Ultrafast quantum optics with solid state nanosystems

Semiconductor quantum dots

Semiconductor quantum dots are one of the most promising candidates for implementing robust qubits in quantum information processing. The possibility to optically initialize, manipulate and read out the charge and spin state on ultrafast timescales makes them very attractive. We use femtosecond pump-probe experiments to study the ultrafast dynamics in single semiconductor quantum dots [1].

Metal nanoantennas

To reach the limit of only a single photon manipulating a single electron in a quantum dot the coupling of light with a wavelength of a few hundred nanometers into the object of nanometer dimensions has to be optimized. We mainly study two nanophotonic elements to reach this goal: dielectric microcavities [2, 3] and metallic nanoantennas [4, 5].

Color centers in diamond

Alternatively, we investigate color centers in diamond. Since their first optical characterization on a single emitter level, they have been used as robust single-photon sources. We optically study these nanoscopic light emitters, which operate at room-temperature [6, 7]. Photonic nanostructures are designed and fabricated to increase light coupling.

Atomically thin semiconductors

Graphene is an exceptional two-dimensional material, but a zero band gap semiconductor. In contrast, a monolayer of MoS2 has a band gap and emits photons in the visible regime. We have shown that MoSe2 and WSe2 also shine bright in monolayer form [8]. We found bright and stable single-photon emitters in monolayer WSe2 [9] and could position them on the nanoscale [10]. We coupled a metal nanoantenna to atomically thin WS2 and enhanced the photoluminescence by one order of magnitude [11]. We elucidated the ultrafast valley dynamics for atomically thin WS2 [12]. We tuned the excitons in monolayer WSe2 with uniaxial strain [13]. We studied monolayers in high magnetic fields: we measured the g-factor of excitons in monolayer MoTe2 [14] and explained the magnetic-field-induced rotation of polarized light emission from monolayer WS2 [15] .

[1] F. Sotier et al., Nature Phys. 5, 352 (2009)

[2] M. Kahl et al, Nano Lett. 7, 2897 (2007)

[3] T. Thomay et al., Opt. Expr. 16, 9791 (2008)

[4] J. Merlein et al., Nature Photon. 2, 230 (2008)

[5] T. Hanke et al., Phys. Rev. Lett. 103, 257404 (2009)

[6] G. Balasubramanian et al., Nature 455, 648 (2008)

[7] K. Beha et al., Phys. Rev. Lett., 109, 097404 (2012)

[8] P. Tonndorf et al., Opt. Expr. 21, 4908 (2013)

[9]  P. Tonndorf et al., Optica 2, 347 (2015)

[10] J. Kern et al., Advanced Materials 28, 7101 (2016)

[11] J. Kern et al., ACS Photonics 2, 1260 (2015)

[12] R. Schmidt et al., Nano Lett. 16, 2945 (2016)

[13] R. Schmidt et al., 2D Materials 3, 021011 (2016)

[14] A. Arora et al., Nano Lett. 16, 3624 (2016)

[15] R. Schmidt et al., Phys. Rev. Lett., 117, 077402 (2016)