Quantum entanglement and excitonic spectra in InGaAs/GaAs dot molecules
Abstract
The small size of semiconductor quantum dots drives speculation that they may provide a physical representation of a quantum bit (qubit) that supports a superposition of ``0'' and ``1''. In one possible realization, two qubits A and B are represented by a hole and an electron. The two different states of the qubits are given by their occupation probability, either occupying the top (T) or the bottom (B) dot of a selfassembled dotmolecule. The use of this system as a quantum register requires the ability to store entangled exciton states. We present an atomistic theory of dot molecule spectra based on correlated pseudopotential calculations of an exciton in a pair of vertically stacked InGaAs/GaAs dots. Competing effects of strain, geometry, and band mixing lead to many unexpected features missing in contemporary models. The first four excitonic states are all optically active at small interdot separation. We quantify the degree of entanglement of the exciton wave functions and show its sensitivity to interdot separation. At a critical distance (d_c=8.5 nm for our dot) the entanglement reaches a maximum of 80%. We suggest ways to spectroscopically identify the entangled exciton states.
 Publication:

APS March Meeting Abstracts
 Pub Date:
 March 2004
 Bibcode:
 2004APS..MARH36003B