Electron spin resonance of molecular magnets for quantum information processing
<p>Quantum information processors have been shown theoretically to outperform their classical counterparts at certain tasks. They comprise two level systems, which can exist in an arbitrary superposition of states: qubits. A strong candidate qubit is the molecular nanomagnet (MNM). In this the...
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| Natura: | Tesi |
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2015
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| _version_ | 1826305510006063104 |
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| author | Kaminski, D |
| author2 | Ardavan, A |
| author_facet | Ardavan, A Kaminski, D |
| author_sort | Kaminski, D |
| collection | OXFORD |
| description | <p>Quantum information processors have been shown theoretically to outperform their classical counterparts at certain tasks. They comprise two level systems, which can exist in an arbitrary superposition of states: qubits. A strong candidate qubit is the molecular nanomagnet (MNM). In this thesis, electron spin resonance is used to explore the potential of Cr7M based MNMs as elements of a quantum information processor.</p> <p>We explore the possibility and effect of replacing H atoms with D or a halogen atom in a S &equals; 1/2 Cr7Ni ring. Decoherence mechanisms in the resulting compounds are found to be dominated by structural effects. We conclude that halogenation does not seem to be a productive strategy for extension of coherence times in Cr7Ni based compounds.</p> <p>We examine an asymmetric dimer, in which a Cr7Ni ring is linked to a highly coherent nitrogen atom within a carbon cage. Measurement of phase memory time across a range of temperatures for the N spin, provides insight into the ring's spin dynamics. At high temperature, fluctuations on the ring are so rapid that the N spin appears magnetically disconnected; as they slow, we see a sharp rise in the decoherence rate of the N spin. At the lowest temperatures, a recovery of the decoherence rate reflects the onset of the ring’s coherent ground state.</p> <p>A group of symmetric Cr7Ni-Cr7Ni dimers is investigated. Through use of double electron-electron resonance, the strength of the ring-ring dipolar interaction, governing the two qubit gate time, is estimated for each. It is found that many exhibit the hierarchy of timescales required for implementation of a two qubit gate: a short single qubit manipulation time, intermediate two-qubit gate time and long phase coherence time. A possible scheme for the future implementation of a CNOT gate is presented.</p> <p>The final study explores rings of spin, S > 1/2. We present the first ever coherent measurements on a dilute oriented ensemble of the S &equals; 3/2 rings, Cr7Zn, performing nutations at various powers. In addition, we investigate the anisotropic Mn2+ (s &equals; 5/2, I &equals; 5/2) defect in ZnO. We develop the 'echo kill' method for identification of a three level subsystem whose transition frequencies both fall within the cavity bandwidth. Such a subsystem is then used to perform indirectly detected nutations between the upper two levels over a range of applied powers. Finally, a method for initialisation of the subsystem into a pseudopure state is presented and shown to enhance nutation amplitude.</p> |
| first_indexed | 2024-03-07T06:33:55Z |
| format | Thesis |
| id | oxford-uuid:f6f50d1d-dea8-48ce-973f-370a0173ba02 |
| institution | University of Oxford |
| last_indexed | 2024-03-07T06:33:55Z |
| publishDate | 2015 |
| record_format | dspace |
| spelling | oxford-uuid:f6f50d1d-dea8-48ce-973f-370a0173ba022022-03-27T12:39:01ZElectron spin resonance of molecular magnets for quantum information processingThesishttp://purl.org/coar/resource_type/c_db06uuid:f6f50d1d-dea8-48ce-973f-370a0173ba02ORA Deposit2015Kaminski, DArdavan, A<p>Quantum information processors have been shown theoretically to outperform their classical counterparts at certain tasks. They comprise two level systems, which can exist in an arbitrary superposition of states: qubits. A strong candidate qubit is the molecular nanomagnet (MNM). In this thesis, electron spin resonance is used to explore the potential of Cr7M based MNMs as elements of a quantum information processor.</p> <p>We explore the possibility and effect of replacing H atoms with D or a halogen atom in a S &equals; 1/2 Cr7Ni ring. Decoherence mechanisms in the resulting compounds are found to be dominated by structural effects. We conclude that halogenation does not seem to be a productive strategy for extension of coherence times in Cr7Ni based compounds.</p> <p>We examine an asymmetric dimer, in which a Cr7Ni ring is linked to a highly coherent nitrogen atom within a carbon cage. Measurement of phase memory time across a range of temperatures for the N spin, provides insight into the ring's spin dynamics. At high temperature, fluctuations on the ring are so rapid that the N spin appears magnetically disconnected; as they slow, we see a sharp rise in the decoherence rate of the N spin. At the lowest temperatures, a recovery of the decoherence rate reflects the onset of the ring’s coherent ground state.</p> <p>A group of symmetric Cr7Ni-Cr7Ni dimers is investigated. Through use of double electron-electron resonance, the strength of the ring-ring dipolar interaction, governing the two qubit gate time, is estimated for each. It is found that many exhibit the hierarchy of timescales required for implementation of a two qubit gate: a short single qubit manipulation time, intermediate two-qubit gate time and long phase coherence time. A possible scheme for the future implementation of a CNOT gate is presented.</p> <p>The final study explores rings of spin, S > 1/2. We present the first ever coherent measurements on a dilute oriented ensemble of the S &equals; 3/2 rings, Cr7Zn, performing nutations at various powers. In addition, we investigate the anisotropic Mn2+ (s &equals; 5/2, I &equals; 5/2) defect in ZnO. We develop the 'echo kill' method for identification of a three level subsystem whose transition frequencies both fall within the cavity bandwidth. Such a subsystem is then used to perform indirectly detected nutations between the upper two levels over a range of applied powers. Finally, a method for initialisation of the subsystem into a pseudopure state is presented and shown to enhance nutation amplitude.</p> |
| spellingShingle | Kaminski, D Electron spin resonance of molecular magnets for quantum information processing |
| title | Electron spin resonance of molecular magnets for quantum information processing |
| title_full | Electron spin resonance of molecular magnets for quantum information processing |
| title_fullStr | Electron spin resonance of molecular magnets for quantum information processing |
| title_full_unstemmed | Electron spin resonance of molecular magnets for quantum information processing |
| title_short | Electron spin resonance of molecular magnets for quantum information processing |
| title_sort | electron spin resonance of molecular magnets for quantum information processing |
| work_keys_str_mv | AT kaminskid electronspinresonanceofmolecularmagnetsforquantuminformationprocessing |