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arXiv:2505.15473 · Physical Review A

Fast and robust detection of single Rydberg excitations in mesoscopic ensembles

Sven Schmidt, Aaron Thielmann, Thomas Niederprüm, Herwig Ott

Published Aug 19, 2025• 0 citations
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Abstract

We propose a novel nondestructive method for the detection of single Rydberg excitations in a mesoscopic ensemble. The protocol achieves high fidelities on a microsecond timescale and is robust against changes in the probe laser frequency. The technique relies on optical pumping in Autler Townes configuration, whose efficiency is controlled by the presence or absence of a Rydberg excitation. Taking rubidium atoms as an example, we give realistic estimates for the achievable fidelities and parameters. However, our protocol can be transferred to any other atomic species that features multiple stable states. Our protocol is applicable in quantum simulation and quantum information processing with mesoscopic ensembles requiring fast and high-fidelity Rydberg state detection.

DOI
10.1103/964l-npcf

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We propose a novel nondestructive method for the detection of single Rydberg excitations in a mesoscopic ensemble. The protocol achieves high fidelities on a microsecond timescale and is robust against changes in the probe laser frequency. The technique relies on optical pumping in Autler Townes configuration, whose efficiency is controlled by the presence or absence of a Rydberg excitation. Taking rubidium atoms as an example, we give realistic estimates for the achievable fidelities and parameters. However, our protocol can be transferred to any other atomic species that features multiple stable states. Our protocol is applicable in quantum simulation and quantum information processing with mesoscopic ensembles requiring fast and high-fidelity Rydberg state detection.
In an atomic ensemble, quantum information is typically carried as single collective excitations. It is very advantageous if the creation of single excitations is efficient and robust. A Rydberg blockade enables deterministic creation of single excitations via a collective Rabi oscillation by precisely controlling the pulse area, being sensitive to many experimental parameters. In this paper, we implement the adiabatic rapid passage technique to the Rydberg excitation process in a mesoscopic atomic ensemble. We make use of a two-photon excitation scheme with an intermediate state off-resonant and sweep the laser frequency of one excitation laser. We find the chirped scheme preserves internal phases of the collective Rydberg excitation and is more robust against variance of laser intensity and frequency detuning.
The amplification of quantum information carried by a single quantum excitation is a recurring challenge across diverse quantum platforms. The coupling between a single qubit and a mesoscopic ensemble of spins, for example, can be leveraged to realize non-destructive detection of the qubit state. However, realizing robust couplings between such systems is experimentally challenging and typically requires programmable quantum gates or native long-range interactions. Here, we introduce a platform that couples a single qubit, encoded in the ground-to-Rydberg transition of a control atom, to a Rydberg-dressed target ensemble of ground-state atoms trapped in an optical lattice. We show that the state of the control qubit can be coherently mapped onto the ensemble via a qubit-controlled collective phase shift. By Rydberg-dressing the ensemble, the controlled phase shift per target atom becomes independent of the number of target atoms, making the protocol intrinsically insensitive to atom-number fluctuations and atom loss, which are the dominant experimental imperfections in our system. Exploiting the collective response of up to eight target spins, we demonstrate the efficacy of the scheme by realizing non-destructive detection of a single Rydberg excitation with a state-assignment fidelity of F=99.81−1.47+0.17 %\mathcal{F} = 99.81^{+0.17}_{-1.47}\,\%F=99.81−1.47+0.17​%. Our approach demonstrates the key ingredients for high-fidelity transfer of quantum information from a single qubit to a mesoscopic ensemble, opening a route to non-destructive mid-circuit readout of Rydberg states and to efficient interfaces between single qubits and photonic modes.
We demonstrate a new approach for fast preparation, manipulation, and collective readout of an atomic Rydberg-state qubit. By making use of Rydberg blockade inside a small atomic ensemble, we prepare a single qubit within $3\text{ }\text{ }\ensuremath{\mu}\mathrm{s}$ with a success probability of ${F}_{p}=0.93\ifmmode\pm\else\textpm\fi{}0.02$, rotate it, and read out its state in $6\text{ }\text{ }\ensuremath{\mu}\mathrm{s}$ with a single-shot fidelity of ${F}_{d}=0.92\ifmmode\pm\else\textpm\fi{}0.04$. The ensemble-assisted detection is 103{10}^{3}103 times faster than imaging of a single atom with the same optical resolution, and enables fast repeated nondestructive measurement. We observe qubit coherence times of $15\text{ }\text{ }\ensuremath{\mu}\mathrm{s}$, much longer than the $\ensuremath{\pi}$ rotation time of 90 ns. Potential applications ranging from faster quantum information processing in atom arrays to efficient implementation of quantum error correction are discussed.
The dipole blockade of multiple Rydberg excitations in mesoscopic atomic ensembles allows the implementation of various quantum information tasks using collective states of cold, trapped atoms. Precise coherent manipulations of the collective ground and single Rydberg excitation states of an atomic ensemble requires the knowledge of the number of atoms with small uncertainty. We present an efficient method to acquire such information by interrogating the atomic ensemble with resonant pulses while monitoring the resulting Rydberg excitations. We show that after several such steps accompanied by feedback the number of atoms in an ensemble can be assessed with high accuracy. This will facilitate the realization of high-fidelity quantum gates, long-term storage of quantum information, and deterministic sources of single photons with Rydberg-blockaded atomic ensembles.
We demonstrate theoretically a parallelized C-NOT gate which allows us to entangle a mesoscopic ensemble of atoms with a single control atom in a single step, with high fidelity and on a microsecond time scale. Our scheme relies on the strong and long-ranged interaction between Rydberg atoms triggering electromagnetically induced transparency. By this we can robustly implement a conditional transfer of all ensemble atoms between two logical states, depending on the state of the control atom. We outline a many-body interferometer which allows a comparison of two many-body quantum states by performing a measurement of the control atom.
We present an all-optical protocol for detecting population in a selected Rydberg state of alkali-metal atoms. The detection scheme is based on the interaction of an ensemble of ultracold atoms with two laser pulses: one weak probe pulse which is resonant with the transition between the ground state and the first excited state, and a pulse with high intensity which couples the first excited state to the selected Rydberg state. We show that by monitoring the absorption signal of the probe laser over time, one can deduce the initial population of the Rydberg state. Furthermore, it is shown that---for suitable experimental conditions---the dynamical absorption curve contains information on the initial coherence between the ground state and the selected Rydberg state. We present the results of a proof-of-principle measurement performed on a cold gas of 87Rb^{87}\mathrm{Rb}87Rb atoms. The method is expected to find application in quantum computing protocols based on Rydberg atoms.