Quantum Dot Nanomaterials for Quantum Memories
We demonstrate the potential of semiconductor quantum dot nanomaterials for a solid-state based controllable quantum memory.
Light is a promising candidate for carrying information in both, classical and quantum communication systems. So far, concepts and realizations of quantum memory elements have typically been based on atom and ion ensembles and various investigations have concentrated on atomic vapors or ensembles of atoms. Indeed, the transfer of a quantum state between matter and light has been achieved. The realization of a quantum memory systems requires precise knowledge of the coherence properties of the particular material employed and the system itself.
Due to their narrow spectral linewidths and rapid radiative decay rates semiconductor quantum dots have become promising candidates for the transformation of quantum states of light to quantum states of matter. Furthermore, they can easily be integrated into larger structures to improve efficiency which makes them a key tool in the development of light-based quantum technologies.
We explore the potential of semiconductor QD nanomaterials for a solid-state based controllable quantum memory. We concentrate on the situation displayed in Fig 1: The dot ensemble (material system InGaAs) is organized in a two-dimensional layer that is optically excited by a light signal representing the carrier of quantum information.
Fig1: Scheme of the optical excitation of the quantum dot system in vertical-cavity configuration. (r,t1) and (r', t2) visualize the storage of information in r and the dynamic transverse transfer of information (r → r′).
Fig.2 Snapshots of the carrier density (a), field-field correlation (b) and field-dipole correlation (c) in the optically excited QD ensemble after the injection of a light pulse: The excitation leads to a wave-like radial dynamics in the distributions.
We use quantum luminescence equations [1] that combine a fully microscopic description of all relevant coherent and incoherent materials properties with a space-time theory of field-field correlations and field-dipole correlations representing the origin of space-time coherence.
Simulations reveal that high coupling of spatial and temporal degrees of freedom is a key requirement
for coherence transfer and/or storage and discuss the influence of disorder. They prove that this configuration may lead to wave-like radial signal propagation or to the trapping of coherence.
Spectral detuning of the signal pulse and input power is proposed as a powerful means of controlling quantum dot quantum memories.
[1] E. Gehrig and O. Hess, E. Gehrig and O. Hess. Spatio-Temporal Dynamics and Quantum Fluctuations in Semiconductor Lasers (Springer, Heidelberg 2003)
