4.3 Quantum Optics
117
dependence on high-quality microresonators. Moderately high Q-factors in the range
of a few hundred up to 1000 can be enough to obtain strong coupling. This allows one
to employ various tunable-cavity concepts (cf. [206, 207, 223]). With optical cavities
such as those proposed in [224], the material independent continuous adjustability of
cavity resonances could be utilised for polariton-based chemistry allowing a precise
adjustment of the polariton energy levels [225]. Furthermore, they could also become
useful for an efficient study of chemical reactions influenced by different light–matter
coupling situations.
One motivation to employ such open tunable microcavities is given by the investigation of the transition between weak and strong coupling by smoothly tuning the
coupling strength [224] (see Fig. 4.8). Therefor two concepts have been discussed and
simulated that could allow one to probe this interesting transition situation, since the
two coupling regimes are linked by an exceptional point (EP). According to the literature, such point, at which only one complex solution exists for the coupled-oscillator
system, brings up exotic phenomena [226–228], including chiral behaviour [229]
and topological energy transfer between the two coupled modes [230]. Moreover,
EPs in optical microcavity systems are understood to enhance sensing [231] due to
the sharp transition between the coupling regimes.
Prospects of Open Tunable Microcavity Systems
While typically monolithic cavities are used for polariton research, tunable cavities
such as in [206, 207, 223] not only allow to flexibly set the cavity length,
13 they
also provide experimental access to the intracavity space which can be used for coupling experiments with nanosheets (see proposed tunable-coupling experiment in
[224]), colloidal quantum emitters, molecules, dispersed particles or particles in a
polymer matrix (cf. [223]), or even for coupling between the resonator-light field
and two different emitter systems inside the cavity (e.g. [232]). Thus, tunable open
microresonators qualify for numerous experiments, including opto-mechanical coupling experiments such as in [233, 234] (which were also intended for 2D materials
through works by the author and his students), and can be conveniently used in
connection with 2D, 1D and 0D excitonic systems.
Polariton Research on Solid Foundations
The enrichment of knowledge throughout recent work further facilitated the study of a
variety of polariton systems under optical and electrical excitation, e.g.
Esaki-diodes [235], 1D polariton gases in microcavity wires [236], electroluminescence from polariton traps [237], as well as the study of condensates in textured
landscapes [238, 239]. Further examples about the technological realisation of various polariton systems are found in [240].
The acquired background in polariton physics also enabled the author of this work
to investigate together with cooperation partners on the nature of spinor condensates
[142, 143], and to use correlation experiments [143, 145] and magnetic fields [142,
143, 147, 202] to alter the exciton–polariton system’s dynamics and features. In
13 In experiments, tuning of the cavity length (i.e. mirror position) is practically done via piezoelectric actuators, which can provide positioning control on the nm scale.
117
dependence on high-quality microresonators. Moderately high Q-factors in the range
of a few hundred up to 1000 can be enough to obtain strong coupling. This allows one
to employ various tunable-cavity concepts (cf. [206, 207, 223]). With optical cavities
such as those proposed in [224], the material independent continuous adjustability of
cavity resonances could be utilised for polariton-based chemistry allowing a precise
adjustment of the polariton energy levels [225]. Furthermore, they could also become
useful for an efficient study of chemical reactions influenced by different light–matter
coupling situations.
One motivation to employ such open tunable microcavities is given by the investigation of the transition between weak and strong coupling by smoothly tuning the
coupling strength [224] (see Fig. 4.8). Therefor two concepts have been discussed and
simulated that could allow one to probe this interesting transition situation, since the
two coupling regimes are linked by an exceptional point (EP). According to the literature, such point, at which only one complex solution exists for the coupled-oscillator
system, brings up exotic phenomena [226–228], including chiral behaviour [229]
and topological energy transfer between the two coupled modes [230]. Moreover,
EPs in optical microcavity systems are understood to enhance sensing [231] due to
the sharp transition between the coupling regimes.
Prospects of Open Tunable Microcavity Systems
While typically monolithic cavities are used for polariton research, tunable cavities
such as in [206, 207, 223] not only allow to flexibly set the cavity length,
13 they
also provide experimental access to the intracavity space which can be used for coupling experiments with nanosheets (see proposed tunable-coupling experiment in
[224]), colloidal quantum emitters, molecules, dispersed particles or particles in a
polymer matrix (cf. [223]), or even for coupling between the resonator-light field
and two different emitter systems inside the cavity (e.g. [232]). Thus, tunable open
microresonators qualify for numerous experiments, including opto-mechanical coupling experiments such as in [233, 234] (which were also intended for 2D materials
through works by the author and his students), and can be conveniently used in
connection with 2D, 1D and 0D excitonic systems.
Polariton Research on Solid Foundations
The enrichment of knowledge throughout recent work further facilitated the study of a
variety of polariton systems under optical and electrical excitation, e.g.
Esaki-diodes [235], 1D polariton gases in microcavity wires [236], electroluminescence from polariton traps [237], as well as the study of condensates in textured
landscapes [238, 239]. Further examples about the technological realisation of various polariton systems are found in [240].
The acquired background in polariton physics also enabled the author of this work
to investigate together with cooperation partners on the nature of spinor condensates
[142, 143], and to use correlation experiments [143, 145] and magnetic fields [142,
143, 147, 202] to alter the exciton–polariton system’s dynamics and features. In
13 In experiments, tuning of the cavity length (i.e. mirror position) is practically done via piezoelectric actuators, which can provide positioning control on the nm scale.