| 1. |
- Burnett, Jonathan, 1987, et al.
(författare)
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Decoherence benchmarking of superconducting qubits
- 2019
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Ingår i: npj Quantum Information. - : Springer Science and Business Media LLC. - 2056-6387. ; 5:1
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Tidskriftsartikel (refereegranskat)abstract
- We benchmark the decoherence of superconducting transmon qubits to examine the temporal stability of energy relaxation, dephasing, and qubit transition frequency. By collecting statistics during measurements spanning multiple days, we find the mean parameters (T) over bar (1) = 49 mu s and (T) over bar (2)* = 95 mu s; however, both of these quantities fluctuate, explaining the need for frequent re-calibration in qubit setups. Our main finding is that fluctuations in qubit relaxation are local to the qubit and are caused by instabilities of near-resonant two-level-systems (TLS). Through statistical analysis, we determine sub-millihertz switching rates of these TLS and observe the coherent coupling between an individual TLS and a transmon qubit. Finally, we find evidence that the qubit's frequency stability produces a 0.8 ms limit on the pure dephasing which we also observe. These findings raise the need for performing qubit metrology to examine the reproducibility of qubit parameters, where these fluctuations could affect qubit gate fidelity.
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| 2. |
- Cubaynes, T., et al.
(författare)
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Highly coherent spin states in carbon nanotubes coupled to cavity photons
- 2019
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Ingår i: npj Quantum Information. - : Springer Science and Business Media LLC. - 2056-6387. ; 5
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Tidskriftsartikel (refereegranskat)abstract
- Spins confined in quantum dots are considered as a promising platform for quantum information processing. While many advanced quantum operations have been demonstrated, experimental as well as theoretical efforts are now focusing on the development of scalable spin quantum bit architectures. One particularly promising method relies on the coupling of spin quantum bits to microwave cavity photons. This would enable the coupling of distant spins via the exchange of virtual photons for two qubit gate applications, which still remains to be demonstrated with spin qubits. Here, we use a circuit QED spin-photon interface to drive a single electronic spin in a carbon nanotube-based double quantum dot using cavity photons. The microwave spectroscopy allows us to identify an electrically controlled spin transition with a decoherence rate which can be tuned to be as low as 250 kHz. We show that this value is consistent with the expected hyperfine coupling in carbon nanotubes. These coherence properties, which can be attributed to the use of pristine carbon nanotubes stapled inside the cavity, should enable coherent spin-spin interaction via cavity photons and compare favorably to the ones recently demonstrated in Si-based circuit QED experiments. Our clean and controlled nano-assembly technique of carbon nanotubes in the cavity could be further improved by purified C-12 growth to get rid of the nuclear spins resulting in an even higher spin coherence.
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