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International conference on fiber optics and photonics

Insignificance of Relative Time delay between Photons for a Ultrafast Two-photon Process

Amartya Bose, Debabrata Goswami

Published Jan 1, 2012• 0 citations
Publisher

Abstract

Exploring the possibility of temporally resolving dynamics in an ideal two-photon process (TPP) indicates that the existence of one-photon physical intermediate states is not a prerequisite for TPP. This study also sheds light on the phase dependence of TPP.
DOI
10.1364/photonics.2012.w1b.2

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In this theoretical study, we show how ultrafast electron–nuclear dynamics in a molecule can be monitored by two-photon absorption of time–energy entangled photon pairs generated by spontaneous parametric down-conversion with a narrow-band pump. The dynamics is tracked by a controllable signal-idler delay. Time correlation of the entangled photons enables an ultrafast measurement even with a monochromatic pump. The frequency anticorrelation of the photon pair allows the projection of the intermediate excited-state wavepacket onto an energy-selected vibrational level on a higher-lying electronic state with high energy resolution. Such joint high temporal and energy resolution is not possible with classical light. We demonstrate our scheme for a conical intersection model with four electronic states and two vibrational modes. The ultrafast nuclear wavepacket dynamics around the conical intersection is imprinted onto the time- and frequency-resolved entangled two-photon absorption signals. Electronic population dynamics is obtained by the frequency-integrated signal.
We develop and demonstrate a trainable temporal postprocessor (TPP) harnessing a simple but versatile machine learning algorithm to provide optimal processing of quantum measurement data subject to arbitrary noise processes for the readout of an arbitrary number of quantum states. We demonstrate the TPP on the essential task of qubit state readout, which has historically relied on temporal processing via matched filters in spite of their applicability for only specific noise conditions. Our results show that the TPP can reliably outperform standard filtering approaches under complex readout conditions, such as high-power readout. Using simulations of quantum measurement noise sources, we show that this advantage relies on the TPP’s ability to learn optimal linear filters that account for general quantum noise correlations in data, such as those due to quantum jumps, or correlated noise added by a phase-preserving quantum amplifier. Furthermore, we derive an exact analytic form for the optimal TPP weights: this positions the TPP as a linearly scaling generalization of matched filtering, valid for an arbitrary number of states under the most general readout noise conditions, all while preserving a training complexity that is essentially negligible in comparison with that of training neural networks for processing temporal quantum measurement data. The TPP can be autonomously and reliably trained on measurement data and requires only linear operations, making it ideal for field-programmable gate array implementations in circuit QED for real-time processing of measurement data from general quantum systems. Published by the American Physical Society 2024
Abstract The experimental advance on light–matter interaction into strong couplings has invalidated the Jaynes–Cummings model and brought the quantum Rabi model (QRM) to more relevance. The QRM only involves linear coupling via a single -photon process (SPP), while the nonlinear two -photon process (TPP) is weaker and conventionally neglected. However, we find a contrary trend that enhancing the linear coupling might not suppress the nonlinear effect more but backfire to trigger some collapse of linear characters. Indeed, in strong SPP couplings a tiny strength of the TPP may dramatically change properties of the system, like a symmetry spontaneous breaking. By extracting the ground-state phase diagram including both a SPP and TPP, we find the TPP in low frequency limit induces a quantum phase transition with continuity–discontinuity double faces, which split into two distinct transitions at finite frequencies and yields a triple point. Our analysis unveils a subtle SPP–TPP entanglement.