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arXiv:2212.00185

Phase-Resolved Rydberg Atom Field Sensing using Quantum Interferometry

Samuel Berweger, Alexandra B. Artusio‐Glimpse, Andrew P. Rotunno, Nikunjkumar Prajapati, Joseph D. Christesen, Kaitlin Moore, Matthew T. Simons, Christopher L. Holloway

Published Dec 1, 2022• 0 citations
arXivHTMLPDF

Abstract

Although Rydberg atom-based electric field sensing provides key advantages over traditional antenna-based detection, it remains limited by the need for a local oscillator (LO) for low-field and phase resolved detection. In this work, we demonstrate that closed-loop quantum interferometric schemes can be used to generate a system-internal reference that can directly replace an external LO for Rydberg field sensing. We reveal that this quantum-interferometrically defined internal reference phase and frequency can be used analogously to a traditional LO for atom-based down-mixing to an intermediate frequency for lock-in phase detection. We demonstrate that this LO-equivalent functionality provides analogous benefits to an LO, including full 360$^\circ$ phase resolution as well as improved sensitivity. The general applicability of this approach is confirmed by demodulating a four phase-state signal broadcast on the atoms. Our approach opens up new sensing schemes and provides a clear path towards all-optical Rydberg atom sensing implementations.

DOI
10.48550/arxiv.2212.00185

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Although Rydberg atom-based electric field sensing provides key advantages over traditional antenna-based detection, it remains limited by the need for a local oscillator (LO) for low-field and phase resolved detection. In this work, we demonstrate that closed-loop quantum interferometric schemes can be used to generate a system-internal reference that can directly replace an external LO for Rydberg field sensing. We reveal that this quantum-interferometrically defined internal reference phase and frequency can be used analogously to a traditional LO for atom-based down-mixing to an intermediate frequency for lock-in phase detection. We demonstrate that this LO-equivalent functionality provides analogous benefits to an LO, including full 360∘^\circ∘ phase resolution as well as improved sensitivity. The general applicability of this approach is confirmed by demodulating a four phase-state signal broadcast on the atoms. Our approach opens up new sensing schemes and provides a clear path towards all-optical Rydberg atom sensing implementations.
Although Rydberg-atom-based electric field sensing provides key advantages over traditional antenna-based detection, it remains limited by the need for a local oscillator (LO) for low-field and phase-resolved detection. In this work, we demonstrate that closed-loop quantum interferometric schemes can be used to generate a system-internal reference that can directly replace an external LO for Rydberg field sensing. We reveal that this quantum interferometrically defined internal reference phase and frequency can be used analogously to a traditional LO for atom-based down-mixing to an intermediate frequency for lock-in phase detection. We demonstrate that this LO-equivalent functionality provides analogous benefits to an LO, including full ${360}^{\ensuremath{\circ}}$ phase resolution as well as improved sensitivity. The general applicability of this approach is confirmed by demodulating a four-phase-state signal broadcast on the atoms. Our approach may open up new sensing schemes and although the present implementation still uses an auxiliary rf field, we provide a clear path toward all-optical Rydberg-atom sensing implementations by discussing several schemes that allow for all-optical rf phase detection without the need for an external rf LO field.
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Rydberg atom radio-frequency sensors are a unique platform for precision electromagnetic field measurement; e.g., they have extraordinary carrier bandwidth spanning MHz to THz and can be self-calibrated. These photonic sensors use lasers to prepare and read out the atomic response to a radio-frequency electromagnetic field. Most work on Rydberg atom sensors centers on radio-frequency electric field strength because the sensor functions as a square law detector, unless an external radio-frequency heterodyning field is used. A heterodyning field acts as a local oscillator and enables phase readout at the expense of the radio-frequency equipment necessary to generate it. In order to overcome the disadvantages of a radio-frequency local oscillator, we investigate all-optical phase-sensitive detection using a five-level closed-loop excitation scheme. We show that under finite detuning of the loop fields, the atomic response oscillates at the frequency of the detuning. The oscillation is transferred to a probe laser absorption signal. The phase, frequency, and amplitude of the radio-frequency signal are imprinted on the oscillatory dynamics and can be determined using demodulation and matched filter techniques applied to the probe laser transmission signal.
We propose and investigate a Rydberg atom sensor based on a loop-level structure, which utilizes the eigenfrequencies of the energy levels as a reference. This design eliminates the need for the local oscillator (LO) electric field required in the traditional superheterodyne structure while maintaining a linear relationship between the readout signal and the microwave (MW) electric field to be measured, along with exhibiting significantly lower harmonic distortion. For experimental validation, we implemented a cesium atomic system based on the loop five-level structure. The system achieved a sensitivity of 62 nVcm -1 Hz -1/2 and maintained 30 dB of harmonic suppression even near the nonlinear operational region under the strong electric field, which is approximately 20 dB higher than that of the superheterodyne structure. This work demonstrates that loop-level-based atomic sensors enable high-sensitivity and wide-dynamic-range (including nonlinear region) MW detection, making them particularly suitable for receiving frequency- and phase-modulated signals that are insensitive to power variations.
Rydberg atoms have emerged as a versatile and efficient platform for high-sensitivity quantum sensing of free-space electric fields, with remarkable progress in detecting low-frequency signals. To date, low-frequency Rydberg receivers have relied on a constant bias field, typically realized via intra-cell electrodes or Rydberg plasmas generated by photoelectric effects or inter-atomic interactions. While these approaches improve sensitivity, they suffer from inherent challenges in calibration, long-term stability, and robustness, hindering practical deployment. Here, we propose, design, and experimentally demonstrate a quantum sensing scheme for low-frequency electric signals using modulated auxiliary fields in Rydberg atoms. Unlike conventional methods that employ external DC electric fields that are often fully shielded by adsorbed atom layers on the cell walls, we introduce an AC-field modulation strategy. The incoming low-frequency signal mixes with the auxiliary field, and together they induce Stark shifts of the Rydberg level. These shifts are mapped onto the probe laser via electromagnetically induced transparency (EIT), in a manner analogous to heterodyne detection. We demonstrate a sensitivity of 7.5±2.6 μV/(cm⋅Hz1/2)7.5 \pm 2.6~\mathrm{μV/(cm\cdot Hz^{1/2})}7.5±2.6 μV/(cm⋅Hz1/2) at 5 kHz and a minimal detectable field of 0.26±0.04 μV/cm0.26 \pm 0.04~\mathrm{μV/cm}0.26±0.04 μV/cm with an integration time of 1000 s. Furthermore, we extend this approach to systematically analyze the performance of generalized auxiliary fields containing multiple frequency components. By virtue of modulated auxiliary field and quantum frequency mixing, our results establish a robust and systematic framework for quantum sensing of low-frequency electric fields with Rydberg atoms, offering improved sensitivity, stability, and immunity to environmental drifts.
We design phase-sensitive Rydberg-atom interferometry by implementing Floquet electromagnetically induced transparency (FEIT). The FEIT mixes the sidebands of a Rydberg state induced by a megahertz radio frequency (rf) field and recombines them into FEIT bands. The FEIT bands act as screens to present the interference between paths with different phases, which are transitions between the sidebands and excited states. This interferometry can measure the phase of a megahertz rf field without a local rf reference field. A phase reference is supplied to the atoms via a periodic electrical signal in the FEIT. We demonstrate that the megahertz rf phase can be resolved over the full $2\ensuremath{\pi}$ range with a theoretical accuracy of ${10}^{\ensuremath{-}4}$ rad. Moreover, the rf amplitude can also be resolved with higher accuracy than with the traditional EIT-based scheme.