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Physical Review Letters

Ramsey Fringes in an Electric-Field-Tunable Quantum Dot System

Stefan Stufler, Patrick Ester, A. Zrenner, Max Bichler A

Published Jan 25, 2006• 50 citations
Publisher

Abstract

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.

DOI
10.1103/physrevlett.96.037402

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One of the criteria for the physical implementation of quantum computing is that it must be possible to manipulate individual qubits to prepare them in the same well-defined state. In schemes involving linear optics and single photons from self-assembled quantum dots, this requirement can be intractable as quantum dots form with a distribution of emission energies. We have designed a structure based on InAs quantum dots embedded at the center of an AlGaAs/GaAs/AlGaAs quantum well which facilitates carrier confinement under application of electric fields up to |F| = 500 kVcm -1. This is an order of magnitude greater than previous reports. Through the quantum-confined Stark effect, individual dots can be tuned by up to 25meV, three orders of magnitude greater than their linewidth. This unprecedented tuning range allows many quantum dots to be tuned to the same energy with ease, enabling us to carry out two-photon interference measurements using remote quantum dots. Furthermore, we demonstrate scalability by performing the interference experiment with three pairs of quantum dots. By post-selecting events where two photons arrive simultaneously at a beamsplitter, we find that the interference visibility is limited only by the timing resolution of our system. We also performed measurements as a function of energy detuning which showed that maximum visibility can only be achieved when the dots are degenerate in energy. This opens up the possibility of transferring quantum information between remote solid-state systems.
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