Arbitrary Instantaneous Bandwidth Microwave Receiver via Scalable Rydberg Vapor Cell Array with Stark Comb

TL;DR

This paper addresses the challenge of achieving arbitrary instantaneous bandwidth in Rydberg-atom microwave receivers by introducing a scalable vapor-cell array driven by a Stark comb, which pairs a microwave frequency comb with a position-dependent Stark field to map each LO line to a specific cell. The demonstrated proof-of-principle achieves a 210 MHz instantaneous bandwidth using 21 MFC lines and reports an overall sensitivity of 326.6 nV cm$^{-1}$ Hz$^{-1/2}$, with a two-cell demonstration validating scalability. The method enables parallel, high-bandwidth MW detection and can be extended toward >1 GHz bandwidth using additional LO lines and multi-dressed-state strategies, offering a scalable, low-noise solution for radar, communications, and spectrum monitoring applications.

Abstract

Rydberg atoms have great potential for microwave (MW) measurements due to their high sensitivity, broad carrier bandwidth, and traceability. However, the narrow instantaneous bandwidth of the MW receiver limits its applications. Improving the instantaneous bandwidth of the receiver is an ongoing challenge. Here, we report on the achievement of an arbitrary instantaneous bandwidth MW receiver via a linear array of scalable Rydberg vapor cells with Stark comb, where the Stark comb consists of an MW frequency comb (MFC) and a position-dependent Stark field. In the presence of the Stark field, the resonance MW transition frequency between two Rydberg states is position dependent, so that we can make each MFC line act as a local oscillator (LO) field to resonantly couple one Rydberg cell. Thus, each cell receives part of a broadband MW signal within its instantaneous bandwidth using atomic heterodyne detection, achieving the measurements of the broadband MW signal simultaneously. In our proof-of-principle experiment, we demonstrate the MW receiver with 210~MHz instantaneous bandwidth using an MFC field with 21 lines. Meanwhile, we achieve an overall sensitivity of 326.6~nVcm$^{-1}$Hz$^{-1/2}$. In principle, the method allows for achieving an arbitrary instantaneous bandwidth of the receiver, provided we have enough MFC lines with enough power. Our work paves the way to design and develop a scalable MW receiver for applications in radar, communication, and spectrum monitoring.

Figures (4)

• Figure 1: An arbitrary instantaneous bandwidth MW receiver. (a) Prototype of the receiver. The scalable Rydberg vapor cell array (bottom) is formed of $N$ individual cells along the $x$-axis. The Stark comb consists of an MFC and a position-dependent Stark field $E_{\text{RF}}(\bf r)$. (b) Relevant energy-level diagram for the MW receiver. The Rydberg state $|r_1\rangle$ is detected using EIT, where a probe laser ($\lambda_p$) and a coupling laser ($\lambda_c$) counterpropagate through the cell and drive the ground atoms $|g\rangle$ to the Rydberg state $|r_1\rangle$ via an intermediate state $|e\rangle$. The MFC and broadband frequency signal fields couple the Rydberg transition between $|r_1\rangle$ and $|r_2\rangle$. The resonance MW transition frequency between two Rydberg states is position-dependent, which is controlled by a position-dependent Stark field generated by an RF field.
• Figure 2: (a) Schematic of the experimental setup. An RF electric field is applied to a pair of aluminum electrode plates to generate the position-dependent Stark fields. An MFC as LO fields and a single-tone MW signal are fed to two identical horn antennas, respectively, and simultaneously incident on the Rydberg MW receiver. A cell is placed on the $x$-axis, and a 509 nm Rydberg coupling laser and a 852 nm probe laser counterpropagate through the cell and drive the ground state to the Rydberg state, forming the Rydberg EIT. The transmission of the probe laser is detected by an APD. The electrodes are moved to change the relative position between the cell and the electrodes along the $x$-axis. (b) The black solid line and dots show the calculated and experimental data of the RF electric field strength along the x-axis. The x-coordinate of the black dots presents the chosen 21 positions of cells in the experiment. The closet minimum spacing between two cells is 0.23 cm. The blue solid line presents the calculated resonant MW transition frequency between two Rydberg states along the $x$-axis. Each colored vertical line point demonstrates the range of instantaneous bandwidth at the corresponding x position, which is extracted from (c), and their colors correspond to the colors in (c). The total instantaneous bandwidth is 210 MHz, marked by the dashed lines, i.e., enabling measurement of a 210 MHz broadband MW signal simultaneously. (c) Instantaneous bandwidth of one cell at 21 different positions. The 3 dB bandwidth is labeled by the horizontal dashed grey lines. We measure the signal frequency with a 210 MHz bandwidth from 8.025-8.235 GHz. (d) Power of the beat note as a function of the signal field strength at the indicated signal frequency. The receiver has the same response at the same input power in the linear dynamic range. The flat region indicates that the beat note power reaches the noise level.
• Figure 3: Sensitivity for the cell with MW resonant frequency at 8.13 GHz. The purple region represents the noise level. The red circles show the EIT-AT splitting in a strong field region, and the red solid line shows the calibrated electric field. (b) Sensitivity at different positions. Each colored point corresponds to the color in Fig. \ref{['figure2']}(c).
• Figure 4: Beat note signal for measuring two cells simultaneously. The cells are placed on the most left (red dots) and most right (green dots) ends of the Stark field. The black dots show the noise level. The 3 dB bandwidth is labeled by the horizontal dashed lines.