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arXiv:2406.04909 · Optica Quantum

Orchestrating time and color: a programmable source of high-dimensional entanglement

Laura Serino, Werner Ridder, Abhinandan Bhattacharjee, Jano Gil-López, Benjamin Brecht, Christine Silberhorn

Published Sep 3, 2024• 16 citations
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Abstract

High-dimensional encodings based on temporal modes (TMs) of photonic quantum states provide the foundations for a highly versatile and efficient quantum information science (QIS) framework. Here, we demonstrate a crucial building block for any QIS applications based on TMs: a programmable source of maximally entangled high-dimensional TM states. Our source is based on a parametric downconversion process driven by a spectrally shaped pump pulse, which facilitates the generation of maximally entangled TM states with a well-defined dimensionality that can be chosen programmatically. We characterize the effective dimensionality of the generated states via measurements of second-order correlation functions and joint spectral intensities, demonstrating the generation of bi-photon TM states with a controlled dimensionality in up to 20 dimensions.

DOI
10.1364/opticaq.532334

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High-dimensional encodings based on temporal modes (TMs) of photonic quantum states provide the foundations for a highly versatile and efficient quantum information science (QIS) framework. Here, we demonstrate a crucial building block for any QIS applications based on TMs: a programmable source of maximally entangled high-dimensional TM states. Our source is based on a parametric downconversion process driven by a spectrally shaped pump pulse, which facilitates the generation of maximally entangled TM states with a well-defined dimensionality that can be chosen programmatically. We characterize the effective dimensionality of the generated states via measurements of second-order correlation functions and joint spectral intensities, demonstrating the generation of bi-photon TM states with a controlled dimensionality in up to 20 dimensions.
Photon pairs produced by the pulse-pumped nonlinear parametric processes have been a workhorse of quantum information science (QIS). Engineering the spectral property of quantum states is crucial for practical QIS applications. However, photon pairs with desirable spectral properties are currently achieved with specially engineered optical hardware but with severely limited flexibility in tuning the spectral properties of the sources. Here, we demonstrate a spectrally programmable photon pair source by exploiting a two-stage nonlinear interferometer scheme with a computer-controlled phase device. The phase-control device can introduce phase shifts for spectral engineering by a programmable phase function that can be arbitrarily defined. When the phase function is properly designed, the output spectrum of the source can be freely customized and changed without replacing any hardware component in the system. Using this approach, we are able to program photon pairs with factorable positively correlated and negatively correlated spectra. In addition, we also realize a source of multi-dimensional three-channel spectrally factorable photon pairs. Our investigation provides a flexible and powerful new approach for engineering the mode profile of photon pairs and should find wide applications in QIS.
High-dimensional quantum information processing promises capabilities beyond the current state of the art, but addressing individual information-carrying modes presents a significant experimental challenge. Here we demonstrate effective high-dimensional operations in the time-frequency domain of nonclassical light. We generate heralded photons with tailored temporal-mode structures through the pulse shaping of a broadband parametric down-conversion pump. We then implement a quantum pulse gate, enabled by dispersion-engineered sum-frequency generation, to project onto programmable temporal modes, reconstructing the quantum state in seven dimensions. We also manipulate the time-frequency structure by selectively removing temporal modes, explicitly demonstrating the effectiveness of engineered nonlinear processes for the mode-selective manipulation of quantum states.
The time-frequency degree of freedom is a powerful resource for implementing high-dimensional quantum information processing. In particular, field-orthogonal pulsed temporal modes offer a flexible framework compatible with both long-distance fibre networks and integrated waveguide devices. In order for this architecture to be fully utilised, techniques to reliably generate diverse quantum states of light and accurately measure complex temporal waveforms must be developed. To this end, nonlinear processes mediated by spectrally shaped pump pulses in group-velocity engineered waveguides and crystals provide a capable toolbox. In this review, we examine how tailoring the phasematching conditions of parametric downconversion and sum-frequency generation allows for highly pure single-photon generation, flexible temporal-mode entanglement, and accurate measurement of time-frequency photon states. We provide an overview of experimental progress towards these goals, and summarise challenges that remain in the field.
Precise manipulation of the time–frequency modes of entangled photons is crucial for future quantum science and technologies. Recently, the frequency-domain-quantum-optical-synthesis (FD-QOS) method was demonstrated by creating a superposition of different joint temporal amplitudes: those temporal distributions can be controlled by manipulating the joint spectral amplitude in 2D frequency space via a Fourier optical relation. This FD-QOS method provides an efficient, flexible, and easy-to-control way to precisely modulate the temporal distributions of the entangled photon in an ultrafast region. However, manipulation of only the temporal modes is not sufficient for various applications in quantum information, since spectral modulations are also needed on many occasions. Here, we present a proof-of-concept experiment of two-photon spectral modulation via temporal manipulation of a biphoton wave packet. This protocol, called time-domain-quantum-optical-synthesis (TD-QOS), is achieved by adjusting the relative phases between two joint temporal distributions. In addition, the two-photon joint spectral distributions are characterized by measuring the joint spectral intensities and Hong–Ou–Mandel interferences. The combination of FD-QOS and TD-QOS enables complete control over the biphoton states. Our work would further develop quantum technologies that rely on the time–frequency modes of entangled photons.
High-dimensional encoding in time-frequency and photon-number degrees of freedom promises photon-efficient quantum communication, but requires detectors that are both temporal-mode selective and photon-number resolving. Here we demonstrate time-correlated single-photon detection combining both capabilities. A train of shaped pump pulses drives quantum frequency up-conversion to select a chosen temporal mode, and the converted photons are counted with a photon-number-resolving detector. Applying to a photon-pair source by spontaneous parametric downconversion into signal and idler bands, we demonstrate direct sampling of the high-dimensional correlated quantum states on compound time-frequency and photon number bases. Our measurements show that the up-converted photons in each band exhibit thermal photon-number statistics, indicating strong single-mode selection. We reconstruct joint temporal intensities conditioned on one and two photon pairs, revealing signal-idler correlations in both time-frequency and photon number. Together, these results establish a unified technology framework linking high-dimensional quantum correlations, mode-selective photon measurement, and photon-number resolved detection. This approach provides a route to characterizing multimode photon-pair sources and to larger time-frequency and photon-number alphabets for high-dimensional quantum communication and information processing.
High-dimensional encoding in time-frequency and photon-number degrees of freedom promises photon-efficient quantum communication, but requires detectors that are both temporal-mode selective and photon-number resolving. Here we demonstrate time-correlated single-photon detection combining both capabilities. A train of shaped pump pulses drives quantum frequency up-conversion to select a chosen temporal mode, and the converted photons are counted with a photon-number-resolving detector. Applying to a photon-pair source by spontaneous parametric downconversion into signal and idler bands, we demonstrate direct sampling of the high-dimensional correlated quantum states on compound time-frequency and photon number bases. Our measurements show that the up-converted photons in each band exhibit thermal photon-number statistics, indicating strong single-mode selection. We reconstruct joint temporal intensities conditioned on one and two photon pairs, revealing signal-idler correlations in both time-frequency and photon number. Together, these results establish a unified technology framework linking high-dimensional quantum correlations, mode-selective photon measurement, and photon-number resolved detection. This approach provides a route to characterizing multimode photon-pair sources and to larger time-frequency and photon-number alphabets for high-dimensional quantum communication and information processing.