due to its geometry, which limited robust design possibilities due to the 25 mm diameter space of the helium bath cryostat. A Purcell enhancement of 2.2 was realized for nanoparticles at 2.1 K, compared to an estimated enhancement of 18. The observed decrease in Purcell enhancement is attributed to the root mean square (rms) cavity length fluctuations, which resulted in a time-averaged Purcell effect. A cavity length jitter of 4 linewidths has been observed to cause significant fluctuations in the detected fluorescence signal, which hinders the detection of single ions, particularly in scenarios with low Purcell enhancement. Consequently, approximately 7 ions affect the fluorescence measurements.
Nevertheless, our focus is on single ion detection, which is essential for quantum computer applications (see Chapter 8). In my thesis project, I focused on developing a new microcavity assembly to resolve the issues associated with the previous design. The mechanical design is detailed in Chapter 5, while Chapter 6 addresses the stability measurements. The objective of the new assembly is to attain high mechanical stability within a closed-cycle cryostat, providing sufficient space for a robust design and minimizing photon leakage from the stabilization beam to the fluorescence detection system. This integration enables the use of a continuous wave laser for stabilization, which contributes to reduced cavity length fluctuations during fluorescence collection and enhances the Purcell effect. To attain a significant degree of mechanical stability while minimizing error photons, higher-order modes, particularly those with odd indices, are employed as a stabilization beam. This approach is effective because odd-indexed higher-order modes exhibit minimal overlap with the single-mode fiber used for sample probing and fluorescence collection. Chapter 4 analyzes suppression in coupling efficiency due to odd-indexed higher-order modes, ranging from 10 to 102, depending on excited mode and cavity length. A challenge associated with higher-order modes is the diffraction loss resulting from the finite diameter of the fiber mirror, which is dependent on the mode order. This aspect is essential when employing higher-order modes for stabilization, as the cavity length stabilization depends on the slope of the fringe side used for stabilization. A cavity finesse of 1600 was measured for the TEM00 and TEM10 locking beams. In contrast, the finesse measurements for other higher-order modes showed a finesse of 800 for TEM30 and 400 for TEM50, attributed to diffraction losses. The associated root mean square (rms) cavity length jitters ranged from 1.5 pm to 2.5 pm measured at room temperature and using side-of-fringe locking. A threefold improvement in stability has been achieved through the implementation of a tilt locking scheme, which can be attributed to the observed steeper slope. At a temperature of 10 K, a cavity length jitter of 15 pm has been measured using side-of-fringe locking. This increase in length fluctuation is primarily due to noise from the closed cycle cryostat, predominantly arising from the vibration noise generated by the pulse tube cryocooler. For the measured length fluctuations an enhancement of an effective Purcell factor of 15 is anticipated with the second generation microcavity assembly. This enhancement allows for excitation power levels below 100 nW, significantly reducing power broadening from 36 MHz to under 1 MHz. Since this is factor is less than the 7 ions we can currently resolve, we can expect that a single rare-earth ion should be resolvable with the current setup.
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Please use this url to cite or link to this publication:
https://lup.lub.lu.se/record/9e43e148-8e78-4d76-aa19-98bf09386333
- author
- Abdelatief, Abdullah LU
- supervisor
-
- Andreas Walther LU
- Adam Kinos LU
- opponent
-
- Assoc. Prof. Julsgaard, Brian, Aarhus University, Denmark.
- organization
- publishing date
- 2025-01-17
- type
- Thesis
- publication status
- published
- subject
- pages
- 134 pages
- publisher
- Atomic Physics, Department of Physics, Lund University
- defense location
- Lecture Hall Rydbergsalen, Department of Physics, Professorsgatan 1, Faculty of Engineering LTH, Lund University, Lund.
- defense date
- 2025-02-21 09:15:00
- ISBN
- 978-91-8104-367-9
- 978-91-8104-366-2
- language
- English
- LU publication?
