202
6 Effects of Quantisation
118], which emits light from a condensate formed in the ground state. In addition,
polariton microcavities exposed to external fields offer rich possibilities to study the
properties of polariton (spinor) condensates (summarised for instance in [119]), e.g.
when polariton scattering rates are altered and the spin degeneracy of the groundstate is lifted due to a Zeeman splitting at elevated magnetic fields [112, 120, 121].
This can have for example an impact on the photon statistics (cf. Fig. 3.10), polarisation degree, or show a nonequilibrium spin-Meissner effect, understood as the
suppression of superfluidity up to a critical magnetic field proportional to the polariton concentration [122].
Much more can be done with quantum-well systems or other 2D configurations,
such as 2D electron gases (2DEGs), than can be summarised in short here using
examples from laser and cavity–polaritons research. In addition, the use of naturally
formed ultrathin 2D systems is also highly attractive for nanoelectronic applications, and for quantum information processing (reviewed for instance in [123]). To
overcome limitations imposed by continuous miniaturisation efforts to keep up with
Moore’s law, new concepts are envisioned to reach beyond that point where mere
shrinking of the channel size results in higher transistor densities and computational
performance. 2D-material field-effect transistors [124, 125] promise such a path, but
also the achievement of flexible nanoelectronics [126, 127] and novel concepts such
as neuromorphic transistors for brain-inspired cognitive systems [128, 129], to name
but a few.
Photodetectors and sensors based on graphene and graphene-related-materials
are already heavily explored (see for instance [130]). Recently, such detectors have
also been functionalised with colloidal quantum dots (cQDs, typically core–shell
nanoparticles) that are deposited on the gate-tunable graphene channel of its fieldeffect transistor. While graphene absorbs little but over a wide range of wavelengths,
quantum dots have a very narrow optical resonance related to 0D excitons with high
oscillator strength. Due to the aforementioned size-dependence of the confinement
energy (6.7), their optical band gap is easily tunable over a wide range for a fixed
material system. However, cQDs also suffer from broadening of emission lines due to
surface states and electronic defects, and these nanoclusters commonly need ligands
for stabilisation, in order to prevent bunching in solution (not detailed here). Such
hybrid scheme uses the spectrally tunable and usually strong photon absorption of
cQDs in combination with charge- or energy-transfer processes to the underlying
graphene layer for high-mobility photocurrent extraction, as studied for example in
[131] with regard to gate-tunable Förster transfer (cf. Fig. 2.8).
These selected topics of quantum-structure and quantum-materials applications
show some use of prominent quantum systems and their typical advantages. Certainly,
towards the establishment of chip-integrated photonics for next generation highspeed optical computing and communications, photonic circuitries will strongly benefit from quantum-physical design principles and structure concepts realised on the
nanoscale. Ultimately, based on quantum structures and devices, all-optical computers and quantum computers are envisioned, as discussed in the quantum-technology
literature [8–10, 123].
6 Effects of Quantisation
118], which emits light from a condensate formed in the ground state. In addition,
polariton microcavities exposed to external fields offer rich possibilities to study the
properties of polariton (spinor) condensates (summarised for instance in [119]), e.g.
when polariton scattering rates are altered and the spin degeneracy of the groundstate is lifted due to a Zeeman splitting at elevated magnetic fields [112, 120, 121].
This can have for example an impact on the photon statistics (cf. Fig. 3.10), polarisation degree, or show a nonequilibrium spin-Meissner effect, understood as the
suppression of superfluidity up to a critical magnetic field proportional to the polariton concentration [122].
Much more can be done with quantum-well systems or other 2D configurations,
such as 2D electron gases (2DEGs), than can be summarised in short here using
examples from laser and cavity–polaritons research. In addition, the use of naturally
formed ultrathin 2D systems is also highly attractive for nanoelectronic applications, and for quantum information processing (reviewed for instance in [123]). To
overcome limitations imposed by continuous miniaturisation efforts to keep up with
Moore’s law, new concepts are envisioned to reach beyond that point where mere
shrinking of the channel size results in higher transistor densities and computational
performance. 2D-material field-effect transistors [124, 125] promise such a path, but
also the achievement of flexible nanoelectronics [126, 127] and novel concepts such
as neuromorphic transistors for brain-inspired cognitive systems [128, 129], to name
but a few.
Photodetectors and sensors based on graphene and graphene-related-materials
are already heavily explored (see for instance [130]). Recently, such detectors have
also been functionalised with colloidal quantum dots (cQDs, typically core–shell
nanoparticles) that are deposited on the gate-tunable graphene channel of its fieldeffect transistor. While graphene absorbs little but over a wide range of wavelengths,
quantum dots have a very narrow optical resonance related to 0D excitons with high
oscillator strength. Due to the aforementioned size-dependence of the confinement
energy (6.7), their optical band gap is easily tunable over a wide range for a fixed
material system. However, cQDs also suffer from broadening of emission lines due to
surface states and electronic defects, and these nanoclusters commonly need ligands
for stabilisation, in order to prevent bunching in solution (not detailed here). Such
hybrid scheme uses the spectrally tunable and usually strong photon absorption of
cQDs in combination with charge- or energy-transfer processes to the underlying
graphene layer for high-mobility photocurrent extraction, as studied for example in
[131] with regard to gate-tunable Förster transfer (cf. Fig. 2.8).
These selected topics of quantum-structure and quantum-materials applications
show some use of prominent quantum systems and their typical advantages. Certainly,
towards the establishment of chip-integrated photonics for next generation highspeed optical computing and communications, photonic circuitries will strongly benefit from quantum-physical design principles and structure concepts realised on the
nanoscale. Ultimately, based on quantum structures and devices, all-optical computers and quantum computers are envisioned, as discussed in the quantum-technology
literature [8–10, 123].