4.3 Quantum Optics
109
Fig. 4.4 Three regimes of operation and overview of the momentum-space signatures for a
polariton-laser diode with two-threshold behaviour (DC-operated quantum-well microcavity device
reported in [117]). From left to right, the current density j (particle density n) is increased to surpass
the first and the second threshold of the device, attributed to polariton lasing (polariton condensation)
and photon lasing (conventional VCSEL operation), respectively [117, 118] (further information
about polariton lasers can be found for instance in [119, 120]). Top: Here, sketches of the energy–
momentum dispersion relation in k for the lower polariton (LP) branch indicate the occupation
distribution below and above the condensation threshold density. A brief description of the two
distinct nonlinear regimes for such device is given in analogy to [116]. Bottom: Fourier-space
(far-field: FF) projection of the electrically-driven microcavity’s emission profile at corresponding
current densities, showing the relaxation bottleneck (a) in the linear polariton regime, as well as the
phase transitions towards a condensate (b, c) and photonic laser (d) with strongly narrowed far-field
signature. Adapted from [117]. Courtesy of the author
4.3 Quantum Optics
Within the field of quantum optics, cavity quantum electrodynamics (cQED) research
(see for instance [56, 149]) has grown to an important subject. It allows the exploration of fundamental light–matter coupling regimes and the development of novel
coherent (e.g. single-atom or polariton laser) as well as nonclassical light sources
(e.g. single-photon, squeezed-light or entangled photon-pair sources). Two important
regimes are that of weak coupling, where optical modes alter the emission properties
due to the Purcell effect [150], and that of strong coupling, for which the involved
modes hybridise to form new eigen-states and experience a periodic coherent energy
exchange (cf. [151]). Such system is characterised by Rabi oscillations [152] in the
time domain and a Rabi splitting in the frequency domain, first demonstrated for
quantum-well microcavities in 1992 [153].
109
Fig. 4.4 Three regimes of operation and overview of the momentum-space signatures for a
polariton-laser diode with two-threshold behaviour (DC-operated quantum-well microcavity device
reported in [117]). From left to right, the current density j (particle density n) is increased to surpass
the first and the second threshold of the device, attributed to polariton lasing (polariton condensation)
and photon lasing (conventional VCSEL operation), respectively [117, 118] (further information
about polariton lasers can be found for instance in [119, 120]). Top: Here, sketches of the energy–
momentum dispersion relation in k for the lower polariton (LP) branch indicate the occupation
distribution below and above the condensation threshold density. A brief description of the two
distinct nonlinear regimes for such device is given in analogy to [116]. Bottom: Fourier-space
(far-field: FF) projection of the electrically-driven microcavity’s emission profile at corresponding
current densities, showing the relaxation bottleneck (a) in the linear polariton regime, as well as the
phase transitions towards a condensate (b, c) and photonic laser (d) with strongly narrowed far-field
signature. Adapted from [117]. Courtesy of the author
4.3 Quantum Optics
Within the field of quantum optics, cavity quantum electrodynamics (cQED) research
(see for instance [56, 149]) has grown to an important subject. It allows the exploration of fundamental light–matter coupling regimes and the development of novel
coherent (e.g. single-atom or polariton laser) as well as nonclassical light sources
(e.g. single-photon, squeezed-light or entangled photon-pair sources). Two important
regimes are that of weak coupling, where optical modes alter the emission properties
due to the Purcell effect [150], and that of strong coupling, for which the involved
modes hybridise to form new eigen-states and experience a periodic coherent energy
exchange (cf. [151]). Such system is characterised by Rabi oscillations [152] in the
time domain and a Rabi splitting in the frequency domain, first demonstrated for
quantum-well microcavities in 1992 [153].