Nankai University proposes efficient characterization method for high-dimensional optical quantum entanglement
High-dimensional entanglement not only enables more bits to be encoded than in the two-dimensional case to increase the communication capacity over quantum channels, but also improves robustness to noise.
As a new endowment degree of freedom of photons, orbital angular momentum (OAM) has theoretically infinite dimensions, providing an effective way to solve the capacity bottleneck problem of optical communication systems. 2001, Physics Nobel Laureate Professor Anton Selinger and others first proposed the use of photonic OAM to achieve high-dimensional quantum entanglement, which not only can substantially increase the information carrying capacity of photons, but also can improve the quantum It has received a lot of attention because it can not only increase the information carrying capacity of photons significantly, but also improve the security of key transmission. However, one of the challenges in the practical application of photonic OAM is to develop efficient methods for characterizing the entangled states of high-dimensional OAM. The conventional full quantum state lamination is the standard technique to obtain all the information of quantum states, but it becomes impractical in high-dimensional systems because the number of required measurements grows exponentially with dimensionality. Therefore, it is highly expected that effective methods can be found to characterize high-dimensional entangled states with as few measurements as possible without introducing unnecessary assumptions.
Recently, the research group of Prof. Yongnan Li at the School of Physical Sciences of Nankai University and Prof. Huitian Wang at Nanjing University have proposed a fast non-scanning quantum state lamination method using two-dimensional detectors for the characterization of high-dimensional orbital angular momentum of photons. The research results were published in Physical Review Letters as "Two-Measurement Tomography of High-Dimensional Orbital Angular Momentum Entanglement". The core idea is to replace the conventional single-pixel detector with a two-dimensional array detector, and to demodulate high-dimensional quantum information from two-dimensional quantum conformal counting based on the interference principle and the Fourier transform.
The method is characterized as non-scanning and dimension-independent, and high-fidelity density matrix reconstruction can be achieved with only two measurements for arbitrary dimensional two-photon OAM entangled states. The idea can also be extended to other spatial mode entanglement, multi-photon entanglement and mixed state entanglement, laying the foundation for the realization of high-capacity quantum communication and quantum process layer analysis. The future combination with machine learning will provide more interesting and efficient measurement ideas for complex cases, such as high-dimensional optical quantum information applications in the atmosphere and optical fibers.
