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Asia Communications and Photonics Conference

Bell State Measurement between Two Spectrally Multiplexed Elementary Quantum Links

Ruiming Zhang, Chenzhi Yuan, Yunru Fan, You Wang, Hai‐Zhi Song, Guangwei Deng, Guang‐Can Guo, Qiang Zhou, Hao Li, Lixing You, You Wang, Hai‐Zhi Song, Guang‐Can Guo, Qiang Zhou

Published Nov 5, 2022• 0 citations
Publisher

Abstract

We demonstrate a Bell state measurement (BSM) between two spectrally multiplexed elementary quantum links by using two time-bin photonics qubit generators with different spectral channels. A projection fidelity of >95% is achieved by erasing the spectral distinguishability between adjacent nodes of the two links with single-photon frequency shifting while the separation between spectral channels is carefully designed according to parameters of time-bin qubits.

DOI
10.1109/acp55869.2022.10088554

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We demonstrate a Bell state measurement (BSM) between two spectrally multiplexed elementary quantum links by using two time-bin photonics qubit generators with different spectral channels. A projection fidelity of >95% is achieved by erasing the spectral distinguishability between adjacent nodes of the two links with single-photon frequency shifting while the separation between spectral channels is carefully designed according to parameters of time-bin qubits.
Time-bin entangled states are a promising paradigm for quantum communication between nodes of a quantum network. In addition, high-dimensional time-bin states are easy to generate and could offer significantly improved transmission fidelity compared to standard qubits. However, the overall rate of these transmissions is necessarily diminished because successive higher-dimensional time-bin states must be delayed such that they do not overlap in time. We propose to alleviate this concern by introducing an optical frequency shift on each time bin, taking advantage of quantum wavelength division multiplexing to greatly increase the rate of communication possible within a quantum channel. Here we report frequency shifts over a range of ∼ 2 nm (∼ 240 GHz) of telecom pulses in two time-bins separated by ∼ 250 ps, consistent with the requirements for multiplexing.
We demonstrate a Bell state analyzer that operates directly on frequency mismatch. Based on electro-optic modulators and Fourier-transform pulse shapers, our quantum frequency processor design implements interleaved Hadamard gates in discrete frequency modes. Experimental tests on entangled-photon inputs reveal fidelities of ∼ 98 % for discriminating between the | Ψ + ⟩ and | Ψ − ⟩ frequency-bin Bell states. Our approach resolves the tension between wavelength-multiplexed state transport and high-fidelity Bell state measurements, which typically require spectral indistinguishability.
Large-scale quantum communication systems often require different channels to be connected to multiple networks via frequency conversion, which requires frequency converters to act as relay points for system connectivity. We propose a quantum network for single-photon frequency conversion based on time-bin entanglement, where legitimate users can realize the spanning of communication bands between users by independently choosing the target conversion frequency mode. The results show that the converter in the network can be used as a bridge to completely connect the two networks by cascading the quadratic nonlinear process. Meanwhile, the converted quantum entangled states are demonstrated in entanglement measurements and can be used for entanglement swapping. This scheme is expected to be widely used in scenarios where different networks share quantum resources, switching communication channels and effectively connecting different multiplexed spectrum. This concept also provides significant applications in large-scale metropolitan area networks.
We report on the realization and verification of quantum entanglement between a nitrogen-vacancy electron spin qubit and a telecom-band photonic qubit. First we generate entanglement between the spin qubit and a 637 nm photonic time-bin qubit, followed by photonic quantum frequency conversion that transfers the entanglement to a 1588 nm photon. We characterize the resulting state by correlation measurements in different bases and find a lower bound to the Bell state fidelity of ≥0.77±0.03. This result presents an important step towards extending quantum networks via optical fiber infrastructure.