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arXiv:2412.03060 · Physical Review Research

Single photonic qutrit in a collective Rydberg polariton

Yuechun Jiao, Oliver D. W. Hughes, Max Z. Festenstein, Zhengyang Bai, Jianming Zhao, Weibin Li, Kevin J. Weatherill, Charles S. Adams

Published Aug 29, 2025• 2 citations
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Abstract

Qutrit with highly efficient algorithms and security is imperative in quantum information processing. Here, we demonstrate for the first time the coherent creation, control, and readout of a single photonic qutrit in a cold Rydberg ensemble. In each measurement, an optical photon is stored as a Rydberg polariton through electromagnetically induced transparency. Employing two microwave fields, the polariton is driven into an arbitrary superposition of three collective states, each encoded in a Rydberg state. The collective state is mapped into a photonic time-bin qutrit with the microwave field and read out sequentially. The complete sequence, including preparation, control, and readout, is less than 1.8 µ s , which mitigates decoherence significantly. We measure the coherence of the qutrit with nondestructive Ramsey interferometry, which is preferable for quantum information processing, and find good quantitative agreement with the theoretical model. The ability to write, process, and read out the single photonic qutrit on microsecond timescales with microwave-coupled Rydberg states demonstrates the coherent connectivity among the high Hilbert space of the qutrit. Our study is an important step in exploring qutrit-based quantum information processes and quantum simulation of topological physics with microwave-coupled Rydberg atom ensembles.

