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Journal of Modern Optics

Coherent control of single quantum dot exciton embedded in a photodiode

Roman S. Kolodka, A. J. Ramsay, P. W. Fry, W. K. Ng, A. Tahraoui, Huiyun Liu, M. Hopkinson, A. M. Fox, Maurice S. Skolnick

Published Aug 15, 2007• 0 citations
Publisher

Abstract

We study the coherent properties of a two-level system based on the ground state neutral exciton of a single InGaAs self-assembled quantum dot (SAQD) embedded in an n-i-Schottky diode. By using a photocurrent technique, we observe Rabi oscillations of the exciton population for pulse-areas of up to 6π. We perform two pulse quantum interference experiments to deduce the decoherence rate.

DOI
10.1080/09500340701345650

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We study the coherent properties of a two-level system based on the ground state neutral exciton of a single InGaAs self-assembled quantum dot (SAQD) embedded in an n-i-Schottky diode. By using a photocurrent technique, we observe Rabi oscillations of the exciton population for pulse-areas of up to 6π. We perform two pulse quantum interference experiments to deduce the decoherence rate.
Abstract In a single self‐assembled InGaAs quantum dot, the one‐exciton ground‐state transition defines a two‐level system, which appears as an extremely narrow resonance of only a few μeV width. The resonant interaction of this two‐level system with cw laser fields can be studied in detail by photocurrent spectroscopy, revealing the fine structure of the excitonic ground state as well as the effects of nonlinear absorption and power broadening. For the case of pulsed laser fields and in the absence of decoherence, the two‐level system represents a qubit. Excitations with ps laser pulses result in qubit rotations, which appear as Rabi oscillations in photocurrent experiments. Double pulse experiments further allow us to infer the decoherence time and to perform coherent control on a two level system.
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We developed a high-resolution Michelson interferometer with a He–Ne two-frequency laser positioning system, and measured the coherent carrier dynamics of a single InAs self-assembled quantum dot (SAQD) using a micro-spectroscopy system. The phase-locked double pulses were stabilized, with the maximum deviation being below 10 nm during the long measurement time of 1 h. Using this system, coherent control of an exciton in an InAs SAQD with very fine phase stabilization was demonstrated. The dephasing time of the single quantum dots was 9.5 ps which is close to that estimated from the homogeneous linewidth in the photoluminescence excitation (PLE) spectrum.
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 $n\text{\ensuremath{-}}i$ Schottky diode. We excite 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 are compared to a numerical simulation of the system.
We develop a realistic model of Rabi oscillations in a quantum-dot photodiode. Based in a multiexciton density matrix formulation we show that for short pulses the two-level model fails and higher levels should be taken into account. This affects some of the experimental conclusions, such as the inferred efficiency of the state rotation (population inversion) and the deduced value of the dipole interaction. We also show that the damping observed cannot be explained using constant rates with fixed pulse duration. We demonstrate that the damping observed is in fact induced by an off-resonant excitation to or from the continuum of wetting layer states. Our model describes the nonlinear decoherence behavior observed in recent experiments.