Multiplexed Rydberg Sensor Array

• Multiplexed Rydberg sensor arrays are quantum-optical platforms that use spatial, temporal, frequency, and polarization multiplexing to detect electromagnetic fields at microwave and terahertz frequencies.
• They integrate engineered photonic, RF, and atomic subsystems to achieve enhanced bandwidth, sensitivity (with >60 dB isolation), and multi-channel detection across a wide frequency range.
• Key techniques include space-division, frequency-division, spatiotemporal, and dual-ladder multiplexing, enabling advanced applications in spectrum analysis, quantum metrology, and photon counting.

A multiplexed Rydberg sensor array is a quantum-optical platform that leverages spatial, temporal, frequency, and/or internal-state multiplexing of Rydberg atomic sensors to achieve high-throughput, multi-channel detection of electromagnetic fields—principally in the microwave and terahertz domains. Such arrays can dramatically extend the bandwidth, sensitivity, and information capacity of quantum-enabled electrometry and photon detection, transcending the three-fold frequency range bottleneck of conventional receivers by integrating engineered photonic, RF, and atomic subsystems. Implementations range from monolithic vapor cells with multi-tone reception to fully addressable 2D Rydberg-atom arrays, employing design strategies such as space-division, frequency-comb, dual-ladder, and spatiotemporal multiplexing. These architectures enable applications in spectrum analysis, quantum metrology, THz single-photon detection, MIMO communications, and quantum information processing (Zhang et al., 15 Apr 2024, Knarr et al., 2023, Nill et al., 2023, Prajapati et al., 9 Sep 2024, Berweger et al., 26 Feb 2024, Meyer et al., 2022, Kawasaki, 2023, Wu et al., 20 Nov 2025, Fechisin et al., 2022, Glaser et al., 4 Jul 2025).

1. Multiplexing Principles and Techniques

Multiplexing in Rydberg sensor arrays can be implemented through independent or coupled approaches targeting the atomic, optical, and RF hardware layers:

• Space-division multiplexing (SDM): Physically distinct atomic vapor cells, traps, or optical addressing regions ("modules" or "pixels") each function as independent quantum sensors. SDM underpins the dual-band spoof-SPP receiver, where each module integrates its own microwave coupling (horn/slot feed), optical beams, and readout to enable simultaneous multiband detection with negligible crosstalk, limited only by geometric isolation and LO spectral separation (Zhang et al., 15 Apr 2024).
• Frequency-division multiplexing (FDM): Multi-tone RF or optical driving fields selectively couple different Rydberg transitions, each corresponding to a particular channel. Approaches include the use of frequency combs for multi-photon excitation of adjacent Rydberg levels, as in the Comb-EIT array receiver, where each comb tooth addresses a distinct nP level, realizing up to seven channels over 1–40 GHz with minimal crosstalk (Prajapati et al., 9 Sep 2024).
• Spatiotemporal multiplexing (STM): Microsecond- or nanosecond-scale pulsed probe beams are split into multiple spatial channels and temporally interleaved, enabling effective GHz-class RF sampling rates by circumventing the slow EIT relaxation bottleneck of CW operation (Knarr et al., 2023). Each probe pulse interrogates a distinct cell/spot or time slot, and interleaving reconstructs the composite field response.
• Dual-ladder / polarization multiplexing: Orthogonal probe/coupler polarization and frequency shifts select different transition ladders converging on the same or adjacent Rydberg state(s), allowing each ladder to function as an independent sensor for RF polarization components or distinct fields. This reduces cross-talk and supports vector field reconstruction in fiber-coupled arrays and environments where spatial multiplexing is impractical (Berweger et al., 26 Feb 2024).
• Avalanche arrays and photon counting: In optical tweezer arrays, each site or sub-region operates independently as a photon- or THz-sensing pixel. Rydberg facilitation allows a single-photon seed event at one site to cascade through neighbors (avalanche), significantly amplifying the signal and providing spatially resolved single-photon counting (Nill et al., 2023, Fechisin et al., 2022).

