Yao, Qi
(2024)
Ballistic Transport and Persistent Circulation of Exciton-Polariton Condensates.
Doctoral Dissertation, University of Pittsburgh.
(Unpublished)
Abstract
Bose-Einstein condensation (BEC) is a quantum macroscopic phenomenon and is closely related to superfluidity and superconductivity. Exciton-polaritons (polaritons) are a kind of quasi-particles, which are superpositions of excitons and photons in semiconductor microcavities. They have low effective mass due to their photon part and interact with each other due to their exciton part. With these properties, polariton BEC can be created at helium temperature (~10K).
This thesis mainly focuses on creating persistent circulation out of polariton condensates in ring structures. In the first experiment, polariton condensate was injected at one point in an etched quasi-1D ring. Rather than observing the circulation, the condensates transported ballistically, and a clear precession of the polarization was seen, which arises from an effective spin-orbit coupling term in the Hamiltonian. In the second experiment, we created a non-circulating condensate by using an optical trap and initiated the circulation in either direction on demand by a short laser pulse. The circulation direction only depends on the short pulse location relative to the intensity distribution of the non-circulating ring and the circulation persisted for at least 13ns, which is much longer than the polariton lifetime (~200ps) or the pulse duration (2ps). This experiment demonstrates the canonical effect of superfluidity and has potential applications for phase memory or optical qubits.
In addition, I did research on polariton condensates in other geometries. One is experimental research, where I observed polariton drag effect in wire structures. In this experiment, the condensate momentum was modified by a direct electrical current. This is equivalent to electrically steering light momentum. The other is numerical simulation of the etching-induced strain. Our goal was to optimize the Y-shape devices because the condensate from the lower arm wouldn't travel to the upper arms. The simulation was first applied to a square-shape pillar, which matched the experiments pretty well. The simulation indicates that the potential at the junction of the Y-shape devices is flat so strain is not the reason that prevented the condensate flow. More research needs to be done to have the best design.
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Details
| Item Type: |
University of Pittsburgh ETD
|
| Status: |
Unpublished |
| Creators/Authors: |
|
| ETD Committee: |
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| Date: |
27 August 2024 |
| Date Type: |
Publication |
| Defense Date: |
10 April 2024 |
| Approval Date: |
27 August 2024 |
| Submission Date: |
16 June 2024 |
| Access Restriction: |
No restriction; Release the ETD for access worldwide immediately. |
| Number of Pages: |
156 |
| Institution: |
University of Pittsburgh |
| Schools and Programs: |
Dietrich School of Arts and Sciences > Physics |
| Degree: |
PhD - Doctor of Philosophy |
| Thesis Type: |
Doctoral Dissertation |
| Refereed: |
Yes |
| Uncontrolled Keywords: |
Microcavity Polaritons, Bose-Einstein Condensation, Ring Trap, Superfluidity, Persistent Circulation, Quantized Flow. |
| Date Deposited: |
27 Aug 2024 14:15 |
| Last Modified: |
27 Aug 2024 14:15 |
| URI: |
http://d-scholarship.pitt.edu/id/eprint/46514 |
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