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physica status solidi (b)

Ramsey fringes in a single InGaAs/GaAs quantum dot

Patrick Ester, Stefan Stufler, Steffen Michaelis de Vasconcellos, Max Bichler A, A. Zrenner

Published Jul 27, 2006• 1 citation
Publisher

Abstract

Abstract We report the observation of Ramsey fringes in single InGaAs/GaAs quantum dots. With double pulse p/2 excitation it is possible to control the occupancy and the phase of a quantum dot. The occupancy of the quantum dot oscillates with detuning. These Ramsey fringes are caused by a voltage dependent detuning of the QD. Due to the double pulse excitation the spectral sensitivity is strongly enhanced as compared to single pulse experiments. At long delay times we are able to resolve extremely narrow spectral fringes, clearly below the homogeneous linewidth of the underlying QD two level system. Our results demonstrate precision measurements on single quantum dots with strong implications for future quantum gates and quantum measurements. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

DOI
10.1002/pssb.200668028

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Abstract We report the observation of Ramsey fringes in single InGaAs/GaAs quantum dots. With double pulse p/2 excitation it is possible to control the occupancy and the phase of a quantum dot. The occupancy of the quantum dot oscillates with detuning. These Ramsey fringes are caused by a voltage dependent detuning of the QD. Due to the double pulse excitation the spectral sensitivity is strongly enhanced as compared to single pulse experiments. At long delay times we are able to resolve extremely narrow spectral fringes, clearly below the homogeneous linewidth of the underlying QD two level system. Our results demonstrate precision measurements on single quantum dots with strong implications for future quantum gates and quantum measurements. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
We report on Ramsey fringes measured in a single InGaAs/GaAs quantum dot two-level system. We are able to control the transition energy of the system by Stark effect tuning. In combination with double pulse excitation this allows for a voltage controlled preparation of the phase and the occupancy of the two-level system. For long pulse delay times we observe extremely narrow fringes with spectral width below the homogeneous linewidth of the system. Implications on quantum information processing are discussed.
Abstract We report on highly phase sensitive measurements with a slightly detuned excitation of a quantum mechanical two‐level system. It is formed by the single exciton ground state of a single quantum dot, which is incorporated in a n‐i‐Schottky diode. We excited the two‐level system by two partly overlapping laser pulses with variable phase shift. To investigate the properties of the quantum system we determine its occupancy by measuring the photocurrent. The experimental data is compared to a numerical simulation of the system. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
This thesis presents experiments carried out into the coherent properties of charge carriers confined within a single InGaAs/GaAs quantum dot. Specifically the ground state - single exciton qubit system is controlled with ultrafast optical pulses and then the population of the dot is measured by a high-sensitivity photocurrent detection technique. There are two principal results of these experiments, firstly by modulating the bias applied to the quantum dot diode, the detection efficiency of the photocurrent measurement technique is enhanced. The enhancement is possible as the modulated bias allows fast switching of the voltage-dependent carrier tunneling rates. Secondly, when the transition is addressed by an intense, positively detuned laser, the qubit system can be driven to a population inversion. This occurs due to phonon-assisted relaxation of the optical dressed states of the system. Here, the rapid thermalization due to the exciton-phonon interaction actually enables the population inversion, instead of simply being a source of decoherence.
Ramsey interference that enables careful control over quantum states is demonstrated here in an inhomogeneously broadened ensemble of quantum dots, which serve as the gain medium of a semiconductor waveguide operating at room temperature. A subfemtosecond-resolution pump-probe scheme reveals a clear oscillatory behavior of the amplitude and instantaneous frequency of the probe pulse. A unique phenomenon is also observed, whereby the temporal position of the output probe pulse also oscillates with the same periodicity. The latter cannot be observed in single-dot systems since it results from the distributed nature of the amplifier.