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arXiv:2302.03045 · Physical Review A

Measuring ultrafast time-bin qudits

Frédéric Bouchard, Kent Bonsma-Fisher, Khabat Heshami, Philip J. Bustard, Duncan G. England, Benjamin Sussman

Published Feb 22, 2023• 21 citations
arXivHTMLPDF

Abstract

Time-bin qudits, which are valued in quantum communication protocols for their efficiency and robustness, are made by encoding information into the relative arrival times of photons. However, their practicality has been limited due to the difficulty of the measurements needed to extract this information. Here, the authors demonstrate an effective experimental technique that uses active and passive optical elements to conduct single-shot measurements of ultrafast four-time-bin qudits.

DOI
10.1103/physreva.107.022618

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Time-bin qudits, which are valued in quantum communication protocols for their efficiency and robustness, are made by encoding information into the relative arrival times of photons. However, their practicality has been limited due to the difficulty of the measurements needed to extract this information. Here, the authors demonstrate an effective experimental technique that uses active and passive optical elements to conduct single-shot measurements of ultrafast four-time-bin qudits.
The temporal degree of freedom of single photons is a promising avenue for many quantum information tasks. Here, we experimentally investigate the feasibility of time-bin states of light at the picosecond timescale, known as ultrafast time-bin encoding, for applications in quantum communications, quantum simulations, and quantum information processing. With the ability to generate, manipulate, and measure ultrafast time-bin states of light at the single photon level, we enable the use of temporal states of light in a wide range of quantum applications.
The photonic temporal degree of freedom is one of the most promising platforms for quantum communication over fiber networks and free-space channels.In particular, time-bin states of photons are robust to environmental disturbances, support high-rate communication, and can be used in high-dimensional schemes.However, the detection of photonic time-bin states remains a challenging task, particularly for the case of photons that are in a superposition of different time bins.Here, we experimentally demonstrate the feasibility of picosecond time-bin states of light, known as ultrafast time bins, for applications in quantum communications.With the ability to measure time-bin superpositions with excellent phase stability, we enable the use of temporal states in efficient quantum key distribution protocols such as the BB84 protocol.
The encoding of quantum information in photonic time-bin qubits is apt for long-distance quantum communication schemes. In practice, due to technical constraints such as detector response time, or the speed with which copolarized time-bins can be switched, other encodings, e.g., polarization, are often preferred for operations like state detection. Here, we present the conversion of qubits between polarization and time-bin encodings by using a method that is based on an ultrafast optical Kerr shutter and attain efficiencies of 97% and an average fidelity of $0.827\ifmmode\pm\else\textpm\fi{}0.003$ with shutter speeds near 1 ps. Our demonstration delineates an essential requirement for the development of hybrid and high-rate optical quantum networks.
Quantum states encoded in the time-bin degree of freedom of photons represent a fundamental resource for quantum information protocols. Traditional methods for generating and measuring time-bin-encoded quantum states face severe challenges due to optical instabilities, complex setups, and timing resolution requirements. To circumvent these issues, we leverage an approach based on Hong-Ou-Mandel interference and we propose and demonstrate a robust and scalable protocol to generate and measure arbitrary high-dimensional time-bin quantum states. We experimentally implement the protocol in a photonic setup reaching high-fidelity quantum state tomographies of two- and three-dimensional quantum states encoded in time bins with short temporal separation. We also certify intrasystem polarization-time entanglement of single photons through a nonclassicality test. The demonstrated approach enables access to high-dimensional states and tasks that are practically inaccessible with standard schemes, thereby advancing fundamental quantum information science and opening applications in quantum communication.
One of the most promising ways to transfer quantum information between superconducting qubits is with microwave photons. Enhancing direct quantum channels by time-bin encoding techniques, which map qubit states to single-photon states emitted at different times, allows the detection of photon-loss errors, and thus heralded quantum communication is possible. The authors realize and experimentally benchmark an error-detection scheme that allows them to select only experimental runs in which the photon state was transmitted successfully, yielding significantly improved fidelity of the transfer in this post-selected setting.