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Chinese Physics B

Microwave-Field Sensing via Rydberg Entangling-Gate Dynamics

Y. -X. Song, C. Z. Cao, G. -Q. Qin, J. -Z. Han, M. Xue

Published Sep 10, 2026• 0 citations
Publisher

Abstract

Abstract Microwave-induced couplings to nearby Rydberg levels are usually regarded as a source of gate imperfections in neutral-atom quantum processors. Here we show that the same mechanism can instead be exploited as a metrological resource for microwave electrometry. We consider a laser-driven Rydberg controlled- Z gate subjected to an additional microwave coupling during the gate operation. The microwave field modifies the gate dynamics through coherent population leakage into an auxiliary Rydberg state, imprinting its amplitude and detuning onto the final two-qubit state. We characterize this response through the output-state fidelity, quantum Fisher information, and classical Fisher information. The results reveal parameter regimes in which enhanced sensitivity of the gate dynamics to microwave perturbations gives rise to increased estimation precision. Representative Rb and Cs implementations are used to illustrate the generality of the approach and to provide concrete sensitivity estimates. More broadly, our results demonstrate that calibrated quantum-gate dynamics can serve as a metrological resource, suggesting a gate-based sensing paradigm at the interface between quantum information processing and quantum sensing.

DOI
10.1088/1674-1056/aea53b

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Abstract Microwave-induced couplings to nearby Rydberg levels are usually regarded as a source of gate imperfections in neutral-atom quantum processors. Here we show that the same mechanism can instead be exploited as a metrological resource for microwave electrometry. We consider a laser-driven Rydberg controlled- Z gate subjected to an additional microwave coupling during the gate operation. The microwave field modifies the gate dynamics through coherent population leakage into an auxiliary Rydberg state, imprinting its amplitude and detuning onto the final two-qubit state. We characterize this response through the output-state fidelity, quantum Fisher information, and classical Fisher information. The results reveal parameter regimes in which enhanced sensitivity of the gate dynamics to microwave perturbations gives rise to increased estimation precision. Representative Rb and Cs implementations are used to illustrate the generality of the approach and to provide concrete sensitivity estimates. More broadly, our results demonstrate that calibrated quantum-gate dynamics can serve as a metrological resource, suggesting a gate-based sensing paradigm at the interface between quantum information processing and quantum sensing.
The Rydberg dipole blockade has emerged as the standard mechanism to induce entanglement between neutral-atom qubits. In these protocols, laser fields that couple qubit states to Rydberg states are modulated to implement entangling gates. Here we present an alternative protocol to implement entangling gates via Rydberg dressing and a microwave-field-driven spin-flip blockade [Y.-Y. Jau et al., Nat. Phys. 12, 71 (2016)]. We consider the specific example of qubits encoded in the clock states of cesium. An auxiliary hyperfine state is optically dressed so that it acquires partial Rydberg character. It thus acts as a proxy Rydberg state, with a nonlinear light shift that plays the role of blockade strength. A microwave-frequency field coupling a qubit state to this dressed auxiliary state can be modulated to implement entangling gates. Logic gate protocols designed for the optical regime can be imported to this microwave regime, for which experimental control methods are more robust. We show that unlike the strong dipole-blockade regime usually employed in Rydberg experiments, going to a moderate-spin-flip-blockade regime results in faster gates and smaller Rydberg decay. We study various regimes of operations that can yield high-fidelity two-qubit entangling gates and characterize their analytical behavior. In addition to the inherent robustness of microwave control, we can design these gates to be more robust to laser amplitude and frequency noises at the cost of a small increase in Rydberg decay.
The advent of digital neutral-atom quantum computers relies on the development of fast and robust protocols for high-fidelity quantum operations. In this work, we introduce a novel scheme for entangling gates using four atomic levels per atom: a ground-state qubit and two Rydberg states. A laser field couples the qubit to one of the two Rydberg states, while a microwave field drives transitions between the two Rydberg states, enabling a resonant dipole-dipole interaction between different atoms. We show that controlled- Z gates can be realized in this scheme without requiring optical phase modulation and relying solely on a microwave field with time-dependent phase and amplitude. We demonstrate that such gates are faster and less sensitive to Rydberg decay than state-of-the-art Rydberg gates based on van der Waals interactions. Moreover, we systematically stabilize our protocol against interatomic distance fluctuations and analyze its performance in realistic setups with rubidium or cesium atoms. Our results open up new avenues to the use of microwave-driven dipolar interactions for quantum computation with neutral atoms.
