[Enlarge image]Artist’s representation of propagation of pulses and entangled photons in a fiber-loop system for a few round trips. The synthetic temporal space is created by the delay between the temporal modes as the number of round trips increases (depicted here as different five-level spirals). [Adapted from M. Monika et al., Nat. Photonics, doi: 10.1038/s41566-024-01546-4 (2024).]
Quantum walks1 are a physics-rich framework for quantum information processing such as universal quantum computing. In this scenario, synthetic photonic lattices2 are promising platforms to implement quantum walks on large topologies at reduced device complexity. In a synthetic photonic lattice, the real space dimension—the optical path of the walker—is replaced by an artificial one, which is encoded into the photon’s degree of freedom. Discrete time modes,3 or time bins, offer an ideal platform to create scalable synthetic temporal photonic lattices4 (TPLs) in standard telecom networks. Yet, despite the intriguing potential of TPLs, their use in quantum information processing is still elusive.
In recent work5, we used TPLs for scalable quantum information processing based on discrete-time quantum walks of d-level time-bin entangled photons. To this end, we utilized a fully fiber-integrated coupled-loop system, consisting of two loops of different lengths that are interconnected through a variable coupler, with a series of two periodically poled lithium niobate waveguides as an entanglement source.
Our system is distinctive in two main respects. First, the variable coupler, which can be dynamically switched at different coupling ratios, enables control over the quantum walk’s evolution. Second, the system offers the tremendous benefit of simultaneously supporting classical light and entangled photons while allowing independent control of both.
Specifically, light can enter the system at defined modes (lattice grid points) in one loop through an optical gate and then dynamically couple to the other loop through the variable coupler. As pulses propagate through the loops, they arrive at the coupler at different times, given by the difference in fiber lengths. Depending on the targeted operation, the pulses remain in the loops for a desired number of round trips (two and four in the example shown). The pulses are then taken out of the long loop and injected into the entanglement source to generate two- and four-level time-bin-entangled photons. These are sent back into the coupled fiber-loop system for quantum state processing.
The ability to control the dynamics of the quantum walk enables measurement of two-level quantum interference without post-selection, and enhances detection efficiencies and coincidence counts for both two- and four-level entangled states by optimizing the quantum walk evolution. Our work unveils the potential of TPLs for scalable quantum information processing, including boson sampling and quantum metrology, over telecom-ready architectures.
Researchers
Stefania Sciara, Agnes George and Roberto Morandotti, INRS-EMT, Canada
Monika Monika, INRS-EMT and Abbe Center of Photonics, Germany
Farzam Nosrati, INRS-EMT and Univ. degli Studi di Palermo, Italy
Rosario Lo Franco, Univ. degli Studi di Palermo, Italy
Riza Fazili, Univ. of Ottawa, Canada
Andre Luiz Muniz and Ulf Peschel, Friedrich-Schiller Univ., Germany
Arstan Bisianov, Technische Univ. Braunschweig, Germany
William Munro, Okinawa Institute of Science and Technology, Japan
Mario Chemnitz, Leibniz Institut für Photonische Technologien, Germany
References
1. S.E. Venegas-Andraca. Quantum Inf. Process. 11, 1015 (2012).
2. L. Yuan et al. Optica 5, 1396 (2018).
3. C. Reimer et al. Science 351, 1176 (2016).
4. A. Regensburger et al. Nature 488, 167 (2012).
5. M. Monika et al. Nat. Photonics, doi: 10.1038/s41566-024-01546-4 (2024).