On the Identification of Intervalence-Band Coherences in Semiconductor Quantum Wells

Raman Coherence Beats from Entangled Polarization Eigenstates in InAs Quantum Dots

“…A second field E 2 , separated from E 1 by a variable delay t, generates a nonlinear polarization to third order in the applied fields, which in turn radiates the nonlinear signal of interest. This signal field copropagates with E 2 , and is homodyne-detected with this field on a square-law detector [16,26]. Details of this differential transmission (DT) setup can be found in [27].…”

“…This coherence is especially important for applications to quantum logic devices [14,15] that also require coherent optical control of entangled states. Manipulation and detection of this coherence, in the dipole approximation, is nonlinear in the applied optical fields, and its detection in the time domain is enabled by detecting the time evolution of the relative phase associated with the two quantum probability amplitudes [16].In this paper, we report the observation of the time evolution of the nonradiative Raman coherence induced between the two fine-structure split polarization eigenstates in an ensemble of SAQD's, and demonstrate the ability to optically induce and detect the resultant quantum entangled states. The quantum coherence is observed through homodyne detection of the emitted radiation arising from four-wave mixing which reports directly on the time evolution of the relative phase between the two states.…”

“…This coherence is especially important for applications to quantum logic devices [14,15] that also require coherent optical control of entangled states. Manipulation and detection of this coherence, in the dipole approximation, is nonlinear in the applied optical fields, and its detection in the time domain is enabled by detecting the time evolution of the relative phase associated with the two quantum probability amplitudes [16].…”

“…The final excitation sequence is called the coherent excitation pathway and has no contribution from population dynamics. The time evolution detected in this experimental geometry reports on the time evolution of the second order contribution r 01,10 [16,26] which corresponds to the excited state wave function given by jc͘ C 10 j10͘ 1 C 01 j01͘, an entangled state involving the coherent superposition of the two different polarization eigenstates of the exciton. The oscillation in time corresponds to the energy splitting of these two states, and the decay of the oscillation corresponds to the decoherence of the superposition state.…”

“…Because of the use of the phase sensitive technique, the temporal evolution of r 10,01 can be observed and manifests itself as oscillations at the energy splitting, DE xy (Fig. 1), in the time domain [16,26]. Figure 3(a) shows the oscillation of the Raman coherence for E 1 and E 2 having circular polarizations of either the same (SCP) or opposite (OCP) helicity, chosen to coherently excite both polarization eigenstates.…”