Showing papers by "Jason R. Petta published in 2008"
TL;DR: A method of preparing the nuclear spin environment that suppresses the relevant component of nuclear spin fluctuations below its equilibrium value by a factor of ∼70 is reported, extending the inhomogeneous dephasing time for the two-electron spin state beyond 1 microsecond.
Abstract: Coherent spin states in semiconductor quantum dots offer promise as electrically controllable quantum bits (qubits) with scalable fabrication. For few-electron quantum dots made from gallium arsenide (GaAs), fluctuating nuclear spins in the host lattice are the dominant source of spin decoherence. We report a method of preparing the nuclear spin environment that suppresses the relevant component of nuclear spin fluctuations below its equilibrium value by a factor of approximately 70, extending the inhomogeneous dephasing time for the two-electron spin state beyond 1 microsecond. The nuclear state can be readily prepared by electrical gate manipulation and persists for more than 10 seconds.
190 citations
TL;DR: A self-limiting pulse sequence is developed that allows the steady-state nuclear polarization to be set using a gate voltage and the resulting Overhauser field approaches 80 mT, in agreement with a simple rate-equation model.
Abstract: We polarize nuclear spins in a GaAs double quantum dot by controlling two-electron spin states near the anticrossing of the singlet (S) and mS �� 1 triplet (T� ) using pulsed gates. An initialized S state is
121 citations
TL;DR: The spectral properties of the fluctuating Overhauser field in a GaAs double quantum dot are characterized by measuring correlation functions and power spectra of the rate of singlet-triplet mixing of two separated electrons, indicating that decoherence can be largely suppressed by echo techniques.
Abstract: In quantum dots made from materials with nonzero nuclear spins, hyperfine coupling creates a fluctuating effective Zeeman field (Overhauser field) felt by electrons, which can be a dominant source of spin qubit decoherence. We characterize the spectral properties of the fluctuating Overhauser field in a GaAs double quantum dot by measuring correlation functions and power spectra of the rate of singlet-triplet mixing of two separated electrons. Away from zero field, spectral weight is concentrated below 10 Hz, with approximately 1/f2 dependence on frequency f. This is consistent with a model of nuclear spin diffusion, and indicates that decoherence can be largely suppressed by echo techniques.
86 citations
TL;DR: The ability to electrically control spin dynamics in quantum dots makes them one of the most promising platforms for solid-state quantum information processing as discussed by the authors, and minimizing the influence of the nuclear spin environment is an important step towards realizing such promise.
Abstract: The ability to electrically control spin dynamics in quantum dots makes them one of the most promising platforms for solid-state quantum-information processing. Minimizing the influence of the nuclear spin environment is an important step towards realizing such promise.
11 citations
TL;DR: In this paper, a two-dimensional hole system using shallow etching and top gating was proposed for ballistic transport across a quantum point contact (QPC) defined in high-quality GaAs.
Abstract: We studied ballistic transport across a quantum point contact (QPC) defined in a high-quality GaAs (311)A two-dimensional hole system using shallow etching and top gating. The QPC conductance exhibits up to 11 quantized plateaus. The ballistic one-dimensional subbands are tuned by changing the lateral confinement and the Fermi energy of the holes in the QPC. We demonstrate that the positions of the plateaus (in gate voltage), the source-drain data, and the negative magnetoresistance data can be understood in a simple model that takes into account the variation, with gate bias, of the hole density and the width of the QPC conducting channel.
5 citations
TL;DR: In this article, a two-dimensional (2D) hole system using shallow etching and top-gating was studied, where the ballistic one-dimensional subbands were tuned by changing the lateral confinement and the Fermi energy of the holes in the QPC.
Abstract: We studied ballistic transport across a quantum point contact (QPC) defined in a high-quality, GaAs (311)A two-dimensional (2D) hole system using shallow etching and top-gating. The QPC conductance exhibits up to 11 quantized plateaus. The ballistic one-dimensional subbands are tuned by changing the lateral confinement and the Fermi energy of the holes in the QPC. We demonstrate that the positions of the plateaus (in gate-voltage), the source-drain data, and the negative magneto-resistance data can be understood in a simple model that takes into account the variation, with gate bias, of the hole density and the width of the QPC conducting channel.
3 citations