Spatiotemporal Multiplexed Rydberg Receiver

Abstract: Rydberg states of alkali atoms, where the outer valence electron is excited to high principal quantum numbers, have large electric dipole moments allowing them to be used as sensitive, wideband, electric field sensors. These sensors use electromagnetically induced transparency (EIT) to measure incident electric fields. The characteristic timescale necessary to establish EIT determines the effective speed at which the atoms respond to time-varying RF radiation. Previous studies have predicted that this EIT relaxation rate causes a performance roll-off in EIT-based sensors beginning at a less than 10 MHz RF data symbol rate. Here, we propose an architecture for increasing the response speed of Rydberg sensors to greater than 100 MHz, through spatio-temporal multiplexing (STM) of the probe laser. We present experimental results validating the architecture's temporal multiplexing component using a pulsed laser. We benchmark a numerical model of the sensor to this experimental data and use the model to predict the STM sensor's performance as an RF communications receiver. For an on-off keyed (OOK) waveform, we use the numerical model to predict bit-error-ratios (BERs) as a function of RF power and data rates demonstrating feasibility of error free communications up to 100 Mbps with an STM Rydberg sensor.

• The paper introduces a spatiotemporal multiplexing architecture that overcomes CW sensor speed limitations by leveraging staggered probe pulses.
• Experimental results show that brief probe pulse durations capture fast EIT transients, enabling error-free RF communication at data rates up to 100 Mbps.
• Numerical simulations confirm improved signal-to-noise ratios across varying RF powers, highlighting the system’s potential for high-speed quantum sensing.

Summary of "Spatiotemporal Multiplexed Rydberg Receiver"

Introduction

The paper "Spatiotemporal Multiplexed Rydberg Receiver" (2302.07316) attempts to overcome limitations in the response speed of Rydberg atom-based electric field sensors used for radio frequency (RF) communication. These sensors exploit the large electric dipole moments in Rydberg states to offer sensitive and wideband electric field detection via electromagnetically induced transparency (EIT). Traditional continuous-wave (CW) Rydberg sensors experience performance roll-off at sub-10 MHz sampling rates, limiting their applicability. The proposed multiplexed architecture leverages spatio-temporal multiplexing to enhance the response speed, achieving data symbol rates of up to 100 MHz.

Spatiotemporal Multiplexing of Rydberg Sensors

The paper introduces an innovative architecture for Rydberg sensors that relies on splitting the probe beam into spatially separated pulse trains and applies temporal delays between them. The beam propagates through different areas of a vapor cell at staggered intervals, leveraging the asymmetric transients in EIT turn-on times to continuously sample the RF field.

Figure 1: Rubidium energy levels used in this work. We define each beam's detuning (dashed lines) from resonance (solid lines) as $\Delta=\omega_{ij}$.

The multiplexing mechanism strategically interleaves probe pulses to exploit fast transients while bypassing hysteretic effects associated with EIT relaxation dynamics. This setup allows the sensor to sample RF fields at rates over 100 MHz, a substantial improvement over CW-based sensors.

Figure 2: Diagram of a 4-beam version of a spatiotemporal Rydberg receiver for increasing the sampling rate of Rydberg atom-based electric field sensors.

Experimental Validation

Experimental results showcase the temporal response of a Rydberg sensor to probe pulses of varying widths, establishing the efficacy of the proposed architecture. The experiments reveal that shorter pulse durations allow sampling via the fast EIT transients before atoms reach steady-state EIT, leading to enhanced response speeds.

Figure 3: Schematic of the experimental layout. CW-p: CW probe laser. CW-c: CW coupling laser. AOM: acousto-optic modulator. EOM: electro-optic modulator. DM: dichroic mirror. PD: photodiode. T: Bias-Tee.

The experimental findings align with numerically simulated atomic time dynamics and highlight the potential for spatial multiplexing to approximate continuous sampling using multiple probe beams.

Performance Predictions

The STM architecture's performance was predicted using experimentally benchmarked numerical models to assess its viability in RF communications. Via simulation, Signal-to-Noise Ratios (SNRs) were calculated across varying RF powers and data rates, revealing error-free communication potential up to 100 Mbps. The analysis confirms improved scaling with data rate and RF power, indicating the feasibility for high-speed quantum sensing applications.

(Figure 4)

Figure 4: Experimentally measured probe laser transmission as a function of center frequency when an 18 GHz RF source is on, and when it is off in Rb 87.

(Figure 5)

Figure 5: Experimental and numerical transmission profiles of probe pulses after passing through Rubidium vapor. For each pulse, we plot the probe transmission with the RF source on and off.

These enhanced metrics demonstrate the STM receiver's promise for more sensitive and rapid RF waveform characterization compared to traditional CW methods.

Conclusion

The proposed spatio-temporal multiplexing architecture signals a significant advancement in the domain of quantum sensing using Rydberg atoms. By optimizing the probe beams' spatial and temporal configurations, the architecture achieves rapid E-field sampling while confronting the limitations evident in CW setups.

(Figure 6)

Figure 6: The SNR per probe pulse of a simulated STM Rydberg sensor as a function of RF power for different data rates.

Practical implications suggest potential for use in RF communications with higher data symbol rates. Future investigations may evaluate integrative techniques such as resonant collisional quenching or vapor cell engineering to optimize further the Rydberg sensors' sampling rates.