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Optica

Deterministic measurement of a Rydberg superatom qubit via cavity-enhanced single-photon emission

Chao-Wei Yang, Jun Li, Ming-Ti Zhou, Xiao Qiang Jiang, Xiao‐Hui Bao, Jian-Wei Pan

Published Jun 29, 2022• 19 citations
Publisher

Abstract

With Rydberg dipole interactions, a mesoscopic atomic ensemble becomes a superatom that behaves like a single atom but couples collectively with photons. It is potentially a strong candidate as a qubit in quantum information science, especially for quantum networks. In this paper, we report a cavity-enhanced single-photon interface for a Rydberg superatom and demonstrate deterministic qubit readout via a photon burst. We make use of a low-finesse ring cavity to enhance the atom–photon interaction and obtain in-fiber single-photon generation efficiency of 44%. Harnessing the dipole interaction between two Rydberg levels, we may create either a sequence of multiple single photons or nothing, conditioned on an initial qubit state. We achieve a measurement fidelity of 93.0% in 4.8 µs. Our work complements the experimental toolbox of harnessing Rydberg superatoms for quantum information applications.

DOI
10.1364/optica.461287

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With Rydberg dipole interactions, a mesoscopic atomic ensemble becomes a superatom that behaves like a single atom but couples collectively with photons. It is potentially a strong candidate as a qubit in quantum information science, especially for quantum networks. In this paper, we report a cavity-enhanced single-photon interface for a Rydberg superatom and demonstrate deterministic qubit readout via a photon burst. We make use of a low-finesse ring cavity to enhance the atom–photon interaction and obtain in-fiber single-photon generation efficiency of 44%. Harnessing the dipole interaction between two Rydberg levels, we may create either a sequence of multiple single photons or nothing, conditioned on an initial qubit state. We achieve a measurement fidelity of 93.0% in 4.8 µs. Our work complements the experimental toolbox of harnessing Rydberg superatoms for quantum information applications.
With Rydberg dipole interactions, a mesoscopic atomic ensemble may behave like a two-level single atom, resulting in the so-called picture of superatom. It is in potential a strong candidate as a qubit in quantum information science, especially for efficient coupling with single photons via collective enhancement that is essential for building quantum internet to connect remote quantum computers. Previously, preliminary studies have been carried out in demonstrating basic concept of Rydberg superatom, a single-photon source, and entanglement with a single photon, etc. While a crucial element of single-shot qubit measurement is still missing. Here we realize the deterministic measurement of a superatom qubit via photon burst in a single shot. We make use of a low-finesse ring cavity to enhance the atom-photon interaction and obtain an in-fiber retrieval efficiency of 44%. Harnessing dipole interaction between two Rydberg levels, we may either create a sequence of multiple single photons or nothing, conditioned on the initial qubit state. We achieve a single-shot measurement fidelity of 93.2% in 4.8 us. Our work complements the experimental toolbox of harnessing Rydberg superatom for quantum information applications.
We demonstrate a new approach for creating deterministic photon-photon interactions for optical quantum engineering, based on a single-ended medium-finesse optical cavity containing a mesoscopic atomic ensemble. This ensemble is made transparent by a laser beam mapping intracavity photons into Rydberg polaritons. The transparency vanishes when the cloud, acting as a single collective two-level "superatom" with an enhanced coupling to light, is driven from the ground to a Rydberg state. We observe collectively-enhanced Rabi oscillations between these states, optically discriminate them in a single shot with a 95% effciency, and show that a change between the two internal states of the superatom induces a π phase rotation on the light reflected off of the cavity. These ingredients form a complete set of tools for implementing deterministic photonic entangling gates and for generating highly non-classical light without the need for a low-volume high-finesse cavity.
Remote entanglement of matter qubits plays an important role in quantum networks and quantum repeater. Collective excitations generated via Rydberg blockade in an atomic ensemble-known as Rydberg superatoms-are promising candidates due to collectively enhanced atom-photon coupling and Rydberg-enabled nonlinearity. Here, we experimentally realize remote entanglement between two Rydberg superatoms via single-photon interference. The two setups are separated by 3 m and linked with two 20-m fibers, operated with independent control lasers. We verify that the entanglement generated is free from high-order excitation noise that is a key drawback in the traditional Duan-Lukin-Cirac-Zoller scheme. This Letter paves the way for entangling long-distance separated Rydberg superatoms at a high rate, as the success probability of a single-photon-based entangling scheme scales with the square root of the channel transmittance.
Abstract Quantum optics based on highly excited atoms, also known as Rydberg atoms, has cemented itself as a powerful platform for the manipulation of light at the few-photon level. The Rydberg blockade, resulting from the strong interaction between individual Rydberg atoms, can turn a large ensemble of atoms into a system which collectively resembles a single two-level emitter, a so-called Rydberg superatom. The coupling of this artificial emitter to a driving photonic mode is collectively enhanced by Rydberg interactions, enabling strong coherent coupling at the few-photon level in free-space. The exquisite level of control achievable through this has already demonstrated its utility in applications of quantum computing and information processing. Here, we review the derivation of the collective coupling between a Rydberg superatom and a single light mode and discuss the similarity of this free-space setup to waveguide quantum electrodynamics systems of quantum emitters coupled to photonic waveguides. We also briefly review applications of Rydberg superatoms to quantum optics such as single-photon generation and single-photon subtraction.
Heralded storage of photons is crucial for advancing quantum networks. Previous realizations have primarily relied on single atoms strongly coupled to optical cavities. In this work, we present the experimental realization of heralded storage using a Rydberg superatom, a mesoscopic atomic ensemble operating in the strong blockade regime. In our approach, an input photon is initially stored in the superatom via electromagnetically induced transparency. Subsequently, a second photon is emitted conditioned on the success of the first photon's storage. Because of the collectively enhanced interaction, both the storage and the emission of the herald photon can be rather efficient in principle. As a demonstration of this technique, we use it to entangle two remote Rydberg superatoms. This method obviates the need for an intermediate node, which is commonly employed in traditional interference-based remote entanglement schemes. Our results showcase the potential of performing cavity-QED-like experiments with Rydberg superatoms. This work opens pathways for numerous applications in quantum networks and linear optical quantum computing.
We demonstrate a new versatile building block for optical quantum technologies, enabling deterministic quantum engineering of light by combining the advantages of two complementary approaches: cavity quantum electrodynamics and interacting atomic ensembles.Our system is based on an intracavity Rydberg-blockaded atomic ensemble acting as a single two-level superatom.We coherently control its state and optically detect it in a single shot with 95% efficiency.Crucially, we demonstrate a superatom-statedependent π phase rotation on the light reflected from the cavity.Together with the state manipulation and detection, it is a key ingredient for implementing deterministic photonic entangling gates and for generating highly nonclassical light states.