Coherence and Coupling of Single Quantum Dots

The coherence and coupling of semiconductor quantum dots (QDs) is receiving increasing attention due to possible solid-state implementations in the emerging field of quantum information processing.

Beside its fundamental interest, the knowledge of the dephasing time, inversely proportional to the homogeneous broadening, of an excitonic transition in a QD is of crucial importance for these applications. The dephasing time sets the time scale during which the coherence of the excitonic transition is preserved and therefore operations based on coherent-light matter interaction can occur. Moreover, it is strictly related to intrinsic mechanisms such as radiative processes, carrier-phonon scattering and carrier-carrier scattering.

Activities

The measurement of coherence in QD is typically performed on large ensembles to provide a measurable signal strength. We have developed a detection technique for coherent non-linear optical microscopy which can measure on individual QD's, called heterodyne spectral interferometry [3]. It allows to measure the four-wave mixing of individual excitons, and make images of them (see Figure).

The four-wave mixing in large ensembles creates an echo due to the phase-conjugation. In small ensembles of only a few QD's, the creation of this echo can be observed, deriving from constructive interference of the individual signals at the echo time, being random otherwise.

Coherent coupling mediated by a resonant optical cavity is specifically interesting, as it provides a tuneable coupling. We have shown this in [11].

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  Ffigur 3

Cyhoeddiadau

• Albert, F. et al., 2013. Microcavity controlled coupling of excitonic qubits. Nature Communications 4 1747. (10.1038/ncomms2764)
• Kasprzak, J. et al. 2010. Coherent coupling between distant excitons revealed by two-dimensional nonlinear hyperspectral imaging. Nature Photonics 5 (1), pp.57-63. (10.1038/nphoton.2010.284)
• Langbein, W. W. 2010. Coherent optical spectroscopy of semiconductor nanostructures. La Rivista del Nuovo cimento 33 (5), pp.255-312. (10.1393/ncr/i2010-10054-1)
• Kasprzak, J. and Langbein, W. W. 2009. Four-wave mixing from individual excitons: Intensity dependence and imaging. physica status solidi (b) 246 (4), pp.820-823. (10.1002/pssb.200880583)
• Borri, P. and Langbein, W. W. 2008. Transient four-wave mixing of excitons in quantum dots from ensembles and individuals. In: Benson, O. and Henneberger, F. eds. Semiconductor Quantum Bits. Singapore: Pan Stanford Publishing. , pp.269-319.
• Kasprzak, J. and Langbein, W. W. 2008. Vectorial four-wave mixing field dynamics from individual excitonic transitions. Physical Review. B, Condensed Matter and Materials Physics 78 (4) 041103(R). (10.1103/PhysRevB.78.041103)
• Langbein, W. W. and Patton, B. 2007. Transient coherent nonlinear spectroscopy of single quantum dots. Journal of Physics: Condensed Matter 19 (29) 295203. (10.1088/0953-8984/19/29/295203)
• Langbein, W. W. and Patton, B. 2006. Heterodyne Spectral Interferometry for Multidimensional Nonlinear Spectroscopy of Individual Quantum Systems. Optics Letters 31 , pp.1151-1153. (10.1364/OL.31.001151)
• Langbein, W. W. , Patton, B. and Woggon, U. 2005. Coherent Control and Polarization Readout of Individual Excitonic States. Physical Review Letters (PRL) 95 266401. (10.1103/PhysRevLett.95.266401)
• Langbein, W. W. and Patton, B. 2005. Microscopic Measurement of Photon Echo Formation in Groups of Individual Excitonic Transitions. Physical Review Letters (PRL) 95 17403. (10.1103/PhysRevLett.95.017403)

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Tîm y prosiect

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