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Preparation of non-classical photon states in laser-driven quantum-dot-cavity systems under the influence of acoustic phonons

Subject Area Theoretical Condensed Matter Physics
Term from 2019 to 2023
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 419036043
 
Final Report Year 2023

Final Report Abstract

With the help of numerically exact path integral methods we explored possibilities to manipulate photon states by laser excitations of a quantum dot embedded in a resonantor. Major goals were the targeted preparation of non-classical photon states and the question what role phonons play in such schemes. We developed, e.g., protocols that can be realized with current resources for the preparation of higher Fock- or Schrödinger-cat-states as well as for the realization of a photon storage and a scheme for time dependent changing the entanglement type or switching between entangled and non-entangled states. The excitation conditions also determine the strength of coherences between different photon number states, which turned out to be relevant for applications in quantum cryptography. Unexpectedly, we found that under certain circumstances higher degrees of entanglement can be reached with phonons than without. Positive phonon influences were also found in studies of single-photon sources of high purity, that were realized by phonon-assisted preparation of excitons where the emitted photons are spectrally separated from the exciting laser. However, in other cases phonons turn out to be problematic for applications. Phonons, e.g., destroy the photon number statistics of N -photon-bundle states. In permanently driven exciton-biexciton systems phonons induce a phase transition-like behavior: above a critical temperatur or field strength the entanglement of the emitted photons disappears completely. Further, we could identify a limiting influence of the finite pulse duration on the achievable degree of entanglement. Phonons enhance this limitation and introduce a temperature dependence. Since the path integral method developed by us does not make any approximation to the model, such as, e.g., a neglection of memory effects, we were able to quantify without prejudice the error introduced by using the quantum regression theorem (QRT). Using the QRT underestimates systematically indistinguishabilities of photons by up to 18%. The introduction of a new numerically exact algorithm termed Automated Compression of Environments (ACE) opens new perspectives for the simulation of quantum dissipative systems. ACE is distinguished by its high flexibility. ACE can deal simultaneously with multiple different environment influences on a microscopic level. Bosonic, Fermionic or spin-environments can be accounted for without restriction concerning the memory depth or the strength of the correlations. Gaussian and non-Gaussian environments can be treated as well as linear and non-linear or diagonal and non-diagonal system-bath couplings.

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