Excitation, manipulation and analysis of few-fermion systems on the elementary femtosecond timescale

In these experiments, the studies on ultrashort timescales are brought to the ultimate extreme of measurements on single electrons. The long-term objective of this work is the ultimate control of the quantum state of single electrons in solid-state nanostructures, as well as the generation of new quantum states of light fields, e.g. femtosecond laser pulses with selectable and well-defined photon numbers.

In highly sensitive experiments, the sample, e.g. a semiconductor quantum dot [1, 2, 3], is pumped by an ultrashort laser pulse and the induced transmission change is probed after a time tDelay. The temporal distance tDelay of pump and probe is adjusted with a delay stage and the according transient transmission spectra are recorded via a monochromator and CCD camera. To measure the state and the dynamics of a system, several spectra are taken at different time delays tDelay. The temporal resolution of the experiment is given by the pulse durations.

Figure 1: Scheme of the pump-probe setup. A two-color femtosecond fiber laser generates ultrashort light pulses at two independently tunable wavelengths. The temporal delay of pump and probe is adjusted with a delay stage before they are overlaid collinearly. The sample can be cooled down to 4 K in a Helium cryostat. The pump-induced transmission change is detected with a CCD coupled to a monochromator.

The light source for this experiment is an inherently low-noise Erbium fiber Laser [4, 5, 6, 7, 8, 9, 10], developed in our group. A single oscillator seeds two parallel amplifier stages that are independently frequency doubled. The average output power is around a few mW over the entire tuning range from 540 nm to 700 nm. The minimal pulse duration is 180 fs.

Figure 2: (left) Photograph of the independently tunable two-color output from the two-color Erbium:fiber laser. (right) Tuningrange of the two-color femtosecond fiber laser in the visible spectral region.

Adding single photons to fs laser pulses

The experiment described above enables the controlled addition of single photons to femtosecond laser pulses [11]. By aligning the electron spin of the sample and enhancing the light-matter interaction of sample and probe beam, precise manipulation of the lphoton number in a probe pulse by one single unit can be achieved. We use a 5 T magnet cryostat and various nanoplasmonic [12, 13, 14, 15] and photonic structures [16, 17, 18] to enhance light-matter coupling.

Figure 3: (left) Scanning electron micrograph of a micropillar. This photonic structure is produced via RF sputtering of TiO2 and SiO2 and subsequent milling via focused ion beam. (right) Scanning electron micrograph of different plasmonic structures. These structures are produced with electron beam lithography at a resolution down to 15 nm.


[1] R. Bratschitsch und A. Leitenstorfer
"Quantum dots: Artificial atoms for quantum optics"
Nature Mat. 5, 855-856 (2006)

[2] Y. Gao, S. Reischmann, J. Huber, T. Hanke, R. Bratschitsch, A. Leitenstorfer und S. Mecking
"Encapsulating of single quantum dots into polymer particles"
Colloid Polym. Sci. 286, 1329 (2008)

[3] G. Kiliani, R. Schneider, D. Litvinov, D. Gerthsen, M. Fonin, U. Rüdiger, A. Leitenstorfer und R. Bratschitsch
"Ultraviolet photoluminescence of ZnO quantum dots sputtered at room-temperature"
Opt. Express 19, 1641 (2011)

[4] F. Tauser, A. Leitenstorfer und W. Zinth
"Amplified femtosecond pulses from an Er:fiber system: Nonlinear pulse shortening and self-referencing detection of the carrier-envelope phase evolution"
Opt. Express 11, 594 (2003)

[5] F. Tauser, F. Adler und A. Leitenstorfer
"Widely tunable sub-30-fs pulses from a compact erbium-doped fiber source"
Opt. Lett. 29, 516 (2004)

[6] F. Adler, K. Moutzouris, A. Leitenstorfer, H. Schnatz, B. Lipphardt, G. Grosche und F. Tauser
"Phase-locked two-branch erbium-doped fiber laser system for long-term precision measurements of optical frequencies"
Opt. Express 12, 5872 (2004)

[7] F. Adler, A. Sell, F. Sotier, R. Huber und A. Leitenstorfer
"Attosecond relative timing jitter and 13 fs tunable pulses from a two-branch Er:fiber laser"
Opt. Lett. 32, 3504 (2007)

[8] A. Sell, G. Krauss, R. Scheu, R. Huber und A. Leitenstorfer
"8-fs pulses from a compact Er:fiber system: quantitative modeling and experimental implementation"
Opt. Express 17, 1070 (2009)

[9] G. Krauss, S. Lohss, T. Hanke, A. Sell, S. Eggert, R. Huber und A. Leitenstorfer
"Synthesis of a single cycle of light with compact erbium-doped fibre technology"
Nature Photon. 4, 33 (2010)

[10] G. Krauss, D. Fehrenbacher, D. Brida, C. Riek, A. Sell, R. Huber und A. Leitenstorfer
"All-passive phase locking of a compact Er:fiber laser system"
Opt. Lett. 36, 540 (2011)

[11] F. Sotier, T. Thomay, T. Hanke, J. Korger, S. Mahapatra, A. Frey, K. Brunner, R. Bratschitsch und A. Leitenstorfer
"Femtosecond few-fermion dynamics and deterministic single-photon gain in a quantum dot"
Nature Phys. 5, 352-356 (2009)

[12] J. Merlein, M. Kahl, A. Zuschlag, A. Sell, A. Halm, J. Boneberg, P. Leiderer, A. Leitenstorfer und R. Bratschitsch
"Nanomechanical control of an optical antenna"
Nature Photon. 2, 230 (2008)

[13] T. Hanke, G. Krauss, D. Träutlein, B. Wild, R. Bratschitsch und A. Leitenstorfer
"Efficient nonlinear light emission of single gold optical antennas driven by few-cycle near-infrared pulses"
Phys. Rev. Lett. 103, 257404 (2009) 

[14] V. Temnov, G. Armelles, U. Woggon, D. Guzatov, A. Cebollada, A. Garcia-Martin, J. Garcia-Martin, T. Thomay, A. Leitenstorfer und R. Bratschitsch
"Active magneto-plasmonics in hybrid metal–ferromagnet structures"
Nature Photon. 4, 107 (2010)

[15] A. Schell, G. Kewes, T. Hanke, A. Leitenstorfer, R. Bratschitsch, O. Benson und T. Aichele
"Single defect centers in diamond nanocrystals as quantum probes for plasmonic nanostructures"
Opt. Express 19, 7914 (2011)

[16] M. Kahl, T. Thomay, V. Kohnle, K. Beha, J. Merlein, M. Hagner, A. Halm, J. Ziegler, T. Nann, Y. Fedutik, U. Woggon, M. Artemyev, F. Perez-Willard, A. Leitenstorfer und R. Bratschitsch
"Colloidal quantum dots in all-dielectric high-Q pillar microcavities"
Nano Lett. 7, 2897 (2007) 

[17] T. Thomay, T. Hanke, M. Tomas, F. Sotier, K. Beha, V. Knittel, M. Kahl, K. M. Whitaker, D. R. Gamelin, A. Leitenstorfer und R. Bratschitsch
"Colloidal ZnO quantum dots in ultraviolet pillar microcavities"
Opt. Express 16, 9791 (2008)

[18] W.-M. Schulz, T. Thomay, M. Eichfelder, M. Bommer, M. Wiesner, R. Roßbach, M. Jetter, R. Bratschitsch, A. Leitenstorfer und P. Michler
"Optical properties of red emitting self-assembled InP/ (Al0.20Ga0.80)0.51In0.49P quantum dot based micropillars"
Opt. Express 18, 12543 (2010)

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