Spectral asymmetries in the resonance fluorescence of two-level systems under pulsed excitation

Abstract

We present an open-system master equation study of the coherent and incoherent resonance fluorescence spectrum from a two-level quantum system under coherent pulsed excitation. Several pronounced features which differ from the fluorescence under a constant drive are highlighted, including a multi-peak structure and a pronounced off-resonant spectral asymmetry, in stark contrast to the conventional symmetrical Mollow triplet. We also study semiconductor quantum dot systems using a polaron master equation, and show how the key features of dynamic resonance fluorescence change with electron-acoustic-phonon coupling.The theory of resonant scattering of light from a twolevel system (TLS) is a major achievement in quantum optics and provides an experimentally accessible gateway to probing strong-field quantum optics. In recent decades, advances in the ability to coherently manipulate atomic systems with light has allowed for a breadth of technological innovations which harness the quantum mechanical properties of these systems [1]. Furthermore, quantum dots (QDs) -semiconductor materials confined in three dimensions, with excited electron-hole pairs (excitons) mimicking the behaviour of an excited atom, can serve as "artificial atoms", maintaining the physics of the quantized system's interaction with the electromagnetic field, but with tunable properties and potential for scalability [2]. Semiconductor QDs have been the subject of much recent research for their potential as sources of quantum light, particularly single and entangled photons [3]. While constant excitation with a continuous wave (cw) laser drive can be used to create a TLS singlephoton source, often technological proposals require a deterministic source -one that can be triggered on-demand. This is typically done by an optical pulse, which renders resonance fluorescence (RF) of a TLS a genuine timedependent quantum dynamical process.The usual features of the RF spectrum under strong cw excitation manifest as the so-called Mollow triplet [4], where the power spectrum of the scattered field takes on a characteristic three-peak resonance structure due to radiative transitions between eigenstates of the system Hamiltonian, as well as a delta function peak at the (monochromatic) drive frequency corresponding to coherent elastic scattering. However, under excitation by a short pulse, the RF spectrum can take on features which obscure or eliminate this characteristic spectrum, especially under off-resonant excitation. The pulsed RF spectrum has been studied theoretically in atomic systems [5][6][7][8][9][10], and more recently in QD-cavity systems for on-resonance excitation [11], where a dynamic spectrum has been observed in the presence of cavity coupling [12].In this Letter, we describe the unique features of pulsed * c.gustin@queensu.ca RF spectra in depth using a master equation approach, and explore the different effects under time-dependent excitation, which are of interest to emerging experimental studies of pulsed quantum optical systems. In particul...

Nonadiabatic effects in periodically driven dissipative open quantum systems

“…Additional broadened peaks consistent with the Floquet spectrum arise due to the periodic modulation and may destructively interfere as is for example seen in the missing main peak in the case of the sign-change protocol (top). Similar features in the power spectrum have been reported in [40] for a qubit subject to a pulsed excitation. G 1 (|τ |, τ c ) * .…”

High-resolution spectroscopy of a quantum dot driven bichromatically by two strong coherent fields

“…As expected, with increasing drive strength of the second laser, similar spectra compared to the resonant scenario are observed, while the asymmetry for small α c is increased. In contrast to the single drive offresonant Mollow triplet, which is symmetrical in the absence of pure dephasing, there is a strong inherent asymmetry in the Mollow-like spectrum for small but nonzero α c , which persists in our simulations even with γ = 0 (not shown) [30]. While dephasing generically broadens spectral peaks, it will also in general affect the relative spectral weights of differing peaks; pure dephasing in a bare-state basis appears as non-radiative dissipation when viewed in the system (Floquet) eigenbasis, which can violate the principle of detailed balance and thus generically changes the distribution of spectral weights (peak areas) [30].…”

“…In contrast to the single drive offresonant Mollow triplet, which is symmetrical in the absence of pure dephasing, there is a strong inherent asymmetry in the Mollow-like spectrum for small but nonzero α c , which persists in our simulations even with γ = 0 (not shown) [30]. While dephasing generically broadens spectral peaks, it will also in general affect the relative spectral weights of differing peaks; pure dephasing in a bare-state basis appears as non-radiative dissipation when viewed in the system (Floquet) eigenbasis, which can violate the principle of detailed balance and thus generically changes the distribution of spectral weights (peak areas) [30]. Specifically, for the regimes studied in this work, we do find in our simulations that dephasing will slightly change the distribution of spectral weights, but this effect is generally insignificant to qualitatively affect our plots, and largely serves to broaden the spectral linewidths.…”

“…We also confirm suppression of spectral lines due to quantum interference and coupling to subharmonic resonances which has already been studied by He et al [14] and observe additional features of the fluorescence spectrum, including the formation of triplets centered at higher multiples of the Rabi energy of the driving laser. Furthermore, by driving the QD under a similar excitation scenario but with an offresonant primary laser, we observe similar spectral features as the resonant case but with heightened inherent spectral asymmetry, in contrast to the (pure dephasing free) monochromatic case [30].…”

Time-dependent spectra of a three-level atom in the presence of electron shelving

“…A slight asymmetry occurs in the detuned case that vanishes in the long time limit [15]; in this case one of the sidebands is closer to the atomic resonance and is larger than the other [15], while the asymmetry in the center of the spectrum gets smaller (see inset). More pronounced spectral asymmetries are found, for example, in detuned pulsed laser resonance fluorescence [28].…”