2. Atomic-Level and Quantum Optics Architecture

At the core of multiplexed Rydberg sensor arrays are ladder-type EIT schemes in alkali atoms (typically 85Rb, Cs, 39K), often generalized to include multiple addressable ladders or four-level structures. The canonical EIT ladder for microwave detection is

• $|g\rangle=5S_{1/2}$ (Rb), $\Omega_p$ (780 nm probe)
• $|e\rangle=5P_{3/2}$, $\Omega_c$ (480 nm coupling)
• $|r\rangle= nD_{5/2}$ or $nP_{3/2}$ (Rydberg, high $n$)
• Adjacent Rydberg: $|r'\rangle = (n\pm1)P_{3/2}$ or $S_{1/2}$, coupled to $|r\rangle$ by a signal or LO RF field

Probe transmission is modulated by Autler–Townes splitting or AC-Stark shift when the RF field is resonant or far-detuned from the Rydberg transition, respectively. The core susceptibility and response formulas are:

$$\Omega_{\rm RF} = \frac{\mu_{\rm RF} E_{\rm RF}}{\hbar}$$

$$\chi(\omega_p) \propto \frac{N |d_p|^2}{\varepsilon_0\hbar} \frac{1}{\Delta_p + i\gamma_p - \frac{|\Omega_c|^2}{4(\Delta_c + i\gamma_c)} - \frac{|\Omega_{RF}|^2}{4(\Delta_{RF} + i\gamma_{RF})}}$$

Multiplexing is realized by independently addressing optical transitions (frequency, polarization, spatial mode), orthogonally feeding RF signals (spatial separation, frequency spacing), and designing the chip or tweezer geometry to prevent Rydberg blockade or collective effects from coupling distinct channels (Zhang et al., 15 Apr 2024, Prajapati et al., 9 Sep 2024, Berweger et al., 26 Feb 2024).

3. System Hardware and Signal Processing Architectures

A multiplexed Rydberg sensor array integrates the following hardware:

• Atomic sensors: Centimeter-scale vapor cells (for thermal architectures), sub-millimeter microcells, or 1D/2D optical tweezer arrays for single-atom localization. The number of independent sensors is limited by optical routing constraints, cell geometry, and isolation requirements (Zhang et al., 15 Apr 2024, Knarr et al., 2023, Nill et al., 2023).
• Electromagnetic (RF/microwave/THz) feed: Spoof surface-plasmon-polariton chips concentrate RF near the sensor volumes to maximize atom–field coupling. Free-space horns, chip antennas, or focused THz beams distribute signals to each module or pixel (Zhang et al., 15 Apr 2024, Nill et al., 2023).
• Optical addressing: Spatially multiplexed free-space optics, fiber arrays, or dual-polarization beam combiners deliver probe and coupling beams with independent intensity/noise budgets to each pixel (Berweger et al., 26 Feb 2024, Kawasaki, 2023).
• Detection and combiner networks: Photodiode arrays, balanced detectors, or channel electron multipliers (for ionized Rydberg readout) collect the probe response from each sensor. In hybrid MIMO-inspired architectures, probe beams can be optically combined to reduce detector count, balancing complexity and information rate (Wu et al., 20 Nov 2025).
• Signal processing: Heterodyne detection schemes extract beat notes at different frequency offsets for each channel; FFTs or parallel digital lock-in amplifiers demodulate amplitude and phase (Meyer et al., 2022). Algorithmic frameworks (e.g., alternating minimization for optical MIMO combiners) map physical hardware constraints onto optimal precoding/beamforming strategies (Wu et al., 20 Nov 2025).

4. Performance Metrics and Multiplexing Scalability

Performance metrics in multiplexed Rydberg sensor arrays include:

Metric	State-of-the-art values (where specified)	Notes
Sensitivity	$S_E\sim10$–$100\,\mu$V/m/Hz$^{1/2}$	At strong dipole transitions or via chip enhancement (Zhang et al., 15 Apr 2024)
Dynamic range	60–70 dB	Per-band or overall system (Zhang et al., 15 Apr 2024)
Per-channel bandwidth	100 kHz–10 MHz (EIT-limited)	Microsecond-scale EIT time constant; STM: >100 MHz (Knarr et al., 2023)
Frequency range	0.3–24 GHz (6 octaves), up to 116 GHz	Multi-tone, frequency comb, and spatial approaches (Meyer et al., 2022)
Crosstalk/isolation	>60 dB	Ensured via spatial/frequency separation and careful LO selection (Zhang et al., 15 Apr 2024)
Channel count	2 (space-division), 7 (comb), >100 (time/FFT), 10$^4$–10$^5$ (pixelated arrays)	Architecture-dependent; see multiplexing section

Scaling is governed by:

• Laser power and routing overhead: Each sensor requires path-stable, intensity-stabilized optical beams; splitting losses and noise scale with pixel count.
• RF/THz feed isolation: Shared or orthogonally fed LO/Signal beams must prevent leakage or unwanted mixing, often via frequency spacing or polarization.
• Detection bandwidth: EIT relaxation and photodiode speed impose an upper bound on per-channel bandwidth, which sets the maximum number of independent channels resolvable in frequency-division schemes.
• Optical and RF crosstalk: Spatial, spectral, and polarization isolation strategies constrain array layout and operational margins (Zhang et al., 15 Apr 2024, Knarr et al., 2023, Prajapati et al., 9 Sep 2024, Wu et al., 20 Nov 2025).

