Coupling and Entangling of Quantum States in Quantum Dot Molecules

Abstract

We demonstrate coupling and entangling of quantum states in a pair of vertically aligned, self-assembled quantum dots by studying the emission of an interacting electron-hole pair (exciton) in a single dot molecule as a function of the separation between the dots. An interaction-induced energy splitting of the exciton is observed that exceeds 30 millielectron volts for a dot layer separation of 4 nanometers. The results are interpreted by mapping the tunneling of a particle in a double dot to the problem of a single spin. The electron-hole complex is shown to be equivalent to entangled states of two interacting spins.

Optical Properties of Star-Shaped Gold Nanoparticles

“…2 The synthesis of branched quantum dots 3 could enable studies of entangled quantum states and quantum information processing within individual nanoparticles. 4 Metallic nanoparticles also benefit from the formation of complex structures. Magnetic "barcode" nanowires that contain periodic domains of NiFe/Cu 5 and Pt/Cu 6 offer tunable magnetic properties.…”

The role of phonons for exciton and biexciton generation in an optically driven quantum dot

“…Because of the similarity of this states with bonding or antibonding states these structures are also named QD molecules. This coupling, which can be controlled to a large degree by an external electric field, has been the subject of a large amount of work over the past years investigating both excitonic [103,104,105] and biexcitonic transitions [106,107]. In particular close to a resonance between spatially direct and indirect exciton states phonon-induced transitions can be strongly enhanced [108,73,109,110], which can also be interpreted as phonon-assisted tunneling [111,112].…”

Four-wave mixing in coupled semiconductor quantum dots

“…One of the crucial difficulties in these studies is the unavoidable inhomogeneous line broadening because of dot size fluctuations, inherent to any self-assembly growth procedure, which hinders the direct observation of interdot-coupling induced level splittings. Although the investigation of single quantum-dot molecules has been demonstrated and has given clear evidence of interdot coupling [11,12], the underlying analysis faces severe problems when the change of interdot coupling is accompanied by possible variations of the lateral confinement-a delicate problem in particular for the technologically highly relevant self-assembled dots.In this paper we present a theoretical analysis of fourwave mixing (FWM) [20] in an ensemble of inhomogeneously broadened coupled quantum dots, and we show that FWM spectra provide a sensitive measure of such pertinent interdot couplings. This finding rests on a number of nontrivial observations.…”

“…For the biexciton transitions, a clear signature of interdot-coupling appears in the spectra. Few-particle states in optically excited semiconductor quantum dots [1 -3] have recently attracted enormous interest: on the one hand, they exhibit a number of atomic-like properties attributed to their zero-dimensional nature, such as ultranarrow emission peaks [4,5] or ultralong dephasing times [6]; on the other hand, the semiconductor compound gives rise to a number of novel features which lack atomic counterparts, among which multi-excitons [7 -10] and flexible interdot coupling [11,12] are the most prominent ones. Optical excitations in semiconductors quantum dots are composed of electron -hole pairs (excitons), which become profoundly renormalized because of the resulting mutual Coulomb interactions; indeed, such Coulomb-renormalization effects have been studied exhaustively in single-dot spectroscopy [13] and are at the heart of the celebrated quantum-dot-based single-photon sources [14,15].…”