Quantum interferences of a single quantum dot in the case of detuning

We report on highly phase-sensitive measurements with a slightly detuned excitation of a quantum mechanical two-level system. It is formed by the single-exciton ground state of a single quantum dot, which is incorporated in a $n\text{−}i$ Schottky diode. We excite the two-level system by two partly overlapping laser pulses with variable phase shift. To investigate the properties of the quantum system we determine its occupancy by measuring the photocurrent. The experimental data are compared to a numerical simulation of the system.

Figure 1

(Color online) Measured photocurrent signal at resonant excitation for different pulse areas. The dashed line shows an excitation with two $\pi ∕2$ pulses. The solid line was recorded using two $0.8\pi$ pulses.

Figure 2

Measured photocurrent signal resulting from two $0.8\pi$ pulses at detuning of (a) 27 and (b) $47\mu \mathrm{eV}$.

Figure 3

Numerical simulation of a two-level system under detuned excitation. Starting from the resonant case (solid) the detuning increases from 50 (dashed), 130 (dash-dotted), 330 (dash-dot-dotted) up to $590\mu \mathrm{eV}$ (dotted).

Figure 4

(Color online) Final states on the Bloch sphere for (a) resonant excitation and (b) excitation $47\mu \mathrm{eV}$ detuned. With detuning the curve is rotated around the $w$ axis, tilted, and also slightly deformed.