5. Special Architectures and Application Regimes

Distinct multiplexed Rydberg array architectures enable specific measurement paradigms and applications:

• Software-defined, multi-band heterodyne Rydberg receivers: Multi-tone local oscillator and signal pairs on different Rydberg transitions or within the quadratic Stark regime, enabling simultaneous demodulation of tens to hundreds of tones across 1–116 GHz. FFT-based demodulation enables high-throughput communications protocols and phase-coherent imaging (Meyer et al., 2022).
• Spatiotemporal (STM) architectures: Ultrafast, pulsed, and spatially split probe beams (10–100 ns pulses over multiple channels) allow for RF data rates of 100+ Mbps with low bit-error rates, crucial for GHz-class wideband reception (Knarr et al., 2023).
• Avalanche-type photon/THz detectors: 1D/2D optical tweezer arrays with facilitation-based amplification achieve single-photon sensitivity and high spatial multiplexing with low dark count; the signal from one site is amplified to the entire array on absorption, allowing for high-gain, spatially resolved THz/single-photon detection (Nill et al., 2023, Fechisin et al., 2022).
• Vector electrometry via dual-ladder schemes: Orthogonally polarized and spectrally shifted probe/coupler pairs address the same Rydberg manifold, decomposing RF fields into independent polarization-resolved measurements, suitable for polarization mapping and environments with tight spatial constraints (Berweger et al., 26 Feb 2024).
• Hybrid analog-digital MIMO architectures: Optical/LO and APD reuse, inspired by mmWave beamforming, allow large-N multiplexed Rydberg arrays to approach fully digital performance with drastically reduced hardware footprint; performance scaling is governed by phase quantization in LO chains and optical combiner design (Wu et al., 20 Nov 2025).

6. Practical Limitations, Noise, and Implementation Trade-offs

Key limitations and design considerations include:

• LO power and EIT broadening: Excessive LO field intensities, required in some off-resonant schemes, widen the EIT window and degrade SNR; chip-enhanced fields or local concentration mitigate this (Zhang et al., 15 Apr 2024).
• Inter-channel crosstalk: Spatial separation, frequency offsetting, and optical polarization are primary tools, with required isolation >60 dB to suppress spurious beat notes and intermodulation artifacts (Zhang et al., 15 Apr 2024, Meyer et al., 2022).
• Detection noise and signal floor: Photon shot noise in the probe, electronic noise at photodiodes, and limitations from atomic decoherence rates (e.g., Rydberg-state lifetimes, laser noise).
• Scalability bottlenecks: Optical addressing complexity, RF routing, and integrability of optical components (waveguides, fiber arrays, spatial-light modulators); in multi-pixel readout, per-pixel SNR scales as $\sqrt{P}$ if noise is uncorrelated (Berweger et al., 26 Feb 2024).

7. Outlook and Emerging Directions

Multiplexed Rydberg sensor arrays are positioned to enable:

• Chip-scale, quantum-calibrated, ultra-wideband RF and THz sensing for advanced communication receivers, field imaging, and spectrum monitoring (Zhang et al., 15 Apr 2024).
• Integrated quantum-limited and QND photonic detection protocols for quantum information and metrology (non-demolition photon counting, weak coherent-state discrimination) (Fechisin et al., 2022, Nill et al., 2023).
• High-resolution, minimally-invasive particle and field tracking on sub-micrometer scales, leveraging spatially resolved quantum arrays (Kawasaki, 2023).
• Multifunctional imaging and decoding in MIMO and sparse channel environments with hardware-efficient multiplexed receiver architectures (Wu et al., 20 Nov 2025).
• Further gains through layered multiplexing (combining space, time, frequency, and polarization) and microfabricated multi-band SPP chip structures to flatten the field enhancement over many decades of frequency.

A plausible implication is that continued progress in integration density, micro-optic routing, high-fidelity readout, and digital signal processing will enable the realization of Rydberg sensor arrays with channel numbers, bandwidth, and information rates far in excess of what is achievable through classical electrometry, establishing quantum-enabled platforms for next-generation RF, imaging, and quantum information technologies (Zhang et al., 15 Apr 2024, Knarr et al., 2023, Meyer et al., 2022, Prajapati et al., 9 Sep 2024, Wu et al., 20 Nov 2025).