62
3 Light–Matter Interactions for Photonic Applications
Fig. 3.1 Schematic diagram of two distinct light–matter coupling regimes for emitter–cavity systems. The optical microcavity (light field) and the embedded quantum emitter (two-level system)
are indicated in the centre. When the cavity mode C and the exciton mode X are resonant, they can
couple either strongly (left panel) or weakly (right panel). The boxes at the sides represent the exciton quasi-particle picture in which cavity light interacts with matter (coupling strength indicated).
For low oscillator strength ( f osc ) and low resonator quality factor Q cav , the coupling strength is
typically not enough to achieve a reversible energy transfer within the lifetime of cavity photons
prior to their leakage through one of the resonator mirrors. If the coupling strength g is considerably larger than the decay rates for field γ C and emitter γ X , Rabi oscillations between the field and
emitter populations with frequency 2 occur and new eigen-states are formed, the polariton modes
(energy split by 2g = 2 = LP/UP , with the Rabi frequency). Thus, for the two regimes,
different spectral (and temporal) features are obtained: polariton energy–momentum dispersion
branches with anticrossing behaviour (usually damped oscillations due to decay channels), or a
Purcell effect with crossing modes (and irreversible decay, whereas the spontaneous emission rate
is enhanced/suppressed for resonant/off-resonant detunings, respectively)
ent energy exchange between the emitter and photon states with pronounced spatial and spectral resonance (see Fig. 3.1)
2 —promising various applications [14, 15].
Microcavity-based single-photon sources and nanolasers were a subject of intense
studies in the last two decades [12, 16–27] and have left their mark on modern
quantum cryptography concepts and light source achievements [28–31].
From Light-Dressed Matter States to Polariton Lasers
Intriguing light–matter states were demonstrated in the single emitter regime [22,
32, 33], and (actively altered) Rabi oscillations have been even monitored in the transient polariton luminescence [34, 35] or transient cavity reflection [36] with ultrafast
spectroscopy techniques, which furthermore allow the manipulation of the quantum
states via ultrashort optical [34, 35] or THz pulses [36]. Particularly, the light effective mass of polaritons in high-quality microcavities gave rise to the observation of
dynamic BEC in solids [37–40] (also see [41–46] on the condensation of polaritons,
and related discussions on this subject [47]), from which electrically-driven polariton
lasers were later obtained [48–50]. More about polariton lasers is found for instance
in the foundational papers [51, 52] or in newer literature [7, 53–58]. In addition,
2 Ultimately, at the quantum limit, coupling of a single exciton with the vacuum light field in an
empty cavity is obtained, leading to a vacuum Rabi splitting between the new eigen-states of the
strongly-coupled system.
3 Light–Matter Interactions for Photonic Applications
Fig. 3.1 Schematic diagram of two distinct light–matter coupling regimes for emitter–cavity systems. The optical microcavity (light field) and the embedded quantum emitter (two-level system)
are indicated in the centre. When the cavity mode C and the exciton mode X are resonant, they can
couple either strongly (left panel) or weakly (right panel). The boxes at the sides represent the exciton quasi-particle picture in which cavity light interacts with matter (coupling strength indicated).
For low oscillator strength ( f osc ) and low resonator quality factor Q cav , the coupling strength is
typically not enough to achieve a reversible energy transfer within the lifetime of cavity photons
prior to their leakage through one of the resonator mirrors. If the coupling strength g is considerably larger than the decay rates for field γ C and emitter γ X , Rabi oscillations between the field and
emitter populations with frequency 2 occur and new eigen-states are formed, the polariton modes
(energy split by 2g = 2 = LP/UP , with the Rabi frequency). Thus, for the two regimes,
different spectral (and temporal) features are obtained: polariton energy–momentum dispersion
branches with anticrossing behaviour (usually damped oscillations due to decay channels), or a
Purcell effect with crossing modes (and irreversible decay, whereas the spontaneous emission rate
is enhanced/suppressed for resonant/off-resonant detunings, respectively)
ent energy exchange between the emitter and photon states with pronounced spatial and spectral resonance (see Fig. 3.1)
2 —promising various applications [14, 15].
Microcavity-based single-photon sources and nanolasers were a subject of intense
studies in the last two decades [12, 16–27] and have left their mark on modern
quantum cryptography concepts and light source achievements [28–31].
From Light-Dressed Matter States to Polariton Lasers
Intriguing light–matter states were demonstrated in the single emitter regime [22,
32, 33], and (actively altered) Rabi oscillations have been even monitored in the transient polariton luminescence [34, 35] or transient cavity reflection [36] with ultrafast
spectroscopy techniques, which furthermore allow the manipulation of the quantum
states via ultrashort optical [34, 35] or THz pulses [36]. Particularly, the light effective mass of polaritons in high-quality microcavities gave rise to the observation of
dynamic BEC in solids [37–40] (also see [41–46] on the condensation of polaritons,
and related discussions on this subject [47]), from which electrically-driven polariton
lasers were later obtained [48–50]. More about polariton lasers is found for instance
in the foundational papers [51, 52] or in newer literature [7, 53–58]. In addition,
2 Ultimately, at the quantum limit, coupling of a single exciton with the vacuum light field in an
empty cavity is obtained, leading to a vacuum Rabi splitting between the new eigen-states of the
strongly-coupled system.