Coherent Optical Writing and Reading of the Exciton Spin State in Single Quantum Dots

Y. Benny, S. Khatsevich, Y. Kodriano, E. Poem, R. Presman, D. Galushko, P. M. Petroff, and D. Gershoni

Phys. Rev. Lett. 106, 040504 – Published 25 January 2011

Abstract

We demonstrate a one-to-one correspondence between the polarization state of a light pulse tuned to neutral exciton resonances of single semiconductor quantum dots and the spin state of the exciton that it photogenerates. This is accomplished using two variably polarized and independently tuned picosecond laser pulses. The first “writes” the spin state of the resonantly excited exciton. The second is tuned to biexcitonic resonances, and its absorption is used to “read” the exciton spin state. The absorption of the second pulse depends on its polarization relative to the exciton spin direction. Changes in the exciton spin result in corresponding changes in the intensity of the photoluminescence from the biexciton lines which we monitor, obtaining thus a one-to-one mapping between any point on the Poincaré sphere of the light polarization to a point on the Bloch sphere of the exciton spin.

Received 27 September 2010

DOI:https://doi.org/10.1103/PhysRevLett.106.040504

Authors & Affiliations

Y. Benny¹, S. Khatsevich¹, Y. Kodriano¹, E. Poem¹, R. Presman¹, D. Galushko¹, P. M. Petroff², and D. Gershoni^1,*

¹The Physics Department, Technion—Israel Institute of Technology, Haifa, 32000, Israel
²Materials Department, University of California Santa Barbara, California, 93106, USA

^*dg@physics.technion.ac.il

Article Text (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand

Issue

Vol. 106, Iss. 4 — 28 January 2011

Reuse & Permissions

Access Options

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
(a) Schematic description of the writing and reading processes. Horizontal lines describe the states’ energies. The spin wave functions of these states are depicted to the left. $↑$ ( $⇓$ ) represents spin up (down) electron (hole). The blue (red) arrow represents carrier in the ground (excited) energy level. Upward (green) arrows denote resonantly tuned light pulses; first, short (long) to a ground (excited) exciton and second, to an excited biexciton state. Curled downward arrows denote nonradiative relaxation and a blue (red) downward arrow radiative $H$ ( $V$ ) polarized recombination. The linewidth of the laser pulses are given by the curves to the right. (b) A Bloch sphere representation of the exciton spin state initiated by the polarized laser pulse. The point $P_{0} (θ, ϕ)$ represents an arbitrarily polarized spin state. $A$ and $I_{0}$ , relate to the biexciton PL intensity [see Fig. 3a].Reuse & Permissions
Figure 2
(a) $V$ (red) and $H$ (blue) polarized PL spectra from the resonantly excited QD. (b) [(c)] Polarization-sensitive PLE spectra of the exciton [biexciton]. (c) was obtained while resonantly exciting the exciton as indicated by the green vertical arrow in (b). For the readout the second laser was tuned to the biexciton resonance marked by the vertical green arrow in (c), while the PL was monitored from the $X X^{0}$ doublet as marked by the downward purple arrow in (a).Reuse & Permissions
Figure 3
(a) Emission intensity of the PL from the biexciton spectral lines as a function of the delay time between the pulse into the excited exciton resonance and the pulse into the biexciton resonance, for various pulse polarizations. The points are measured data and the solid curves are guides to the eye. The first (second) letter describes the polarization of the first (second) pulse. The phase and amplitude of the oscillations are related to the polarization of the first pulse [see Fig. 1b]. The phase differences between the various curves are summarized in the inset to (b). (b) Similar to (a) but for various polarizations of the first laser pulse and fixed $R$ second pulse. (c) Similar to (b) but here the first pulse is tuned directly to the ground exciton states.Reuse & Permissions
Figure 4
(a) [(b)] Biexciton doublet PL intensity (locked-in to the second laser) as a function of the polarization angle $ϕ$ [ $θ$ ] as defined in (c), for $D$ (triangles) and for $V$ (circles) polarized readout pulses. $Δ τ$ between the two pulses was $T = 122 ps$ .Reuse & Permissions

Physical Review Letters