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Quantum Electronics and Laser Science Conference

An optically induced and detected Bell-like state in a single quantum dot

Gang Chen, E. T. Batteh, Xiaoqin Li, Duncan G. Steel, Dan Gammon, Lu Jeu Sham

Published Jun 25, 2003• 0 citations
Publisher

Abstract

Summary form only given. A single quantum dot (QD) exciton is considered as a basic unit capable of carrying one bit of quantum information (qubit). Reference has demonstrated exciton Rabi oscillations in single QD's that are equivalent to single-bit rotations. To realize two-bit quantum logic operations in the next step, it is essential to identify and coherently manipulate two interacting single QD excitons. Our earlier work shows that two-exciton entangled states not involving the biexciton can be optically induced. This paper extends the entanglement to include the biexciton and show that all four basis states of the two-exciton system can be coherently manipulated based on a coherent nonlinear optical spectroscopy technique.

DOI
10.1109/qels.2002.1031154

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Summary form only given. A single quantum dot (QD) exciton is considered as a basic unit capable of carrying one bit of quantum information (qubit). Reference has demonstrated exciton Rabi oscillations in single QD's that are equivalent to single-bit rotations. To realize two-bit quantum logic operations in the next step, it is essential to identify and coherently manipulate two interacting single QD excitons. Our earlier work shows that two-exciton entangled states not involving the biexciton can be optically induced. This paper extends the entanglement to include the biexciton and show that all four basis states of the two-exciton system can be coherently manipulated based on a coherent nonlinear optical spectroscopy technique.
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Optically induced entanglement is identified by the spectrum of the phase-sensitive homodyne-detected coherent nonlinear optical response in a single gallium arsenide quantum dot. The electron-hole entanglement involves two magneto-excitonic states differing in transition energy and polarization. The strong coupling needed for entanglement is provided through the Coulomb interaction involving the electrons and holes. The result presents a first step toward the optical realization of quantum logic operations using two or more quantum dots.
We report coherent optical control of a biexciton (two electron-hole pairs), confined in a single quantum dot, that shows coherent oscillations similar to the excited-state Rabi flopping in an isolated atom. The pulse control of the biexciton dynamics, combined with previously demonstrated control of the single-exciton Rabi rotation, serves as the physical basis for a two-bit conditional quantum logic gate. The truth table of the gate shows the features of an all-optical quantum gate with interacting yet distinguishable excitons as qubits. Evaluation of the fidelity yields a value of 0.7 for the gate operation. Such experimental capability is essential to a scheme for scalable quantum computation by means of the optical control of spin qubits in dots.
Transient nonlinear optical spectroscopy, performed on excitons confined to single GaAs quantum dots, shows oscillations that are analogous to Rabi oscillations in two-level atomic systems. This demonstration corresponds to a one-qubit rotation in a single quantum dot which is important for proposals using quantum dot excitons for quantum computing. The dipole moment inferred from the data is consistent with that directly obtained from linear absorption studies. The measurement extends the artificial atom model of quantum dot excitonic transitions into the strong-field limit, and makes possible full coherent optical control of the quantum state of single excitons using optical pi pulses.
Summary form only given. We use transient nonlinear optical spectroscopy to demonstrate Rabi oscillations between each of the dipole coupled states, corresponding to qubit rotations. The interface fluctuation GaAs quantum dots are probed with sub-micron spatial resolution. The resonant excitation of the biexciton requires a two-color scheme in a hyper Raman gain configuration. To demonstrate exciton Rabi oscillations, the laser wavelength is fixed at the exciton resonance. Exciton and biexciton Rabi oscillations correspond to qubit rotations of the |00> to |01> or |10> state and the |01> or |10> to |11> state respectively, depending on the polarization of the excitation field.