DOI
10.1103/3xnw-cpj2

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Qutrit with highly efficient algorithms and security is imperative in quantum information processing. Here, we demonstrate for the first time the coherent creation, control, and readout of a single photonic qutrit in a cold Rydberg ensemble. In each measurement, an optical photon is stored as a Rydberg polariton through electromagnetically induced transparency. Employing two microwave fields, the polariton is driven into an arbitrary superposition of three collective states, each encoded in a Rydberg state. The collective state is mapped into a photonic time-bin qutrit with the microwave field and read out sequentially. The complete sequence, including preparation, control, and readout, is less than 1.8 µ s , which mitigates decoherence significantly. We measure the coherence of the qutrit with nondestructive Ramsey interferometry, which is preferable for quantum information processing, and find good quantitative agreement with the theoretical model. The ability to write, process, and read out the single photonic qutrit on microsecond timescales with microwave-coupled Rydberg states demonstrates the coherent connectivity among the high Hilbert space of the qutrit. Our study is an important step in exploring qutrit-based quantum information processes and quantum simulation of topological physics with microwave-coupled Rydberg atom ensembles.
This thesis presents the preparation, coherent control and interferometric readout of a single qutrit encoded in a cold Rydberg ensemble. A single photon is stored as a collective Rydberg excitation and subsequently manipulated by applying microwave fields coupling different Rydberg levels, before being retrieved after a programmable delay. A time-resolved sequential readout protocol is developed to determine the qutrit state populations. Coherence of the qutrit is investigated using a Ramsey interferometer implemented between Rydberg states, with the resulting fringe pattern demonstrating phase control and multilevel coherence. Following a vacuum failure, the system was fully dismantled, cleaned and reassembled with a new 2D MOT cell. A programme of optimisation and characterisation was carried out using time-of-flight thermometry, spatially resolved absorption imaging and temperature based magnetic field compensation. Sub-Doppler cooling yields a minimum ensemble temperature of T=12.8±0.5 μKT = 12.8 \pm 0.5~\mathrm {\mu K}T=12.8±0.5 μK, and the highest measured optical depth is OD=4.3±0.1\mathrm {OD} = 4.3 \pm 0.1OD=4.3±0.1. This work establishes a robust and flexible platform for investigating high-dimensional quantum information protocols using collective Rydberg states and demonstrates the feasibility of fast, coherent control of single qutrits encoded in an atomic ensemble.
We demonstrate a collectively encoded qubit based on a single Rydberg excitation stored in an ensemble of N entangled atoms. Qubit rotations are performed by applying microwave fields that drive excitations between Rydberg states. Coherent readout is performed by mapping the excitation into a single photon. Ramsey interferometry is used to probe the coherence of the qubit, as well as to test the robustness to external perturbations. We show that qubit coherence is preserved even as we lose atoms from the polariton mode, preserving Ramsey fringe visibility. We show that dephasing due to electric field noise scales as the fourth power of field amplitude. These results show that robust quantum information processing can be achieved via collective encoding using Rydberg polaritons, and hence this system could provide an attractive alternative coding strategy for quantum computation and networking.
We demonstrate a coherent microwave manipulation of a single optical photon based on a single Rydberg excitation in an atomic ensemble. Due to the strong nonlinearities in a Rydberg blockade region, a single photon can be stored in the formation of Rydberg polariton using electromagnetically induced transparency (EIT). The manipulation of the stored single photon is performed by applying a microwave field that resonantly couples the nS 1/2 and nP 3/2 , while the coherent readout is performed by mapping the excitation into a single photon. We achieve a single photon source with g (2) (0) = 0.29 ± 0.08 at 80 S 1/2 without applying microwave fields. By implementing the microwave field during the storage time and retrieval process, we show the Rabi oscillation and modulation of stored photons that can be controlled to retrieve early or late. Rapid modulation frequencies up to 50 MHz can be obtained. Our experimental observations can be well explained via numerical simulations based on an improved superatom model accounting for the dipole-dipole interactions in a Rydberg EIT medium. Our work provides a way to manipulate the stored photons by employing the microwave field, which is significant for developing quantum technologies.
This thesis proposes a means of implementing quantum information processing using photonic qubits as information carriers. Electromagnetically-induced transparency (\textsmaller{EIT}) is used to store information encoded in photons into Rydberg excitations in a cloud of cold atoms, where strong dipole-dipole interactions induce interactions between qubits. After a storage time, information is mapped back into photons collectively emitted from the cloud again via \textsmaller{EIT}. A new experimental apparatus is built to implement non-linear Rydberg quantum optics. A high repetition rate is achieved owing to a \textsmaller{2D-MOT} atom source, and high optical resolution for trapping and probing microscopic atomic ensembles is achieved by the use of aspheric lenses inside the vacuum chamber. A new, high resolution computer control scheme is implemented. This thesis demonstrates that, during the holding time, multiple collective Rydberg excitations at a controlled separation interact with each other to imprint a non-uniform phase gradient resulting in anti-correlation of photon emission. Interactions are observed at up to 151515 times the wavelength of the photonic qubits. These long range interactions offer a promising approach to scaling all-optical quantum computing. Applying resonant microwave fields during the storage time is demonstrated to offer a competitive method of performing sensitive microwave electrometry. A sensitivity of $12 \pm 7 \uV \percm \perRHz$ is found at a frequency of $7.7\GHz$. The high sensitivity is shown to arise from remnant, Rydberg excitations providing an additional source of atom loss from the atomic ensemble, leading to a suppression of photon storage and retrieval efficiency. An additional stage of microwave driving to sanitise the atomic ensemble for recycling is shown to successfully suppress the atom-loss mechanism. The use of successive microwave pulses is shown to provide a feasible approach to interfacing microwave and optical quantum information processing systems. Information encoded as the presence or absence of a microwave field is translated into information encoded as early or late retrieval of single photons, demonstrating proof of principle for an approach to implementing a proposal for an all-optical controlled-zzz gate. Externally driven microwave fields are used to provide rapid, low-loss modulation of the signal retrieved from an atomic ensemble, demonstrating the proof of principle of implementing a probabilistic single photon source that can intensity modulate with low-loss at frequencies of at least $27\MHz$, with evidence that modulation may be achievable at rates in excess of $500\MHz$.
We demonstrate a robust single-photon Ramsey interferometer based on a single Rydberg excitation, where the photon is stored as a Rydberg polariton in an ensemble of atoms. This coherent conversion of the photon to Rydberg polariton enables to split an incoming photon into a superposition state of two Rydberg states by applying microwave fields, which constructs two paths of interferometer. Ramsey interference fringes are demonstrated when we scan either the detuning of the microwave or the free evolution time, from which we can obtain the resonant transition frequency of two Rydberg states. We use the Ramsey-like sequence to demonstrate coherent manipulation of the stored single-photon to construct different interference patterns. In addition, the robustness of the Ramsey interferometer to the fluctuation of incoming photon numbers and optical depth (OD) of the atomic ensemble is tested, showing that the coherent of Ramsey interferometer is preserved for input photon number in a range of R in < 15 and for OD varying from 1.0 to 4.0. The robust interferometer will find its applications in quantum precision measurement.
We use a microwave field to control the quantum state of optical photons stored in a cold atomic cloud. The photons are stored in highly excited collective states (Rydberg polaritons) enabling both fast qubit rotations and control of photon-photon interactions. Through the collective read-out of these pseudospin rotations it is shown that the microwave field modifies the long-range interactions between polaritons. This technique provides a powerful interface between the microwave and optical domains, with applications in quantum simulations of spin liquids, quantum metrology and quantum networks.