Model of the Optical Emission of a Driven Semiconductor Quantum Dot: Phonon-Enhanced Coherent Scattering and Off-Resonant Sideband Narrowing

Abstract

We study the crucial role played by the solid-state environment in determining the photon emission characteristics of a driven quantum dot. For resonant driving, we predict a phonon-enhancement of the coherently emitted radiation field with increasing driving strength, in stark contrast to the conventional expectation of a rapidly decreasing fraction of coherent emission with stronger driving. This surprising behaviour results from thermalisation of the dot with respect to the phonon bath, and leads to a nonstandard regime of resonance fluorescence in which significant coherent scattering and the Mollow triplet coexist. Off-resonance, we show that despite the phonon influence, narrowing of dot spectral sideband widths can occur in certain regimes, consistent with an experimental trend.PACS numbers: 78.67. Hc, As described by Mollow, the spectrum of light scattered from a resonantly driven two-level system (TLS) depends crucially on the relative size of the laser driving strength to the TLS radiative decay rate [1]. For weak driving, the light is predominately coherently (or elastically) scattered, resulting in a single (delta function) peak in the emission spectrum at the laser frequency. At larger driving strengths, however, coherent scattering is strongly suppressed, and the emission becomes dominated by incoherent (inelastic) scattering from the TLSlaser dressed states [2]. This results in a triple-peak structure in the spectrum, known as the Mollow triplet.While these fundamental predictions have long been confirmed in the traditional quantum optical setting of driven atoms [3], interest has turned more recently to their observation in solid-state TLSs (artificial atoms) such as semiconductor quantum dots (QDs) [4][5][6][7][8][9][10], single molecules [11], and superconducting circuits [12]. In the particular case of QDs, many of the archetypal features of atomic quantum optics have now been demonstrated, such as resonance fluorescence [4][5][6][7][8][9][10], coherent population oscillations [7,[13][14][15], photon anti-bunching [16,17], and two-photon interference [18][19][20]. Aside from being of fundamental interest, these observations also pave the way towards using QDs as efficient single photon sources [21][22][23][24], and for other quantum technologies [25].Thus, under appropriate conditions, the emission properties of a driven QD can bear close resemblance to the more idealised case of a driven atom in free space. QDs are, nevertheless, unavoidably coupled to their surrounding solid-state environments. For coherentlydriven (ground state) excitonic transitions in typical arsenide QDs, coupling to acoustic phonons has been demonstrated to dominate the QD-environment interaction [14,15], leading to the appearance of an excitationinduced dephasing contribution with a rate that varies with the square of the Rabi frequency (dot-laser coupling strength) [9,14,15,26]. This driving dependence is theoretically understood as resulting from phonons that induce transitions between the dressed states of the QD at...

Two-photon interference from a quantum dot microcavity: Persistent pure dephasing and suppression of time jitter

“…We attribute pure dephasing in our sample as caused by exciton-phonon coupling and spectral fluctuation of the QD energy levels on a time scale shorter than the pulse separation of 12.2 ns. The constant pure-dephasing rate used in our theory is expected to well approximate the spectral fluctuations, but the influence of phonons is known to give rise to more complicated behavior [28][29][30][31]. In particular, differing phonon absorption and emission rates at low temperatures are expected to lead to asymmetries for positive and negative detuning [29].…”

Engineering a squeezed phonon reservoir with a bichromatic driving of a quantum dot

“…In practice this may well be a reasonable assumption. For example, the radiative recombination time of the exciton, determined by 1/Γ, is usually 500 − 800 ps [11,21]. The Liouvillian (22) has a structure analogous to the damping of a two-level system by a squeezed reservoir.…”

“…A number of different situations have been investigated [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. These include experimental studies of the effect of phonons on the Rabi oscillations, Autler-Townes splitting, and the Mollow triplet of the fluorescence field emitted by a driven quantum dot [16][17][18][19][20][21][22][23][24].…”

Imaginary echoes

“…Highly directional emission is crucial to the overall efficiency of the source, and is typically achieved by either placing the QD in a waveguide with low out-of-plane scattering 15,16 , or by coupling resonantly to an optical cavity mode [6][7][8][9]12,13 . Nevertheless, the solid-state nature of QDs leads to strong coupling between the electronic degrees of freedom and their local environment; fluctuating charges 17 , nuclear spins 18,19 , and lattice vibrations [20][21][22][23] all lead to a suppression of photon coherence and a resulting reduction in indistinguishability 11,[24][25][26][27] . While early experiments were indeed limited by these factors [6][7][8][9] , improvements in fabrication and resonant excitation techniques have steadily increased photon indistinguishability to levels now exceeding 99% in resonantly coupled QD-cavity systems 12,13 .…”