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Journal of Optics

Enhanced two-photon absorption of frequency-entangled N00N states in type-I SPDC

Andrea T. Joseph, Roger Andrews

Published May 27, 2021• 0 citations
Publisher

Abstract

Abstract We study the two-photon absorption properties of frequency-entangled N00N states produced in a Hong-Ou-Mandel interferometer using type-I degenerate photon pairs, generated via spontaneous parametric down-conversion. By comparing our results with N00N states with no frequency entanglement, we demonstrate enhanced two-photon absorption due to frequency entanglement. We also derive an analytic expression for the enhancement factor which is found to be greater than one for all finite values of the ratio of the bandwidth of the pump to the bandwidth of the detected photons. We have also found suppression and enhancement in the two-photon absorption probabilities for specific time delays applied to the N00N states.

DOI
10.1088/2040-8986/ac05cf

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Abstract We study the two-photon absorption properties of frequency-entangled N00N states produced in a Hong-Ou-Mandel interferometer using type-I degenerate photon pairs, generated via spontaneous parametric down-conversion. By comparing our results with N00N states with no frequency entanglement, we demonstrate enhanced two-photon absorption due to frequency entanglement. We also derive an analytic expression for the enhancement factor which is found to be greater than one for all finite values of the ratio of the bandwidth of the pump to the bandwidth of the detected photons. We have also found suppression and enhancement in the two-photon absorption probabilities for specific time delays applied to the N00N states.
In this paper we examine the N-photon absorption properties of "N00N" states, a subclass of path entangled number states. We consider two cases. The first involves the N-photon absorption properties of the ideal N00N state, one that does not include spectral information. We study how the N-photon absorption probability of this state scales with N. We compare this to the absorption probability of various other states. The second case is that of two-photon absorption for an N = 2 N00N state generated from a type II spontaneous down conversion event. In this situation we find that the absorption probability is both better than analogous coherent light (due to frequency entanglement) and highly dependent on the optical setup. We show that the poor production rates of quantum states of light may be partially mitigated by adjusting the spectral parameters to improve their two-photon absorption rates. This work has application to quantum imaging, particularly quantum lithography, where the N-photon absorbing process in the lithographic resist must be optimized for practical applications.
Entangled photons exhibit strong nonclassical frequency and time correlations simultaneously, which allow them to excite and extract information about molecules in new ways compared to classical spectroscopy. In this report, we demonstrate the accessibility of entangled two-photon absorption (ETPA) as an analytical technique using CW-pumped type-I degenerate spontaneous parametric down-conversion. We made improvements to lower the noise, error, and limit of detection of the ETPA experiment. We prove and quantify frequency entanglement from the experimentally measured joint frequency spectrum using the Schmidt decomposition. As evidence of the ETPA process, we found a clear linear dependence of the ETPA and ETPA-induced fluorescence rates with the entangled input photon rate for all the studied chromophores. This ETPA experiment can be used to analyze a wide variety of chromophores of chemical and biological significance and shows potential for ETPA-induced fluorescence detection capabilities. As an application of our work, we show that one may control the population of specific excited states in molecules with the use of a spatial light modulator in the setup.
We demonstrate a new class of frequency-entangled states generated via spontaneous parametric down-conversion under extended phase-matching conditions. Biphoton entanglement with coincident signal and idler frequencies is observed over a broad bandwidth in periodically poled KTiOPO4. We demonstrate high visibility in Hong-Ou-Mandel interferometric measurements under pulsed pumping without spectral filtering, which indicates excellent frequency indistinguishability between the down-converted photons. The coincident-frequency entanglement source is useful for quantum information processing and quantum measurement applications.
This paper presents a theoretical study of the enhancement of Zou-Wang-Mandel (ZWM) interferometry through cavity-enhanced spontaneous parametric down-conversion (SPDC) processes producing frequency-entangled biphotons. The ZWM interferometry shows the capability to generate interference effects between single signal photons via indistinguishability between the entangled idler photons. This paper extends the foundational principles of ZWM interferometry by integrating cavity-enhanced SPDCs, aiming to narrow photon bandwidths for improved coherence and photon pair generation efficiency, which is critical for applications in quantum information technologies, quantum encryption, and quantum imaging. This work explores the theoretical implication of employing singly resonant optical parametric oscillators within the ZWM interferometer to produce narrow-band single photons. By combining cavity-enhanced SPDCs with ZWM interferometry, this study fills a gap in current theoretical proposals, offering significant advancements in quantum cryptography and network applications that require reliable, narrow-band single photons.
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High-rate entanglement generation is essential for the realization of practical quantum repeaters. To this end, frequency multiplexing of the photons employed is an effective approach. In particular, schemes using cavity-enhanced spontaneous parametric down-conversion (cSPDC) as a photon-pair source have been proposed. In this study, toward a theoretical performance evaluation of frequency-multiplexed quantum repeaters based on cSPDC, we derive an approximate expression for the quantum state of the frequency-multiplexed photons, where each frequency mode is treated as an independent two-mode squeezed vacuum (TMSV) state. Using this expression, we calculate the heralding probability and fidelity of entanglement generation for several cases in a single-photon interference scheme using frequency multiplexing with cSPDC. Our results demonstrate that by multiplexing approximately 100 modes, the heralding probability improves to approximately 98% for an elementary link distance LEL=25kmL_\mathrm{EL}=25 \mathrm{km}LEL​=25km, even in scenarios where the fidelity exceeds 0.9 across all modes. Furthermore, for LEL=100kmL_\mathrm{EL}=100 \mathrm{km}LEL​=100km, we show that the heralding probability, which was approximately 0.7% in the single-mode case, increases to about 38% under the condition that the fidelity remains 0.9 or higher. These analytical results demonstrate the effectiveness of employing cSPDC as a photon-pair source for quantum repeaters.