- yes
- id
- 9e43e148-8e78-4d76-aa19-98bf09386333
- date added to LUP
- 2025-01-17 22:40:49
- date last changed
- 2025-04-04 14:08:48
@phdthesis{9e43e148-8e78-4d76-aa19-98bf09386333,
abstract = {{This thesis describes the work done on two open access microcavities that aims at detecting single rare-earth ions for quantum information applications. The initial microcavity faced mechanical instability due to its geometry, which limited robust design possibilities due to the 25 mm diameter space of the helium bath cryostat. A Purcell enhancement of 2.2 was realized for nanoparticles at 2.1 K, compared to an estimated enhancement of 18. The observed decrease in Purcell enhancement is attributed to the root mean square (rms) cavity length fluctuations, which resulted in a time-averaged Purcell effect. A cavity length jitter of 4 linewidths has been observed to cause significant fluctuations in the detected fluorescence signal, which hinders the detection of single ions, particularly in scenarios with low Purcell enhancement. Consequently, approximately 7 ions affect the fluorescence measurements.<br/>Nevertheless, our focus is on single ion detection, which is essential for quantum computer applications (see Chapter 8). In my thesis project, I focused on developing a new microcavity assembly to resolve the issues associated with the previous design. The mechanical design is detailed in Chapter 5, while Chapter 6 addresses the stability measurements. The objective of the new assembly is to attain high mechanical stability within a closed-cycle cryostat, providing sufficient space for a robust design and minimizing photon leakage from the stabilization beam to the fluorescence detection system. This integration enables the use of a continuous wave laser for stabilization, which contributes to reduced cavity length fluctuations during fluorescence collection and enhances the Purcell effect. To attain a significant degree of mechanical stability while minimizing error photons, higher-order modes, particularly those with odd indices, are employed as a stabilization beam. This approach is effective because odd-indexed higher-order modes exhibit minimal overlap with the single-mode fiber used for sample probing and fluorescence collection. Chapter 4 analyzes suppression in coupling efficiency due to odd-indexed higher-order modes, ranging from 10 to 102, depending on excited mode and cavity length. A challenge associated with higher-order modes is the diffraction loss resulting from the finite diameter of the fiber mirror, which is dependent on the mode order. This aspect is essential when employing higher-order modes for stabilization, as the cavity length stabilization depends on the slope of the fringe side used for stabilization. A cavity finesse of 1600 was measured for the TEM00 and TEM10 locking beams. In contrast, the finesse measurements for other higher-order modes showed a finesse of 800 for TEM30 and 400 for TEM50, attributed to diffraction losses. The associated root mean square (rms) cavity length jitters ranged from 1.5 pm to 2.5 pm measured at room temperature and using side-of-fringe locking. A threefold improvement in stability has been achieved through the implementation of a tilt locking scheme, which can be attributed to the observed steeper slope. At a temperature of 10 K, a cavity length jitter of 15 pm has been measured using side-of-fringe locking. This increase in length fluctuation is primarily due to noise from the closed cycle cryostat, predominantly arising from the vibration noise generated by the pulse tube cryocooler. For the measured length fluctuations an enhancement of an effective Purcell factor of 15 is anticipated with the second generation microcavity assembly. This enhancement allows for excitation power levels below 100 nW, significantly reducing power broadening from 36 MHz to under 1 MHz. Since this is factor is less than the 7 ions we can currently resolve, we can expect that a single rare-earth ion should be resolvable with the current setup.<br/>}},
author = {{Abdelatief, Abdullah}},
isbn = {{978-91-8104-367-9}},
language = {{eng}},
month = {{01}},
publisher = {{Atomic Physics, Department of Physics, Lund University}},
school = {{Lund University}},
title = {{Micro-cavity optimization for single ion fluorescence detection}},
url = {{https://lup.lub.lu.se/search/files/206188396/e-nailing_ex_abdullah.pdf}},
year = {{2025}},
}