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arXiv:1810.03245 · Physical Review A

Multiplexing heralded single photons in orbital-angular-momentum space

Shi-Long Liu, Qiang Zhou, Zhi‐Yuan Zhou, Shi-Kai Liu, Yan Li, Yin‐Hai Li, Chen Yang, Zhao-Huai Xu, Guang‐Can Guo, Bao-Sen Shi

Published Jul 16, 2019• 11 citations
arXivHTMLPDF

Abstract

A heralded single-photon source (HSPS) with competitive single-photon purity and indistinguishability has become an essential resource for photonic quantum information processing. Here we propose a theoretical regime to enhance heralded single-photon generation by multiplexing the degree of freedom of orbital angular momentum (OAM) of down-converted entangled photon pairs emitted from a nonlinear crystal. Experimentally, a proof-of-principle experiment is performed through multiplexing three OAM modes. We achieve a $47%$ enhancement in the single-photon rate. A second-order autocorrelation function ${g}^{(2)}(0)<0.5$ ensures our multiplexed heralded single photons with good single-photon purity. We further indicate that an OAM-multiplexed HSPS with high quality can be constructed by generating higher-dimensional entangled states and sorting them with high efficiency in OAM space. Our method may approach a good HSPS with the deterministic property.

DOI
10.1103/physreva.100.013833

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A heralded single-photon source (HSPS) with competitive single-photon purity and indistinguishability has become an essential resource for photonic quantum information processing. Here we propose a theoretical regime to enhance heralded single-photon generation by multiplexing the degree of freedom of orbital angular momentum (OAM) of down-converted entangled photon pairs emitted from a nonlinear crystal. Experimentally, a proof-of-principle experiment is performed through multiplexing three OAM modes. We achieve a 4747%47 enhancement in the single-photon rate. A second-order autocorrelation function g(2)(0)<0.5{g}^{(2)}(0)<0.5g(2)(0)<0.5 ensures our multiplexed heralded single photons with good single-photon purity. We further indicate that an OAM-multiplexed HSPS with high quality can be constructed by generating higher-dimensional entangled states and sorting them with high efficiency in OAM space. Our method may approach a good HSPS with the deterministic property.
The orbital angular momentum (OAM) carried by photons defines an infinitely dimensional discrete Hilbert space. With OAM modes, high-dimensional quantum states can be achieved for quantum communication and cryptography. Here we demonstrate a heralded single-photon source with a switchable OAM mode, which consists of a heralded single-photon source and an integrated OAM emitter as the mode converter. As the first step, the heralded single-photon source is based on the dispersion-shifted fiber. In this work, the OAM mode (quantized by topological charge l ) carried by the heralded single photon (at fixed wavelength of 1555.75 nm) can be switched within the range of l = 3 – 7 while the mode purity is more than 80%.
We study the correlation properties of single photons carrying orbital angular momentum (OAM) in a Hanbury Brown and Twiss (HBT) type experiment. We have characterized single photon sources obtained by pumping a nonlinear crystal with a laser beam carrying different OAM under same experimental conditions. For twisted heralded single photons carrying OAM, we calculate g(2)(0), a measurable parameter characterizing the quality of a single photon source, and observe an increment with the OAM of the single photon. The single photon behaviour of the heralded photons is observed to be reducing with higher orders of their OAM. An OAM-dependent variation of the photon statistics will be relevant to quantum information experiments involving twisted heralded single photons.
In the realm of quantum information processing, harnessing high-dimensional photonic systems provides a pathway to overcome limitations of traditional two-level systems. Orbital angular momentum (OAM) of light has emerged as a powerful tool for creating and manipulating high-dimensional entanglement, promising increased information capacity and enhanced security in quantum communication protocols. However, conventional methods like spontaneous parametric downconversion encounter challenges due to non-uniform production rates of Laguerre–Gaussian modes. This study explores the potential of spontaneous four-wave mixing in ring-core fibers (RCFs) as a viable platform for generating OAM photon pairs with tailored spectral and spatial properties. We show that by controlling the topological charge of pump photons, correlated, uncorrelated, and anti-correlated photon pairs can be engineered across arbitrary spectral ranges, essential for diverse quantum applications. Experimental noise characterization of the RCF-based source demonstrates a high coincidence-to-accidental ratio exceeding 4000, and a low heralded second-order correlation function ( g H (2) <0.005), which confirms its operation well into the single-photon regime. This work demonstrates the potential of RCFs as a versatile platform for generating structured photon pairs, paving the way for future high-dimensional quantum communication and information processing applications.
The bandwidth of any communication system, classical or quantum, is limited by the number of orthogonal states in which the information can be encoded. Quantum key distribution systems available commercially rely on the two-dimensional polarisation state of photons. Quantum computation has also been largely designed on the basis of qubits. However, a photon is endowed with other degrees of freedom, such as orbital angular momentum (OAM). OAM is an attractive basis to be used for quantum information because it is discrete and theoretically infinite-dimensional. This promises a higher information capacity per photon which can lead to more complex quantum computation protocols and more security and robustness for quantum cryptography. Entanglement of OAM naturally arises from spontaneous parametric down-conversion (SPDC). However, any practical experiment utilising the innately high-dimensional entanglement of the orbital angular momentum (OAM) state space of photons is subject to the modal capacity of the detection system. Only a finite subset of this space is accessible experimentally. Given such a constraint, we show that the number of measured, entangled OAM modes in photon pairs generated by SPDC can be increased by tuning the phase-matching conditions in the SPDC process. We achieve this by tuning the orientation angle of the nonlinear crystal generating the entangled photons.
Engineering single-photon states endowed with orbital angular momentum (OAM) is a powerful tool for quantum information photonic implementations. Indeed, due to its unbounded nature, OAM is suitable for encoding qudits, allowing a single carrier to transport a large amount of information. Most of the experimental platforms employ spontaneous parametric down-conversion processes to generate single photons, even if this approach is intrinsically probabilistic, leading to scalability issues for an increasing number of qudits. Semiconductor quantum dots (QDs) have been used to get over these limitations by producing on-demand pure and indistinguishable single-photon states, although only recently they have been exploited to create OAM modes. Our work employs a bright QD single-photon source to generate a complete set of quantum states for information processing with OAM-endowed photons. We first study hybrid intraparticle entanglement between OAM and polarization degrees of freedom of a single photon whose preparation was certified by means of Hong–Ou–Mandel visibility. Then, we investigate hybrid interparticle OAM-based entanglement by exploiting a probabilistic entangling gate. The performance of our approach is assessed by performing quantum state tomography and violating Bell inequalities. Our results pave the way for the use of deterministic sources for the on-demand generation of photonic high-dimensional quantum states.
Orbital angular momentum (OAM) entanglement states have great potential in enhancing the information capacity in quantum communications. To make full use of the OAM degree of freedom, the measurement and distinction of OAM Bell states become a key step that needs to be accomplished. However, there is still no solution to achieve complete distinction of OAM Bell states at the single-photon level. Here we demonstrate the complete OAM Bell-state measurement without auxiliary photons by using linear optics. Furthermore, we propose a quantum communication network via OAM Bell-state multiplexing, perform a proof-of-principle experiment in the first- and second-order OAM subspaces for two users, and achieve average success probabilities of obtaining information of 91.6% for User-I and 89.1% for User-II. In principle, our scheme allows more users to be added by using high-order OAM Bell states. Our research extends the manipulation method for high-dimensional quantum states and paves the way for the application of OAM multiplexing in quantum communications.