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arXiv:2608.28470

Input-Output Analysis of Quantum Dot SUPER Excitation

Johannes Kerber, Christoph Hotter, Helmut Ritsch, Klaus Mølmer

quant-phphysics.opticsSubmitted Aug 28, 2026• Announced Aug 31, 2026• 0 citations
arXivHTMLPDF

Abstract

The Swing-UP of the quantum EmitteR population (SUPER) two-color pulsed excitation scheme allows for robust and close to 100\% excitation of a two-level quantum emitter using only red detuned light. We analyze the underlying counterintuitive dynamics using a full quantum input-output description of the in- and outgoing light pulses for the case of two coherent free-space input pulses at realistic photon numbers. At the microscopic level, the SUPER mechanism exhibits its nonlinear three-photon Raman-type character, leading to a net photon-number change of $-2$ in one mode and $+1$ in the other, as was first guessed from cavity-enhanced model descriptions at low photon numbers. We confirm that in free space, a sufficiently high pulse photon number, much larger than one, is required to achieve high-fidelity inversion. To treat the large coherent-state amplitudes (photon numbers) relevant for SUPER, we extend the quantum input-output formalism to include a cumulant expansion approach. With an interaction-picture formulation, the few exchanged photons that govern the nontrivial dynamics enable direct full-quantum calculations in truncated Hilbert spaces, including treatments in a displacement frame and for initial Fock-state pulses.

Comments
12 pages including appendices, 9 figures and 1 table

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The Swing-UP of the quantum EmitteR population (SUPER) two-color pulsed excitation scheme allows for robust and close to 100% excitation of a two-level quantum emitter using only red detuned light. We analyze the underlying counterintuitive dynamics using a full quantum input-output description of the in- and outgoing light pulses for the case of two coherent free-space input pulses at realistic photon numbers. At the microscopic level, the SUPER mechanism exhibits its nonlinear three-photon Raman-type character, leading to a net photon-number change of −2-2−2 in one mode and +1+1+1 in the other, as was first guessed from cavity-enhanced model descriptions at low photon numbers. We confirm that in free space, a sufficiently high pulse photon number, much larger than one, is required to achieve high-fidelity inversion. To treat the large coherent-state amplitudes (photon numbers) relevant for SUPER, we extend the quantum input-output formalism to include a cumulant expansion approach. With an interaction-picture formulation, the few exchanged photons that govern the nontrivial dynamics enable direct full-quantum calculations in truncated Hilbert spaces, including treatments in a displacement frame and for initial Fock-state pulses.
In the SUPER scheme (Swing-UP of the quantum EmitteR population), excitation of a quantum emitter is achieved with two off-resonant, red-detuned laser pulses. This allows the generation of high-quality single photons without the need of complex laser stray light suppression or careful spectral filtering. In the present work, we extend this promising method to quantum emitters, specifically semiconductor quantum dots, inside a resonant optical cavity. A significant advantage of the SUPER scheme is identified in that it eliminates re-excitation of the quantum emitter by suppressing photon emission during the excitation cycle. This, in turn, leads to almost ideal single-photon purity, overcoming a major factor typically limiting the quality of photons generated with quantum emitters in high-quality cavities. We further find that for cavity-mediated biexciton emission of degenerate photon pairs, the SUPER scheme leads to near-perfect biexciton initialization with very high values of polarization entanglement of emitted photon pairs. Published by the American Physical Society 2024
The quest for the perfect single-photon source includes finding the optimal protocol for exciting the quantum emitter. Coherent optical excitation was, up until now, achieved by tuning the laser pulses to the transition frequency of the emitter, either directly or in average. Recently, it was theoretically discovered that an excitation with two red-detuned pulses is also possible where neither of which would yield a significant upper-level population individually. We show that the so-called swing-up of quantum emitter population (SUPER) scheme can be implemented experimentally with similar properties to existing schemes by precise amplitude shaping of a broadband pulse. Because of its truly off-resonant nature, this scheme has the prospect of powering high-purity photon sources with superior photon count rate.
To coherently control a few-level quantum emitter, typically pulses with an energy resonant to the transition energy are applied, making use of the Rabi mechanism, while a single off-resonant pulse does not result in a population inversion. Surprisingly, a two-color excitation with a combination of two off-resonant pulses is able to invert the system. In this paper, we provide an in-depth analysis of two-color excitation schemes within the dressed-state picture. We show that such schemes can be understood as a driving of the transition between the dressed states. In the two-level system this allows us to derive analytic expressions for the pulse parameters yielding a population inversion. We relate our findings to the Swing-UP of quantum EmitteR population (SUPER) mechanism, where the two pulses are red detuned. Our interpretation also holds in the case where one pulse is red detuned while the other pulse is blue detuned, as in dichromatic excitation schemes. We extend our considerations of the SUPER mechanism to the three-level system, where a strong mixing between the bare states takes place. The insights gained from these results help in finding accessible regimes for further experimental realizations of two-color excitation schemes.
The swing-up of quantum emitter population (SUPER) scheme allows to populate the excited state of a quantum emitter with near-unity fidelity using two red-detuned laser pulses. Its off-resonant yet fully coherent nature has attracted significant interest in quantum photonics as a valuable tool for preparing single-photon sources in their excited state on demand while simultaneously ensuring straightforward spectral filtering of the laser. However, the physical understanding of this mechanism in terms of energy exchange between the electromagnetic field and the emitter is still lacking. Here, we present a fully quantized model of the swing-up excitation and demonstrate that it is in fact a multi-photon process, where one of the modes loses two or more photons while the other gains at least one. Our findings provide an unexpected physical interpretation of the SUPER scheme and unveil a new non-linear interaction between single emitters and multiple field modes.
The swing-up of quantum emitter population (SUPER) scheme allows to populate the excited state of a quantum emitter with near-unity fidelity using two red-detuned laser pulses. Its off-resonant, yet fully coherent nature has attracted significant interest in quantum photonics as a valuable tool for preparing single-photon sources in their excited state on demand, while simultaneously ensuring straightforward spectral filtering of the laser. However, the physical understanding of this mechanism in terms of energy exchange between the electromagnetic field and the emitter is still lacking. Here, we present a fully quantized model of the swing-up excitation and demonstrate that it is in fact a multi-photon process, where one of the modes loses two or more photons while the other gains at least one. Our findings provide an unexpected physical interpretation of the SUPER scheme and unveil a new non-linear interaction between single emitters and multiple field modes.
To fulfill the security requirements of quantum cryptography, photon number coherence (PNC) of single photon sources has recently become an important figure of merit. Quantum dots (QDs) embedded in photonic microcavities offer a mature source of single photons, of which many properties can be tuned by the use of different excitation protocols or parameters. We show that the Swing-UP of quantum EmitteR population (SUPER) scheme can significantly decrease the PNC of the emitted photon, compared to resonant excitation. The reason for this is a laser-induced Stark shift, which effectively decouples the QD from the cavity during the SUPER excitation. Our calculations account for environmental effects such as phonons and radiative losses.