Single-shot measurement of a Rydberg superatom via collective photon burst

Abstract

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 singleshot measurement fidelity of 93.2% in 4.8 µs. Our work complements the experimental toolbox of harnessing Rydberg superatom for quantum information applications.

An Intracavity Rydberg Superatom for Optical Quantum Engineering: Coherent Control, Single-Shot Detection and Optical $π$ Phase Shift

“…In conclusion, the demonstrated coherent state control, the two single-shot state detection methods and the conditional optical π phase shift confirm that combining a Rydberg superatom with a medium-finesse cavity is a viable route towards deterministic optical quantum engineering. The state detection efficiencies match those recently obtained in Rydberg-based experiments operating in free space or in low-finesse resonators [26,27], but the π phase flip is a unique feature, relying on an excellent EIT combined with a strong Rydberg blockade, that would vanish for a low-or high-finesse cavity and would require post-selection for free-space beams [24,32].…”

“…We show that the cloud acts as a single Rydberg superatom with a collectively enhanced coupling to light, which we can coherently manipulate and optically detect in a single shot with a 95% efficiency via the transmission of the cavity. Most importantly, with respect to recent experiments on Rydberg superatoms [25][26][27][28], we successfully unlocked a qualitatively new regime where the phase of the light reflected from the cavity is shifted by π by a single Rydberg excitation, allowing us to detect the latter with a 90% efficiency via a homodyne measurement. This π phase rotation, together with the coherent control and the single-shot state detection, is crucial for implementing two-photon quantum gates [29] and for generating non-classical optical resources for quantum sensing and communications.…”

Sequential generation of multiphoton entanglement with a Rydberg superatom

“…And the experiments with quantum dot [15,16] still have a scaling factor of lower than 0.08. The single-photon efficiency η f is lower than the best value of 44% we observed previously [28]. The reduction is mainly due to a prolonged interval between excitation preparation and retrieval, during which the collective excitation dephases slightly and the photonic retrieval efficiency gets reduced.…”

“…It is practical and efficient to use a low-finesse cavity to boost the collectively enhanced directional emission. As demonstrated in our previous work [28], an overall efficiency (including preparing and fiber coupling) of up to 44% has been achieved. Such an efficient single-photon interface forms the basis of conducting multiphoton experiments.…”

Ultra-low noise quantum memory for quasi-deterministic single photons generated by Rydberg collective atomic excitations

“…Several improvements should be applied to our experiment before it can become a practical alternative. The generation efficiency of the single photon from the Ryd-berg ensemble could be increased by increasing the OD of the ensemble and/or by embedding the ensemble in a low finesse cavity [63]. The quality of the single photon (as measured by the autocorrelation function g (2) (0)) could also be improved by addressing a slightly smaller ensemble and by reaching higher principal quantum number level to increase the Rydberg blockade radius, as was shown in [46], where g (2) (0) values smaller than 10 −3 have been measured.…”