Person: Barthel, C
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Barthel
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Barthel, C
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Publication Relaxation and readout visibility of a singlet-triplet qubit in an Overhauser field gradient(American Physical Society (APS), 2012) Barthel, C; Medford, James Redding; Bluhm, H.; Yacoby, Amir; Marcus, C; Hanson, M. P.; Gossard, A. C.Using single-shot charge detection in a GaAs double quantum dot, we investigate spin relaxation time (T1) and readout visibility of a two-electron singlet-triplet qubit following single-electron dynamic nuclear polarization (DNP). For magnetic fields up to 2 T, the DNP cycle is in all cases found to increase Overhauser field gradients, which in turn decrease T1 and, consequently, reduce readout visibility. This effect was previously attributed to a suppression of singlet-triplet dephasing under a similar DNP cycle. A model describing relaxation after singlet-triplet mixing agrees well with experiment. Effects of pulse bandwidth on visibility are also investigated.Publication Hyperfine-Mediated Gate-Driven Electron Spin Resonance(American Physical Society (APS), 2007) Laird, Elise; Barthel, C; Rashba, Emmanuel; Marcus, Carolyn; Hanson, Mark Jonathan; Gossard, A. C.An all-electrical spin resonance effect in a GaAs few-electron double quantum dot is investigated experimentally and theoretically. The magnetic field dependence and absence of associated Rabi oscillations are consistent with a novel hyperfine mechanism. The resonant frequency is sensitive to the instantaneous hyperfine effective field, and the effect can be used to detect and create sizable nuclear polarizations. A device incorporating a micromagnet exhibits a magnetic field difference between dots, allowing electrons in either dot to be addressed selectively.Publication A New Mechanism of Electric Dipole Spin Resonance: Hyperfine Coupling in Quantum Dots(Institute of Physics, 2009) Laird, Edward A.; Barthel, C; Rashba, Emmanuel; Marcus, C; Hanson, M. P.; Gossard, Arthur C.A recently discovered mechanism of electric dipole spin resonance, mediated by the hyperfine interaction, is investigated experimentally and theoretically. The effect is studied using a spin-selective transition in a GaAs double quantum dot. The resonant frequency is sensitive to the instantaneous hyperfine effective field, revealing a nuclear polarization created by driving the resonance. A device incorporating a micromagnet exhibits a magnetic field difference between dots, allowing electrons in either dot to be addressed selectively. An unexplained additional signal at half the resonant frequency is presented.Publication Fast Sensing of Double-Dot Charge Arrangement and Spin State with a Radio-Frequency Sensor Quantum Dot(American Physical Society, 2010) Barthel, C; Kjærgaard, M.; Medford, James Redding; Stopa, Michael P; Marcus, C; Hanson, M. P.; Gossard, Arthur C.Single-shot measurement of the charge arrangement and spin state of a double quantum dot are reported with measurement times down to 100 ns. Sensing uses radio-frequency reflectometry of a proximal quantum dot in the Coulomb blockade regime. The sensor quantum dot is up to 30 times more sensitive than a comparable quantum point-contact sensor and yields three times greater signal to noise in rf single-shot measurements. Numerical modeling is qualitatively consistent with experiment and shows that the improved sensitivity of the sensor quantum dot results from reduced lifetime broadening and screening.Publication Rapid Single-Shot Measurement of a Singlet-Triplet Qubit(American Physical Society, 2009) Barthel, C; Reilly, David; Marcus, C; Hanson, M. P.; Gossard, ArthurWe report repeated single-shot measurements of the two-electron spin state in a GaAs double quantum dot. The readout allows measurement with a fidelity above 90% with a ∼7 μs cycle time. Hyperfine-induced precession between singlet and triplet states of the two-electron system are directly observed, as nuclear Overhauser fields are quasistatic on the time scale of the measurement cycle. Repeated measurements on millisecond to second time scales reveal the evolution of the nuclear environment.