High-dimensional maximally entangled orbital angular momentum (OAM) states are a promising resource for enhancing information capacity and robustness in quantum communication. However, it still lacks an effective method to increase the state dimensionality. Here, we theoretically propose an efficient scheme to generate maximally entangled OAM states of ultrahigh dimensionality by manipulating the radial components of a Laguerre-Gaussian (LG) pump beam. By optimizing the complex amplitudes of multiple radial modes of the LG pump light, one can feasibly achieve 101-dimensional OAM-based maximally entangled states. Our scheme has potential applications in high capacity quantum communication networks.
High-dimensional maximally entangled orbital angular momentum (OAM) states are a promising resource for enhancing information capacity and robustness in quantum communication. However, it still lacks an effective method to increase the state dimensionality. Here, we theoretically propose an efficient scheme to generate maximally entangled OAM states of ultrahigh dimensionality by manipulating the radial components of a Laguerre-Gaussian (LG) pump beam. By optimizing the complex amplitudes of multiple radial modes of the LG pump light, one can feasibly achieve 101-dimensional OAM-based maximally entangled states. Our scheme has potential applications in high capacity quantum communication networks.
ObjectiveQuantum communication is an emerging mode of communication with broad application prospects, combining with classical information science and technology. It offers unconditional security and efficient transmission of information, making it a hot research topic in todayƳs communication field. High-dimensional quantum entanglement often exhibits strong nonlocality, enhancing the security in quantum communication processes and playing a crucial role in quantum communication and computing. To meet the demand for high-dimensional entangled states in quantum information science, this paper proposes a method for generating high-dimensional Bell states based on the Orbital Angular Momentum (OAM) of photons, capable of producing the complete set of Bell state basis vectors with high fidelity.MethodsInitially, the Spontaneous Parametric Down-Conversion (SPDC) process involving photon OAM is studied. Furthermore, a Genetic Algorithm (GA) is employed to optimize the quantum state of the pump light, aiming to obtain the required high-dimensional maximally entangled states. We analyze the characteristics of Laguerre-Gaussian (LG) beams in detail and explore their application in the SPDC process. By optimizing the parameters of the pump light, maximally entangled states are generated in three-dimensional, four-dimensional, and five-dimensional spaces.ResultsA comparison of the spatial mode spectral distribution shows that the optimized entangled states possess higher fidelity to the target states. Additionally, by simulating the generation of 16 Bell states, it is verified that the produced quantum states form a complete basis for a four-dimensional Hilbert space.ConclusionThe proposed scheme not only effectively generates high-dimensional entangled states but also enables longer-distance quantum communication and potentially global quantum communication systems. Moreover, it provides new avenues for the application of high-dimensional entangled states in the fields of quantum communication and computing, significantly contributing to the advancement of quantum information science.
Frequency interface, namely, converting the colors of photons while retaining their other features, is indispensable for numerous applications ranging from up-conversion imaging to the multimode quantum network. However, limited by the nonuniform nonlinear frequency-conversion efficiency, constructing the frequency interface for high-dimensional spatial modes is still challenging. Here, to break this fundamental barrier, we construct a high-dimensional (HD) orbital-angular-momentum (OAM) frequency interface via conducting sum-frequency generation between HD OAM states to be converted and a radial structured pump. Specifically, by replacing the conventional Gaussian pump with an optimized coherent superposition of HD Laguerre-Gaussian radial modes (i.e., its azimuthal number is zero), we experimentally achieve the OAM frequency interface in nine dimensions with a record fidelity up to 90.38 %. Additionally, by increasing the number of radial modes, our scheme can be flexibly extended to higher dimension. Such a high-dimensional frequency interface could find potential applications in the high-capacity free-space optical communication and would also pave the way for constructing high-dimensional quantum networks.
Spatially structured quantum states, such as orbital angular momentum (OAM) squeezing and entanglement, is currently a popular topic in quantum optics. The method of generating and manipulating spatial quantum states on demand needs to be explored. In this paper, we generated OAM mode squeezed states of −5.4 dB for the L G 0 + 1 mode and −5.3 dB for the L G 0 − 1 mode directly by an optical parametric oscillator (OPO) for the first time. Additionally, we demonstrated that the OAM mode squeezed and entangled states were respectively generated by manipulating the nonlinear process of the OPO by controlling the relative phase of two beams of different modes, thus making two different spatial multimode pump beams. We characterized the Laguerre-Gaussian (LG) entangled states by indirectly measuring the squeezing for the H G 10 ( 45 ∘ ) mode and H G 10 ( 135 ∘ ) mode, and directly measuring the entanglement between the L G 0 + 1 and L G 0 − 1 modes. The effective manipulation of the OAM quantum state provides a novel insight into the continuous variable quantum state generation and construction on demand for high-dimensional quantum information and quantum metrology.
Twisted photons enable the definition of a Hilbert space beyond two dimensions by orbital angular momentum (OAM) eigenstates. Here we propose a feasible entanglement concentration experiment, to enhance the quality of high-dimensional entanglement shared by twisted photon pairs. Our approach is started from the full characterization of entangled spiral bandwidth, and is then based on the careful selection of the Laguerre–Gaussian (LG) modes with specific radial and azimuthal indices p and l. In particular, we demonstrate the possibility of high-dimensional entanglement concentration residing in the OAM subspace of up to 21 dimensions. By means of LabVIEW simulations with spatial light modulators, we show that the Shannon dimensionality could be employed to quantify the quality of the present concentration. Our scheme holds promise in quantum information applications defined in high-dimensional Hilbert space.
High-dimensional entanglement is a valuable resource for quantum communication, and photon pairs entangled in orbital angular momentum (OAM) are commonly used for encoding high-dimensional quantum states. However, methods for the preparation of maximally entangled states of arbitrary dimensionality are still lacking, and currently used approaches essentially rely on filtering and entanglement concentration. Here, we experimentally realize a method for the generation of high-dimensional maximally entangled OAM states of photon pairs which does not require any of these procedures. Moreover, the prepared state is restricted to the subspace of the specified dimensionality, thus requiring minimal spatial postselection.
Cutting-edge quantum technologies lean on sources of high-dimensional entangled states (HDESs) that reliably prepare high-fidelity target states. The idea to overlap photon paths from distinct but indistinguishable sources was recently introduced for the creation of HDESs, known as entanglement by path identity. In this regard, the use of orbital angular momentum (OAM) modes is promising, as they offer a high-dimensional and discrete Hilbert space to encode information. While entanglement by path identity with OAM has been verified experimentally, a detailed investigation of how the OAM distribution of photon pairs can be engineered to maximize the entanglement is lacking. We address this gap and identify an optimal dimensionality for maximally entangled states (MESs) when the spatial engineering of the pump beam and the path-identity approach are combined. Our theoretical study reveals notable limitations for the fidelity of high-dimensional target states. We also establish the equivalence of entangled biphoton states pumped by a spatially engineered beam and generated via path identity. These findings constitute a valuable step toward the optimized preparation of MESs in high dimensions.