We demonstrate the use of an auxiliary microwave field to extend the bandwidth sensitivity of Rydberg-atom-based microwave electrometry. Electromagnetically induced transparency (EIT) and Autler-Townes (AT) splitting in Rydberg atom microwave electrometry provide advantageous sensitivity for the resonant detection of microwave (MW) fields because the Stark shift of the target Rydberg state takes the linear form of AT splitting. However, the sensitivity is reduced by several orders of magnitude for detuned MW fields because the Stark shift of the target Rydberg state depends on a weak nonlinear effect. We show that the auxiliary microwave field with appropriate Rabi frequency or detuning could shift the atomic energy levels to bring a particular Rydberg-Rydberg transition of interest for microwave sensing into resonance with the target microwave field. Using the atomic superheterodyne method, we verified the general method that regulates Rydberg energy levels using an auxiliary microwave field. The experimental results of this study confirm that this technique works efficiently for detecting microwave fields detuned by up to 100 MHz from resonance with the field-free Rydberg-Rydberg transition used for sensing. The measurement sensitivity of the detuned target field is increased by a factor of 10 compared with that achieved without the application of the auxiliary dressing field.
The Rydberg atom-based microwave electric field sensor has high sensitivity for weak RF-field detection. Selection of Rydberg states with larger electric dipole moment is beneficial to enhance the sensitivity, and we choose Rydberg states with its principal quantum number up to n ∼ 80. We study the probe laser transmission response to a microwave field for these chosen high Rydberg states at room temperature. It agrees well with theoretical simulation based on an optical Bloch equation with considered microwave-atom interaction and Doppler broadening effect. In our experiment, the microwave sensing sensitivity based on 85 Rb transition | 78 S 1 / 2 ⟩ → | 78 P 3 / 2 ⟩ arrives at 5.102(49) nV cm − 1 Hz − 1 / 2 at 1 kHz.
Interacting many-body systems display enhanced sensitivity close to critical transition points due to diverging quantum fluctuations. This criticality-based enhancement has been suggested as a potential resource for applications in precision metrology. Here we demonstrate many-body critical enhanced metrology for the sensing of external microwave electric fields in a non-equilibrium Rydberg atomic gas. We show that small variations in external driving lead to a large variation in the population of Rydberg states around criticality and to a notable change in the optical transmission signal. For continuous optical transmission at the critical point, we quantify the enhanced sensitivity extracting the Fisher information, which shows a three orders of magnitude increase due to many-body effects compared with single-particle systems. These results demonstrate that critical properties of many-body systems are promising resources for sensing and metrology applications. Interacting quantum systems near criticality have been proposed as potential probes for quantum metrology. An experiment with Rydberg atoms now proves the enhanced sensitivity of critical many-body systems to small variations in external parameters.
Abstract Quantum sensing and metrology present one of the most promising near-term applications in the field of quantum technologies, with quantum sensors enabling unprecedented precision in measurements of electric, magnetic, or gravitational fields and displacements. Experimental loss at the detection stage remains one of the key obstacles to achieving a truly quantum advantage in many practical scenarios. Here, we combine the capabilities of Rydberg atoms to both sense external fields and be used for quantum information processing, thereby largely overcoming the issue of detection losses. While utilising the large dipole moments of Rydberg atoms in an ensemble to achieve single-shot precision of (217 ± 8) μ V cm −1 for a very short 160-ns-long microwave pulse, we employ inter-atomic dipolar interactions to take advantage of an error-prevention protocol that protects information against conventional losses at the detection stage. Counterintuitively, the protocol’s idea is based on introducing an additional non-linear, lossy quantum channel, which results in a threefold enhancement of Fisher information. The presented results pave the way for broader adoption of quantum-information-inspired enhancements enabled by intrinsic interactions present in a sensor system, and more broadly in practical quantum metrology and communication, without the need for a general-purpose quantum computer.